Multi-Apartment Air Conditioning

INTRODUCTION

  • Author: Jorgen Knox (e: jorgenk@knoxadv.com.au, t: 02 800 33 100, w: KAE)
  • Original Issue Date: 20/02/2015
  • Last Updated: 25/09/2016

This post aims to provide a quick look up reference for AC systems and types. Target audience ; Architects and Developers.

NSW (Australia) has in recent years undergone a boom in residential developments. With rental availability, in most states, now starting to increase this boom will likely slow down. That said, with our country determined to increase population via immigration, an underlying demand will likely always be there.

For each new development the question of air conditioning arises. The answer for some developments is not to provide, others its provide provision to allow tenants to install later.

For the majority of developments, however, air conditioning is seen as a ‘must have’. This being driven more by sales competition, rather than a detailed study on the actual need for air conditioning based on location, solar load, etc.

So we have decided to have air conditioning (AC). The next step is which AC system is to be installed. This decision process is based on many factors including:

  • Will Council allow condensers on balconies
  • Height of the development
  • Is the roof activated for tenants
  • Developer funding
  • Location of development
  • Perceived marketing advantage
  • Perceived (by purchasers and renters) quality of air conditioning system
  • Use of ‘enclosed’ balconies
  • Desire for power and maintenance to be by apartment owner.

The answers to the above will direct the air conditioning system selected.

At the outset, ‘let’s cut to the chase’. A balcony located condenser, and wall hung indoor units provides a low cost effective air conditioning system.  Moving from this system will cost.

The typical next step ‘up’ is sticking with the balcony located condenser, but opting for a ducted, ceiling void located system.

Within reason, if air is delivered into a room in sufficient quantity and at the right temperature, then this provides acceptable AC, from a sales perspective. Obviously a fully designed project will ensure good air flow is achieved (whole room conditioned, no drafts, low noise, low pressure etc). So, from a sales point of view, a wall hung AC unit is the same as a ducted AC system (except for the perceived look and perception).

This post tries to summarise the different AC systems available for multi apartment-residential projects. Much of the data used in this post uses Mitsubishi AC unit data.

Select on Links below, for post data.

Internal Considerations

Energy Code Compliance

Typical Air conditioning Capacities

Air Conditioning Systems – Quick Choice

Air Conditioning Systems – Quick View

AC Summary Table

Indoor AC Unit Types

AC Systems NOT Considered

 

Residential Apartment Design Notes

INTRODUCTION

This post provides typical design advice for apartment AC systems. The author takes no responsibility for use of this post by any persons.

Author: Jorgen Knox (e: jorgenk@knoxadv.com.au, t: 02 800 33 100)
Status: For review and comment, only
Date: 23/09/2016

Load Estimation

The correct load assessment of an apartment is critical to the success of the air conditioning system. The following loads are typically considered for air conditioning apartment design.

Note: The data below is for information only. No warranty, what so ever, is provided or implied.

The following diagram summarises the incident loads onto a typical air conditioning system.

Apartment Loads

Design Conditions

Typical room conditions: 24 Deg C and 55% RH

External: As per C.A.M.E.L

Windows Allow for the shading effect of fixed external building elements, (balconies, etc.).

Discuss in detail with the Client shading effect of blinds/drapes. Provide advice regarding the impact of blinds on the cooling load i.e. an apartment owner may be very disappointed if the curtains need to be closed for the AC unit to achieve design internal temperatures.

On West Facing windows consider performance glazing typically U Value = 3.5, SC = 0.53. Check supply air l/s/m2 and adjust glazing until reasonable air flow achieved.

Walls:     Consider heat gain through outside walls.

[Note: Recalculate U values for walls as building height increases as Outside Surface Air Films Surface Resistivity reduces.]

Ceiling/Roof:        Consider heat gain to ceiling space from fabric and lights.

Thermal Mass: Typically C.A.M.E.L thermal mass used for residential is 350 kg/m3.

Shading: Consider the potential shading effect of adjacent buildings.

Do not normally allow for any shading effect due to planting, (trees), which is often transient.

Infiltration:

Allow for infiltration in cooling loads. In well sealed modern apartment buildings allow the diversified exhaust flow rate as the infiltration load. In C.A.M.E.L this can be entered as a fixed outside air low equal to the diversified exhaust flow rate.

Ceiling Void:

Consider infiltration of out side air to ceiling void if used as a return air plenum. Where practical utilise ducted return air . Ensure that an additional allowance is made in the cooling load to offset infiltration to the ceiling void.

Do not use a roof void as a return air plenum. Roof voids are prone to ingress of out side air. Always ensure that return air is ducted through roof voids and the duct work appropriately insulated. Check application of roof insulation, ie located on underside of roof sheet, or on top of the ceiling.

Make Up Air:

Make up air for exhaust systems is a code requirement. Many buildings are still built with no means of make up air.

No Make up Air – This does not comply with NCC reference standard AS1668.2 (2012).

Make up air (as per infiltration) is a load on the air conditioning system.

Note: Modern building becoming more airtight. Make up air via purpose designed, acoustically treated air intake for controlled infiltration for make-up to kitchen, laundry and toilet exhaust systems is required.

Refer to post Apartment Air Flows

Partition Loads: Consider fabric gain from unoccupied apartment adjacent, above and below.

[Typically allow for half temperature difference between apartments]

Reflectance: Increase overall safety factor by 5% if adjacent areas are highly reflective (ocean, harbour, clad building facades, etc.)

Heat Loads

Under take C.A.M.E.L heat loads for all projects. Consider the following:

Q INTERNAL

Misc. Equipment:

  • TV & Audio Equipment:  

Consider 200W          [Seek client confirmation].

  • Fridge:

Consider 150W          [Seek client confirmation].

  • Cooker: 

Consider 150W [Seek client confirmation].

Misc. Equipment Summary: With diversity consider 545 Watts for internal loads for appliances.

Lights:   

Consider 5 to 9 w/m2. Incorporate upward and downward components and light ballasts and transformers.

Fan: Make allowance for fan gain. Consider Pa with say 120 pa (bulk head unit) or say 250 Pa (ducted unit) in CAMEL settings

People:

Allow for the following people in a zoned apartment:

  •  Master bedroom – 2 people
  • All other bedrooms – 1 person
  • Living areas – Sum of people in master bedroom and other bedrooms plus 1

Allow for the following people in a fully air conditioned apartment:

  •  All bedrooms – 1 person
  • Living area – 2 people

Each person will emit 150W (75 sensible and 75 latent approximately). This is typical for a seated/standing activity.

Q EXHAUSTS

Toilet Exhaust: 

  • Allow Outside air make up to full exhaust quantity for 24 hour toilet exhaust systems.
  • Allow outside air make up to 50% full exhaust quantity if intermittent toilet exhaust quantity.

Minimum air flow rates: 25 l/s

Laundry Exhaust:

  • Allow Outside air make up to full exhaust quantity for 24 hour laundry exhaust systems.
  • Allow outside air make up to 50% full exhaust quantity if intermittent laundry exhaust quantity.

Minimum air flow rates: 40 l/s (dependant on dryer requirements).

Kitchen Exhaust:

  • Allow Outside air make up to full exhaust quantity for 24 hour kitchen exhaust systems.
  • Allow outside air make up to 50% full exhaust quantity if intermittent kitchen exhaust quantity.
  • Air flow rate depends on hood selected (120 l/s is a small hood air flow)

Exhaust Summary: Allowing all systems to run continuously will result in oversized air conditioning, for the majority of operating times. Based on the exhaust flow rates above a diversified flow rate of 60 l/s should be considered.

Kitchen Hood: 120 l/s x 0.5 = 60 l/s

Laundry: 40 l/s x 0.5 = 20 l/s

Bathroom 1: 25 l/s x 0.5 = 12 l/s

Bathroom 2: 25 l/s * 0 = 0 l/s

Diversified Total: circa  60 l/s

Note: On warm or cold days when all systems are operating room conditions will not be maintained.

Safety Factors:

Typical Safety Factors s:

  • Supply Duct Leakage & Heat gain:           5%
  • Return Air Heat Gain:                                     5%
  • Overall Safety Factor:                                    20% (This allows for AC systems to bring an apartments temperature down, if left for an extended period in summer)

Unit Selection

The selected air conditioning unit must be selected under the following minimum conditions:

  • Coil Face Velocity: NO MORE than 2.5m/s based on air conditioning unit ‘fast’ speed at minimum external static, i.e. clean filter condition. Check with unit manufacturer the maximum air flow at which the unit is rated to operate without condensate carryover off the coil.
  • Off coil temperature: The aim here is to have the supply air temperature, thus supply air device temperature above the dew point of the air to avoid condensation. Typically a minimum 0f 11.5 Deg C is used.
  • External Static:     Based on calculated external static. Check static at all speeds to ensure over supply is not occurring (coil velocity < 2.5m/s).
  • Fan Speed:              Typically select units on medium fan speed.
  • Acoustics:                Typically assess on fast speed.

 

Air Conditioning Unit Location

 Ensure that the manufacturer’s recommendations are sought and followed.

The location of the air conditioning unit within the apartment is important. The location must be noise tolerant, provide easy access and enable ductwork etc. to be efficiently circulated.

Often the ceiling below an AC unit is part of a destruction zone (i.e. allows for easy removal of the ceiling should the AC unit need to be fully removed).

 Typically, ceiling mounted units are installed in the entrance lobby, above wet areas or kitchens in each apartment.

 Location over wet areas and kitchens is often done due to tolerance in ceiling heights. Extreme co-ordination with hydraulic services is generally the draw back in this instance.

Where ceiling access is not possible units can be cupboard located.

Condensate Removal

 Ensure that the manufacturer’s recommendations are sought and followed.

Establish the following requirements from the unit manufacturer:

  •  Grade required to ensure that built-in condensate tray operates effectively;
  •  Ensure AC units have integral safety trays (if not provide safety tray to capture leaks/condensate).
  • If condensate removal pump cannot be avoided, ensure that traps, sump, float switch, etc are all correctly installed.

Note: Ceiling mounted units in particular are designed to very close tolerances in order to achieve minimal room ceiling heights. Some draw through units are built with the fan scroll almost sitting in the drain tray. As a consequence there is a tendency for pooled condensate to be lifted sucked out off the tray through the fan and in to the supply air duct work.

 Wherever possible, avoid pumped condensate removal. Ensure that adequate fall is available for a gravity drained condensate system wherever possible.

If pumps are required to be adopted, use pumps factory fitted by the manufacturer. Some pumps operate on extremely fine tolerances and are very difficult to install and commission on site.

Where possible, provide all air conditioning units with drained and insulated safety trays.

Ensure condensate pipe work is correctly installed with no sags. Use copper pipe work where possible at a minimum 22mm Dia.

Ensure condensate pipe work discharges over trapped tundish. Tundish must be visible to occupants.

Architect Note: An indoor AC unit must be positioned to allow for condensate removal. This means considering where the condensate pipework will fall gradually to. Condensate pipework cannot be routed in an up/down fashion. A window or door, in the path between AC unit and tundish,  will prevent condensate removal i.e. pipework cannot pass through these elements in a continuous sloped manner.

[Do not connect directly into sewer pipe work].

Ductwork

 Refer to separate Ductwork post (In Progress) for guidance on appropriate design criteria. Typically, ductwork velocities to not exceed 5m/s.

KAE recommends that solid ductwork be installed except for final connections to grilles etc. Max flex length to be 3m.

All rigid ductwork to be insulated with minimum 25mm thick insulation. Insulation shall generally be applied internally for acoustic purposes.

All flexible ductwork to be supplied with factory installed internal 25mm insulation. All flexible ductwork to be 2 hour fire rated.

 Bulk Heads

 When advising the Architect of clear internal bulk head sizes, allow for ductwork supports, insulation and connection to grilles with OBD’s.

Access

 Adequate access is required for maintenance of the unit and to adjust air flows. Where possible, sufficient access should be provided to allow removal of the unit.

As a minimum access to the following is generally required:

  •  Electrical control panel;
  • Drain connection, trap, site glass;
  • Fan;
  • Compressor, (water cooled packaged unit);
  • Filter Removal;
  • Motorised damper maintenance and motor replacement.

Where possible, provide permanent access to duct dampers to facilitate readjustment of air flows post commissioning. Group dampers to minimise the number of access opening required.

Noise

 Comply with AS2107

 The following minimum acoustic treatments are typical:

  • 50mm internal insulation 3 meters up/down stream of AC unit;
  • Line internally casings housing compressor units;
  • Consider acoustic splitters at each grille or low velocity ductwork at grille;
  • Internally insulate supply and return air header boxes;
  • Provide acoustic elbow on return air grille to ceiling plenum;
  • Provide insulated return air plenum;
  • Advise Architect to specify acoustic door seals for air conditioning cupboards;
  • Allow to internally insulate air conditioning cupboards where directed by Project Acoustic Consultant;
  • Low ductwork and grille velocities

Outside Air Requirements

Outside air supply is required to comply with AS1668.2

Typically 10l/s per person. With filtration this can be reduced to 7.5 l/s per person

 For many apartments outside air is not ducted to the air conditioning units. The NCC/BCA, section F allows us to consider openable doors and windows as a means of providing outside air. Typically a operable opening must be sized at 5% of the room floor area, for compliance with Part F of the NCC (Natural Ventilation).

The NCC provides guidance as to what area of a window is considered as operable. In summary, the whole window, is considered as operable (as apposed to just the physically open part of a window.

window-openning

NCC LINK

[Note/Advise to Client: Opening of doors/windows will result in loss of conditions].

In cases where opening of the doors or windows would mean that internal noise levels are exceeded then an alternative method of introducing outside air will be required:

ALT 1:    Acoustic Air Intake to outside

ALT 2a:    Provide a lobby outside air supply and introduce air via door under or via fire dampered transfer duct.

ALT 2b:    Similar to 2a, above, where the development requires stair pressurisation the associated relief air shaft can be utilised to deliver outside air to each floor. Air to each apartment is then via fire dampered air intake (typically a 300 x 200 intumescent fire damper with acoustic flexible is utilised).

Part Schematic (showing Corridor Outside Air System)

lobby-outside-air

ALT 3:    Provide ducted outside air shaft within apartments (often used in hotel applications)

[Note: Remember to make an appropriate additional allowance on the unit cooling capacity in order to offset this additional load].

Zoning

 Many apartments require the ability to zone the air conditioning, e.g. only condition the bedrooms of an apartment and not the living areas, or vice versa. This type of system is generally termed a ‘day/night change over system’.

Control of the system is achieved by installing day/night motorised zone shut-off dampers which the owner can operate.

Zoning typically allows for the air conditioning unit to be down sized. This is achieved by sizing the unit on the peak load for the day zone only.

[Note: It is essential to point out to the client that loss of conditions will occur on hot days if all zones are operating simultaneously].

Care must be taken to avoid excessive air supply with zoning. If zones are of different sizes and loads, the smaller zone may be over supplied with air. This can be overcome by ‘dumping’ excess air to additional areas outside of the zone.

Ideally a controller is provided in master bedroom and in the day area ( 2 off controllers). Operation of either controller, will ensure that room will control the supply air temperature.

Supply Air Devices

 Refer to Ductwork post (In Progress) of this manual for register and grille selection criteria.

Typically grilles are located within fixed ceilings i.e. no access. Suitable allowance for commissioning is required. This is typically achieved by two methods:

(i)  Install VCD in ductwork with access panel in ceiling.

(ii) Install OBD behind face of grille with adjustment from face of grille

Where OBD’s are installed at face of the register, ensure ductwork velocity is < 4m/s.

Commissioning

 It is often very difficult to arrange access to apartments once they are handed over and occupied. It is generally not possible to gain sufficient access in order to adjust the water balance after hand over, particularly if floor branch balancing valves are not used. It is therefore vital that each apartment is fully commissioned, tested, and documented as such, prior to final handover.

Comprehensive testing of the system is required to be undertaken, including reconciliation of each element’s performance with the original design. Sufficient testing should be undertaken to reliably verify performance of the following elements:

  • Air conditioning unit output;
  • Air balance;
  • Transmission loss on supply air duct work system, (air leakage and temperature pick up);
  • Infiltration through ceiling void;
  • Controls operation;
  • Condensate drain operation.

Testing of apartment’s systems is difficult due to space constraints, so results are often found to be inconsistent. Each test should be verified by an alternative means, eg measure airflow by the following methods until a consistent result is obtained (i) Balometer or anemometer scan of register; (ii) Differential pressure across unit and reconcile with manufacturers fan curve.

The level of testing to be undertaken on each apartment should be clearly detailed in the tender documentation and adequate allowance built in to the Tenderer’s proposal. In practice, time constraints often do not allow comprehensive testing to be undertaken on each apartment. In this case, KAE recommends that at least one apartment of each layout  type, and AC unit type, be fully tested to ensure; design parameters are correct, air conditioning unit capacities are correct  and in accordance with manufactures data. The remainder of the apartments must be fully commissioned in terms of condenser water flow rate and air flow rates.

The main items required to be tested and witnessed are air flow; water flow; cooling capacity:

 Air Flow

Assess and verify the supply air flow by a number of different methods, including at least  2 of the following:

  • Balometer or anemometer scan of register;
  • Anemometer scan of return air opening to the air conditioning unit;
  • Differential pressure across unit and reconcile with manufacturers fan curve.

 [Note: That it is normally not possible to undertake a reliable pitot tube traverse due to the lack of a suitable duct section.]

Cooling Capacity

This is best calculated local to the unit by measuring total air flow and air on and air off dry and wet bulb temperatures. Also measure refrigeration pressures, compressor amps and verify by reference to the manufacturer’s data.

Provide access and duct tapings to allow for temperature measurement.

Water Flow

Commissioning valves (complete with pressure tapings), easily accessible must be installed on all pipe work local to air conditioning units. Also install and undertake balance on floor branch valves to facilitate rebalancing subsequent to hand over if required.

Control Sensor Locations

The location of control temperature sensors is an important consideration.

Do not install:       In direct sunlight, or under the influence of local equipment heat gains;

Install in:                A representative area, typically 1.5m above the floor;

Number:

Typically one sensor/control panel is provided. Where two zones are installed consider master control panel/temperature sensor. Activation of either panel initiates its associated sensor.

[Seek client approval for more than one control panel, due to expense]

 

 

 

 

Aged Care – Biophilic Design

Aged Care – Biophilic Design

This post follows from my reading of the “14 PATTERNS OF BIOPHILIC DESIGN IMPROVING HEALTH & WELL-BEING IN THE BUILT ENVIRONMENT”, published by Terrapin.

The Terrapin document details the financial sense to design great buildings and details 14 criteria, that when achieved, result in a great building or space.

Patterns18

Biophilic design sits extremely well with Aged Care. Having undertaken many aged care projects and visited many project sites, you consider, “would I want to end up at this centre (must be an age thing)”.

Spend the money, comply with the ’14 Biophilic patterns, and the clientele will follow. Not only this, the aged need and benefit from great spaces, mentally and physically. For many aged, getting out of a centre and being safe is not easy. In these centres we should strive to bring that place of ‘serenity’ to them.

Following, are a few sketches which I hope you find interesting.

Sketch 1: Large Scale Plan showing Gathering/Communal Area I relation to accommodation.

 LargePlanLayout

Sketch 2: Biophilic Gathering Area

 BiophilicGatheringArea

Sketch 3: Biophilic Gathering Area – Section

 

Section1Biophilic

Sketch 4: Biophilic Gathering Area – Section

 Section2Biophilic

The table below contains excerpts from Terrapin document, with comments on engineering comment for patters 4 (Thermal & Air Flow), 5 (Presence of Water) and 6 (Dynamic & Diffuse Light)

Table: Biophilic Patterns, Check List

 Patterns1   Architect/Engineer    Score
 Patterns2 1  Yes, by Architect
 Patterns3 2  Yes, by Architect
 Patterns4 3  Yes, by Architect
 Patterns5 4 Yes. The space is designed as an open space. Air flow is encouraged by (i) natural wind paths, operable facades and openings (positive to negative flow) (ii) Thermally driven flow cooler to warmer (or higher density to lower density). When conditions are not suitable façade operates to seal/or partially seal. Cooling is achieved by evaporative cooling, thermal mass, sun control. When required mimic zone to have mechanical cooling. Cooling is also achieved by virtue of the height of the space and cool slab 10/10
 Patterns6 5 Yes, wet wall with pond provided. Adds movement, noise and free cooling (evaporative cooling). Also provides radiant cooling by surface temperature and position. 10/10
 Patterns7 6 Yes. Light patterns will be formed naturally via facades, shades, operable blade roof sections, plating etc. 10/10
 Patterns8 7 Yes. Space will mimic external conditions when required. Planting will be subject to autumn, winter, spring, summer cycles. 10/10
 Patterns9  Architect/Engineer  Score
 Patterns10  8 Yes, By Architect
 Patterns11  9 Yes, By Architect
 Patterns12  10 Yes, By Architect
 Patterns13  Architect/Engineer  Score
 Patterns14 11 Yes, By Architect
 Patterns15  12 Yes, By Architect
 Patterns16  13 Yes, By Architect
 Patterns17 Yes, By Architect

 

Summary

The “14 PATTERNS OF BIOPHILIC DESIGN IMPROVING HEALTH & WELL-BEING IN THE BUILT ENVIRONMENT”, published by Terrapin provides an excellent check list for great spaces.

If you need ESD and Engineering help, happy to assist.

 

Jorgen Knox PIC

Original Post Date: 20/02/2015

Contact: e: jorgenk@knoxadv.com.au, t: 02 800 33 100, w: KAE

Blog: https://engineeringbyjorgen.wordpress.com/
LI: au.linkedin.com/pub/jorgen-knox/27/a44/506/
 

What Your Mechanical Engineer Can Do for You?

 What Your Mechanical Engineer Can Do for You?

“Only an ESD consultant can do ESD”

Specialisation in Australia has led to a vast amount of knowledge and ‘know-how’ being wasted. Worse we are paying for another level of consulting, which can be very well handled by your existing core consulting team (Architect and Engineers).

To ‘draw that duct’, your mechanical engineer has at his fingertips, all the sites; climate data (including rain, solar, wind, temperature, humidity and so); has evaluated your fabric; considered shading, day lighting, equipment efficiencies; wall temperatures and colours and the like.

With this information all the ESD output needed for a project can be delivered. The only thing missing is that you have just asked them to only ‘draw a duct’.

Some Items you might want to ask for are detailed below:

Item
Is co-generation suitable?                       Gas Fired? Liquid Bio Fuel? Methane?
 Co-Gen Engine liquid bio-fuel
What size solar panels suit this site?
PV Chart
What shading is required to reduce Air Conditioning capacity (Façade Optimisation)?
 Window Shading Section  Window Shading Elevation
What is the average daylight level in a room? Is the room dark? Will lighting need to be turned on? SEPP 65 Day Light review
Room Daylight
Have I got interstitial condensation or surface condensation issues?
 Interstitial Condensation
Can I naturally ventilate that car park?
Can I remove all ductwork from a car park?

 

What air flow will I get with present openings…what openings should I have?
Single Stack Natural ventilation

SingleStackNatVent

 

Single Side Ventilation – two openings.

SingleSidedWindowVent

Air Conditioning Load reduction or load slowing by fabric selection (Façade Optimisation)
Energy (Heat) via Conduction Through Wall

CTSChart

 

Overall Load review (Sensible Heat)

CoolingLoadsChart

How much rain will fall on this site?
 PercipitationChart

 

 WaterConsumptionChart
What is the mass of the building?
Which AC System has the lowest running Cost?
 AHU1

 

 AHU2  AHUEnergyChart

 

What the prevalent wind direction?
  WindRose

 

 WindBarChart
Do I need air conditioning? How comfortable are occupants without air conditioning? Is free cooling an option?
 ConfortConditionsChart

 

What’s the pay back for; more insulation; LED lights; natural ventilation; shading devices; lighting control; co-gen, solar hot water; solar electricity, air con system 1 vs air con system 2; heat recovery and so on.
Can I use Geo thermal or ocean heat rejection to remove cooling towers?
How much energy is saved with a green roof?
Are zero carbon liquid bio fuels an option?
 liquid bio-fuel  Biogastank
Is gas fired air conditioning an option for my project?

In addition to the above most consultancies offer; Green Star, NATHERS, LEED, NABERS.

How did this happen?

Engineering, of old, was appreciated for good engineering and practioners focussed on excelling in the delivery of drawings and specifications.

As CO2 and energy relevance ‘took off’ in recent years, ESD companies saw a market. The engineers kept focused on drawing that duct.

Summary

The delivery of low energy products (buildings) is a team effort. To keep us on the ‘straight and narrow’, we have the BCA. To make it easier to see reward for our efforts, we have developed schemes where we get stars or numbers or both.

A modern mechanical engineer has all the necessary skills to deliver and assist in delivering low energy products. Often no additional fee is required.

As ever, it’s down to individuals. Find someone who has a drive and passion and technical ability to deliver low energy products and that’s your best choice.

Author: Jorgen Knox

Jorgen Knox PIC

Original Post Date: 19/02/2015

Contact e: jorgenk@knoxadv.com.au, t: 02 800 33 100, w: KAE

LI: au.linkedin.com/pub/jorgen-knox/27/a44/506/

 

 

Apartment Air Flows – Is it All Academic?

 Apartment Air Flows – Is it All Academic?

Last Updated 25/9/2016

This post discusses; why outside air is required and how getting the right air flows is crucial in an apartment. This is all quite simple and yet often overlooked resulting in poor apartment amenity and higher energy consumption.

Outside Air

Outside air is required for the following:

  • It’s a code requirement as per the NCC for occupants. Outside air is required for occupant’s health and well-being. This is for breathing and odour control.
  • Its required so exhaust systems work
  • Its a code requirement as per NCC referenced standard AS1668.2 (2012)

AS1668.2 Excerpt

Government of Western Australia Department of Commerce, Ventilation in buildings – Bulletin

  • Where gas heaters are used for heating its required for combustion.
  • Ventilation removes moisture and thus condensation issues.
  • Ventilation removes VOC’s

Moisture levels within buildings are often higher than outdoors. The main cause of high indoor moisture levels is the generation of warm moist air by domestic activities.

Heaviest loads are produced by:

  • cooking
  • bathing/ showering
  • clothes drying
  • high occupancy
  • high indoor plant concentrations
  • uncontrolled moisture ingress.

Excerpt above from The BCA Information Handbook: Condensation in Buildings

Where moisture lands on cool surfaces (below the dew point temperature of the moist air), water will come out of suspension and form on the cool surface.

VOC’s: Non removal of contaminants produced by outgassing of some types of building materials, volatile organic compounds (VOC), can cause discomfort (sick building syndrome).

So outside air is required. It cannot be avoided.

The problem with outside air in today’s well insulated and well-sealed buildings is that natural air intake is not readily achieved. Designed solutions are required.

Also with the drive for energy efficiency the introduction of outside is an energy issue (if you intend to have a controlled environment (heating and cooling). Also if outside air cannot be naturally delivered or induced then mechanically supplied or mechanically induced air will be required which consumes energy (fan power).

Air Flow Amount

The amount of air for an apartment for condensation control and VOC reduction is not easily found in documentation. This is because it all depends on the amount of moisture vapour produced and the surface temperatures on the various building elements.

The graph below details some residential moisture rates.

Water Vapour

Source: http://www.labenvironex.com/commercial-industrial-moisture-sources-houses.html

From the above it’s not hard to see how 18 litres of water per day can be produced in a domestic situation.

The following chart below indicates circa 40 l/s of outdoor air is required for a house.

Moisture Input

Source: http://www.labenvironex.com/commercial-industrial-moisture-sources-houses.html

The figure of c. 40 l/s is only a guide as it is subject to many many variables including outdoor condition of the air (moisture and temperature, moisture production, internal room temperatures and fabric and construction types.

Typically when an apartment is occupied and kitchen exhaust is directed to outside and with intermittent operation of other exhaust systems air flow rates are well in excess of the 40 l/s indicated above.

The UK’s Building regulations, Part F1, requires the following ventilation rates:

UK Building Code

Outside Air Quantity – Occupants

If the air supply is via a filtered outside air system (could be via the air conditioning system), then 7.5 l/s per person of fresh air is required.  The current ventilation rate of 7.5 L/second/person is designed to maintain levels of indoor carbon dioxide exhaled by occupants below 1000 ppm. This carbon dioxide level is used as a surrogate for body odours unacceptable to 20% of visitors entering an occupied space.

As an alternative (if the air is not mechanically delivered) part F of the BCA allows for air to be supplied by operable openings. The operable opening should be sized at 5% of the rooms floor area.

If a room has no operable opening it can take air from an adjoining room. Refer to NCC part F for details

Where openings cannot be used, for example in high noise locations where opening a window will cause un acceptable internal noise levels, air must be provided by alternative means.

The alternative systems include; delivering outside to the apartment’s air conditioning system; by providing acoustic trickle vents where the air is drawn in via an apartments exhaust systems; acoustically designed supply air systems or delivery of outside air by the apartments corridors.

Trickle Vents:

Silencer air intake

http://www.silenceair.com/silenceair-products.html

519[1]

http://www.greenwood.co.uk/range/15/acoustic-vents.html

SCW-N_Install_image_2[1]

http://www.proctorgroup.com.au/natural-ventilation/

Corridor Make up Air, Re-purposing of Relief air Shafts (Buildings > 25m)

Where the development requires stair pressurisation the associated relief air shaft can be utilised to deliver outside air to each floor. Air to each apartment is then via fire dampered air intake (typically a 300 x 200 intumescent fire damper with acoustic flexible is utilised).

Part Schematic (showing Corridor Outside Air System)

lobby-outside-air

Outside Air Quantity – Exhaust

Most apartments have the following systems:

  • Toilet Exhaust
  • Kitchen exhaust
  • Laundry Exhaust

Where bathrooms and laundry’s are on an outside wall, with an operable window, then natural ventilation can be used. Interestingly domestic kitchen exhausts do not require venting to outside and inactivated recirculating car bon filter can be used. In these circumstances the only outside air to an apartment will be that required for occupants.

Where the systems are mechanical and ducted to outside then fresh air equal to the exhausted air volume will be required.

  • Toilet Exhaust 25l/s
  • Kitchen exhaust 150 l/s (subject to hood supplier)
  • Laundry Exhaust 40 l/s

If all systems operate together this is 205 l/s of fresh air required, vs say for a 3 bed apartment (3 x 10l/s/person) 30 l/s for occupants.

Note: It would be typical to use a diversified air flow.

Room air flows

If no means to allow air into the apartment is provided, then the exhaust systems will not work effectively and cause undue fatigue and early failure of the fans.

As the fans operate and the apartment becomes more and more negatively pressurised it is not uncommon for make-up air to be drawn from adjacent apartments via wall cavities and poorly installed electrical services and the like. You will soon know what next door is having for dinner.

So outside air is required for occupants and for exhaust systems (AS1668.2 2012 requirement) to work. If heating or air conditioning is provided, then this outside air needs to be accounted for in the sizing of this equipment.

Energy Reduction

In order to reduce energy for outside air consider the following:

  • Recirculation only kitchen hoods (not recommended for moisture control)
  • Independent fan systems with timers (Minimise run time)
  • Introducing outside air for exhaust systems locally.

Note: This can provide a good result. If the make up air is local to the exhaust (allowing for scarification) then the outside air load can, in part, be removed from the air conditioning unit cooling size (This could be around 1kW r). Careful attention to design is required due to the partial pressures of room air and make up air, resulting in vapour moving rapidly into low air pressure regines in an apartment.

  • Heat Recovery systems.

Note: based on the intermittent usage of ventilation systems and coincidence of the air conditiong operating at the same time, the pay back on residential heat recovery can be very long.  A recent study found pay backs in excess of 69 years.

Heat Recovery – outside air to room air

Heat Recovery

Where gas fired room heaters are installed consideration should be given to a exhaust gas to outside air intake heat exchanger….this is a great opportunity for a gas fire supply!

Hotel Example

A number of hotel organisations have a ducted outside air system to each hotel suite.

The outside air is delivered to the suite only when occupants have rented the suite. The air is off (thus saving energy) when the suite is un-occupied. Typically the room supply air is activated a few hours before guests arrive to flush the room and then turned off a few hours after cleaning.

It’s All Academic

In Australia, it is not typical to pressure test our buildings. This is done in other countries to prove the air tightness of each space.

Thus designing for exact air control for occupant health and wellbeing and lower energy costs may be a waste of time. Air flow into an apartment may be excewssive or minimal depending on the construction of the building and jointing details on windows and doors etc. On a leaky building, the air conditioning capacity (where installed) is often struggling to maintain conditions.

Pressure testing of building In my opinion should be a mandatory item in the BCA.

Air Conditioning Supply Air

Supply air to a room = relief air from a room.

For example if you supply air into a closed (door closed) air tight room the room would become positively pressurised and quickly no more air will be delivered to the room, thus no cooling or heating.

Relief air can be provided by a number of methods including:

  • Relief air device/grille
  • Door Undercut

A door undercut is often used. This is OK, but if the bedroom is large and has solar loads, then the door undercut will quickly not be viable.

Air Flow 1

Diagram 1: Door closed, Preventing air Entering the room

Air Flow 2

Diagram 2: Door Open Allowing Air into the room

Air Flow 3

Diagram 3: Air Flow in occurs due to designed return air grille

Air Flow 4
Diagram 4: For low air flows (small rooms) a door undercut can be used

Air flow through an under cut:

Say 25mm height (above carpet) x 900mm door width and 1m/s = 22 l/s. This would only suit a 4m2 room! The 1m/s is a rule of thumb and provides a low noise and low resistance solution.

Services Available

Where control of humidity is vital various calculations involved with humidity and condensation control (surface and interstitial) are available.

  • Fabric Analysis including:
    • U Value Calculation
    • Surface and interstitial condensation review
    • Thermal bridging
  • Thermal heat Loads
  • Energy Consumption
  • Air Conditioning Design
  • Ventilation Design

Author: Jorgen Knox
Contact: e: jorgenk@knoxadv.com.au, t: 02 800 33 100, w: KAE
Blog: https://engineeringbyjorgen.wordpress.com/
LI: au.linkedin.com/pub/jorgen-knox/27/a44/506/

Greening our Buildings, Literally

Greening our Buildings, Literally

This post discusses green spaces in urban areas and proposes, any natural land we displace with a development, be exactly replaced or re-dispersed on the same development. This is simple and clear and doable and not a ‘more points’ in a ratings scheme.

What right have we?

Man creates massive urban areas. Soft areas become hard areas and species are pushed out of the way, or worse. Green areas (vegetation, soil, eco systems etc.) are replaced with a built environment.

A tad arrogant. Hey, but we are humans.

There are many natural cycles that occur that we are aware of, and I’m sure many, many, more we are not. Urbanisation can dramatically modify these natural cycles. The global attack on these natural cycles is not yet fully understood.

The water cycle below is certainly one such natural cycle affected by urbanisation.

Water Cycle

Other natural cycles include the carbon cycle and the nitrogen cycle.

What can be done?

In truth, with our population growth, not a lot in the long game. However ‘going vertical’ will reduce our impact on land surface area and allow us more easily to replace that surface area on and within our new buildings.

As a starting point we could consider the following ideas.

Replace displaced

Any site prior to being urbanised must be accounted for, square meter by square meter, including oxygen producing trees, grass and so on. This natural green environment must be replaced as part of the development. A new role for our surveyors and quantity surveyors!

In practical terms this is achieved by green roofs (with deep soil), perimeter gardens on multiple levels, internal sun lit green courtyards, green walls and so on.

Green Roofs

Re Connect

Prior to a new development water and wildlife were provided with full access to the landscape. A new development is a ‘brick wall’, breaking and separating habitats and eco systems. Green corridors through our sites should be provided, allowing connection of green spaces.

In cities, we provide pavements for human connections. With some simple thinking even our cities can link our parks with green corridors (could even share with humans with a path), allowing animal and insect connection.

In Sydney we are building a new connection between the city and the Barangaroo area of the city. Great for humans, but so short sighted for our wildlife. The incorporation of green, deep verges within this connection, together with skylights for underground areas would have provided a natural connection corridor.

Bike lanes, tram ways, think green ways.

Green way

Green Corridor 2

Pay Back ($)

Ahh some of you are heading straight to the dollars. What will this cost? We can’t afford it. Well that’s one way of looking at it. Another way is back to the top of the page…what right have we. If we take away the natural environment, we need to pay for it or as I’m advocating re-disperse it in exactly the same quantity.

With a few more seconds of thought you can consider the big picture cost (not just the quick up front cost). You can now place a value on the greening of your buildings. There are schemes available to calculate the financial benefit to the community of your green building. Given these buildings will be around for decades, this is a lot of money added to the community. If I were a councillor reviewing a development this would be near the top of my list on an approval review.

 Benefits

Firstly its simply the right thing to do, but there are countless other benefits, including:

  • Un-sterilizes our world
  • Wild Life Increase
  • More Bees
  • Lowers city temperatures
  • Reduces dramatically earth sun-light reflection
  • Slows water run off
  • More oxygen
  • Less CO2
  • More areas to relax
  • Reduces air conditioning costs
  • Reduces glare
  • Provides areas for crops/fruit trees etc
  • Aesthetic and psychological benefits (less doctor visits)
  • Improved human health (less doctor visits)
  • Green walking/running tracks
  • Car free zones
  • storm water  runoff  reduction
  • carbon sequestration and  storage
  • Provision of shade
  • Human interaction zones
  • Increases property values
  • Air quality improvement
  • Species diversity
  • Increased tourism

Development Impact

Greening of our developments, literally, will require, for some, a reset on our present concept of building form and function.

It is likely building will need to be taller. This is simply inevitable anyway, given our human population growth. Reducing building heights to old DCP’s is just daft and planning departments are just slowing the inevitable. What should be happening is allowing building height increase and ensuring light to green spaces and green corridors. On the assumption global warming is real, we are going to want a lot more shaded spaces to move between in the future.

Additional height will be required to accommodate (structurally) mid level(s) of deep soil areas and deep soil roof gardens. Loss of lettable /saleable areas, to green areas, will need replacement areas to keep developments profitable, thus upward pressure (more levels).

Building shapes will change to accommodate mid level green areas allowing sunlight.

On smaller projects traditional roofs will change from a cheaper pitch construction to concrete roofs to allow for deep soil gardens.

Building Usage will change. Commercial ‘parties’ will move to commercialising these green areas. Roof top gardens will become garden centres, sporting facilities, with gym facilities below, wedding venues and so on.

Practicalities

As ever, words, words and words. To get this happening prior to any global catastrophic events will require legislation. Get it into the BCA (Building Code of Australia). It’s also down to our planners to organise an Australia wide set of planning rules to drive the greening of our buildings.

Author: Jorgen Knox

Original Date: 26/08/2014

Contact: e: jorgenk@knoxadv.com.au, t: 02 800 33 100, w: KAE

Blog: https://engineeringbyjorgen.wordpress.com/
LI: au.linkedin.com/pub/jorgen-knox/27/a44/506/

 

Data Centre Cooling – Simplified

Data Centre Cooling

This post discusses cooling (air conditioning) of your data centre.

What is a Data Centre?

Data centres can be small or massive. In simple terms they are rooms (or data halls) where you put your IT equipment.

As the importance, to you, of your data centre grows, you start to consider:

  • UPS
  • Air conditioning
  • Failure
  • Supply quality

Air Conditioning

As you group more and more equipment into a room, the amount of heat rises and so does the temperature.

The IT equipment has recommended operating temperatures for optimum operation and for extended life. These recommendations dictate the temperature and humidity the air conditioning system needs to maintain in your room (See also ASHRAE conditions).

At this point, it’s simple, you need cooling. Often (historically) the entire room was kept at c. 24 Deg C.

ASHRAE

Recent design guidance by ASHRAE has provided a set of conditions that are acceptable for data centre equipment. These conditions allow for your room(s) to be maintained at higher temperatures.

In essence this just saves you a lot of air conditioning. The upper end of acceptable conditions is now 27 Deg C (supply air onto racks).

In summary ASHRAE have come up with the following requirements; a stable environment of (18°C to 27°C) with moisture between (5.5°C) dew point and 60% relative humidity with (15°C) dew point.

Delivery of cold air

The physical constraints of your room often dictate the method of getting cold air into the space. Air can be supplied via under floor plenum or ceiling located ductwork and diffusers.

Some systems employ cooling banks within the racks themselves, either DX or chilled water, with fans drawing air through each cooling bank. These systems are not discussed in this post.

High Level Supply – General

High level supply is normally non preferred. This is because typically, the air is delivered to the room at say 10 to 12oC with a large portion of the room being fully treated.

 High Level Supply – Full Mixing

Typically the air mixes with the entire room load and a mix condition is achieved at the rack equipment. This method is energy intensive.

High level Supply

High Level Supply – Hot Isle/Cold Isle

With this method, the aim is to supply cold air to the inlet side of the racks, with air being discharged to the warm isle side. The warm air is then removed via a return air duct. This method is an improvement on full mixing in terms of energy consumption.

 Under Floor Supply

This is the preferred method of providing cooling for many data halls. This is for three main reasons, namely; it keeps overhead areas free for wiring, cable trays etc;  allows for supply air at low level, local to racks, thus avoiding mixing of supply air with room air, as occurs with high level supply and allows installation of racks without constant need to modify ductwork or grilles.

Under floor supply has many issues that need resolving including:

  • Limitation of supply air being delivered under the floor, with typical un-ducted throws to circa max 20m.
  • Floor leakage
  • Poor air flow control with difficulty experienced in commissioning floor grilles for correct air flow
  • Poor air flow for partially occupied data rooms resulting in multiple AHUs being run to achieve required air flows.

Central Plant

So, we need to cool the air in the room due to the heat load from the racks. This means air conditioning.

There are many new systems around at the moment professing to be the best solution for air conditioning your room. Most are really plugging the low air conditioning PUE (Power required for air conditioning vs IT power load). In general the quoted PUE’s are all very similar.

Don’t be ‘sucked in’ to quickly, when looking at these low air conditioning PUE solutions. Basically the low PUE’s are being achieved purely because they can provide a lot of cooling by using low temperature outside air. Further these manufactures are selling a product, a packaged product and decanting some of their parts is not in their sales interest. No slight intended here, there making a product for sale, we can buy it or not.

Traditionally the large data centres provided cooling by central plant chillers serving in room (or corridor Located) close control air conditioning units (CRAC Units).

CHW CRAC

Chillers were used as these, combined with a cooling tower, had the highest COP (Co-efficient of performance). Chilled water made at the chillers was then pumped to the Crac units, where the return air was drawn over the chilled water cooling coils to be cooled before being supplied back to the underfloor plenum. The only thing missing in this scenario is not utilising the free cooling when the outside air was cold enough to provide ‘free’ cooling (instead of the chillers). With the new ASHRAE conditions allowing for warmer data hall supply air temperatures, allows for even more free cooling availability from the outside air. Thus, this type of system has lost some favour. See later for free cooling chillers.

The main systems under consideration at present are:

  1. Direct Outside Air System, With Adiabatic Cooling + Air Cooled Chiller
  2. Indirect Outside Air System, With Adiabatic Cooling + Air Cooled Chiller
  3. Enhanced Crac unit, with free cooling cycle added in.

All systems purport very low PUE’s.

Simplified Review.

  1. Direct Outside Air Systems

Example Manufacturer: Trane

Trane unit

These systems, are in simple terms, a large air handling unit comprising:

  • Return air connection
  • Outside air connection, with motorised damper
  • Mixing plenum
  • Filters
  • Spill air fans
  • Air to Air heat exchanger with enhanced cooling due to wetted surface
  • Adiabatic cooler
  • Cooling system (coils, compressors and the like)
  • Supply air fans

Advantages

  • Utilises free cooling by using outside air, when low outside air temperatures.
  • Utilises free cooling by removal of latent heat when outside air wet bulb less than indoor wet bulb.
  • For heat transfer uses air directly to space, thus avoids minor loss of efficiency, when using an indirect air heat exchanger.

Disadvantages

Very large unit. Needs careful positioning. Significant air flows required for scavenged air fans, spill air and outside air intake.

Large fan power losses due to:

  •            spill air fans
  •            scarification fans
  •            Main supply air fan overcoming resistance of ductwork, heat exchanger and the like
  • Loss of control of air temperatures and humidity due to possible leaky outside air dampers and the like.
  • In outside air mode, relies purely on filters to remove any external contaminants. This needs consideration in industrial areas, bush fire areas, high insect areas and the like.
  • High water usage, thus on site N+1 water supply required.
  • Room humidity control likely to be difficult, with air direct from outside.
  • As the filters are subject to outside air, regular cleaning will be required to avoid energy loss due to fans overcoming dirty filter pressure drop.

In summary these units are designed to maximise the new ASHRAE acceptable conditions in a data hall. As these new conditions, in simple terms, are warmer, cooling energy is saved by 1, having to do less cooling, 2) ability to use free cooling for a large proportion of the year. The disadvantages are that all the energy saved is then significantly eroded due to having to supply large quantities of air to the data hall, against significant internal resistance.

  1. Indirect Outside Air System

Example Manufacturer: Munters (Oasis)

Munters Section

Munters Oasis

These systems are similar to the direct outside air units, except as the name suggests, no outside air enters the room.

Room air is continually recirculated through the unit and cooled via outside air which is drawn over the Munters heat exchanger. To increase free cooling, Munters also spray the heat exchanger to increase heat loss.

Advantages

  • Utilises free cooling by using outside air, when low outside air temperatures.
  • Utilises free cooling by removal of latent heat when outside air wet bulb less than indoor wet bulb (likely not as efficient as the direct outside air system).
  • Air filters are circulating room air only, thus less dirt resulting in less fan energy
  • Reliance on modulating dampers for outside air control (and possible damper leakage) does not occur (no dampers).
  • No Issues with quality of outside air E.g. Brushfires

Disadvantages

Very large unit. Needs careful positioning. Significant air flows required for scavenged air/spill air fans.

Large fan power losses due to:

  •               Scarification/spill air fans
  •               Main supply air fan overcoming resistance of ductwork, heat               exchanger and the like
  • No outside air supply to the data hall. A supplementary unit is required for this.
  • High water usage, thus on site N+1 water supply required.
  • Room humidity control likely to be difficult, as no moisture is added to the room. Thus for low humidity control a supplementary AHU with active moisture input will be required.

In summary these units are, again, designed to maximise the new ASHRAE acceptable conditions in a data hall. As these new conditions in simple terms are warmer, cooling energy is saved by 1, having to do less cooling, 2) ability to use free cooling for a large proportion of the year. The disadvantages are that all the energy saved is then significantly eroded due to having to supply large quantities of air to the data hall, against significant internal resistance. These units are theoretically less efficient that the direct outside air systems (heat exchanger efficiency loss), but counteract this loss with less fan power, due to filtration reduction, damper leakage etc.

Improvements – Direct and Indirect Systems

The direct and indirect systems are fairly new and are step, as a result of the Ashrae conditions, to provide a neat packaged air conditioning system. Fit and forget.

Improvement Ideas

Consider using water cooled chillers for supply of chilled water to the cooling coils. With modern chillers it is likely that much better COP’s can be achieved than with the manufacturers DX systems. Further modern chillers can be supplied with free cooling systems using a heat exchanger and the outside air to pre cool the chilled water prior to compressor operation. In addition the chiller refrigerant can be air cooled, without the compressor, with low outside air temperatures.

During modulating outside air mode, with the direct outside air systems, consider passive one way flow relief dampers in the walls of the data hall. This will avoid the fan power associated with dragging the entire air backup the AHU only to be discharged by mechanical fans to the atmosphere.

Consider a passive thermal floor with an underfloor supply air system. The slab is sitting atop earth at say 17 oC. With the correct concrete selection heat loss to the ground can be encouraged, thus providing free cooling.

Consider and active thermal slab. Here chilled water pipes are embedded during the slab pore. Chilled water is delivered to the slab to cool it. This provides a significant amount of cooling and reduces the amount of air being delivered by the fans.

  1. Enhanced CRAC unit System

Example Manufacturer: Liebert

DSE unit DSE with free cooling

These systems, in simple terms are packaged DX split systems.

Their main benefit, on the energy front, is that they are located in the room (or close to) and thus have small fans to deliver the air to and from the room. This feature alone greatly assists this technology as compared to the large fan power associated with the Direct and Indirect air systems, discussed above.

Refrigerant is a great way to transfer heat, with refrigerants able to transport per unit volume circa twice as much energy as water and circa 40 times as much heat as air. Thus keeping air and to a degree water movement out of the ‘picture’ saves a lot of energy.

The ‘enhancement’ is by getting some free cooling of the refrigerant from the outside air, without compressor power. Liebert call it the “EconoPhase economizer”.

DX (Direct Expansion) cooling uses a refrigerant to take heat out of the room air and then get rid of it to the outside air. The refrigerant is maintained, in simple terms, in two states; a vapour and a liquid.

The refrigerant in liquid phase picks up the room heat, adding energy, which causes the refrigerant to expand into a gas and a higher pressure, this gas then has the heat removed by blowing air over it (within a finned tube) and the refrigerant reverts back to a liquid. Assisting this process is a compressor which provides the compression of the refrigerant to make it easy for heat to be picked up from the room air and an expansion valve with creates a pressure change allowing for control to the liquid state.

The Liebert ‘EconoPhase economizer’ is basically a set of tubes, with a liquid refrigerant pump, that pumps the liquid refrigerant back to the indoor unit, by passing in effect the compressor. The colder the outside air, thus the colder the refrigerant liquid is, the less compressor work required, thus less power consumed as the liquid refrigerant pump uses a lot less energy than a compressor.

Refer to Liebert Technical Manual, for detailed description of operation: http://www.emersonnetworkpower.com/documentation/en-US/Products/PrecisionCooling/LargeRoomCooling/Documents/SL-18920.pdf

Advantages

  • Known technology
  • Avoids massive air flow movement with associated fan power costs
  • Can be dual cooled (chilled water coils and DX coils)
  • No direct outside air
  • Close control (temperature and humidity control)
  • Low spatial requirements (when combined with a chilled water system – removes dry air cooler).
  • No water consumption

Disadvantages

On the assumption that the quoted PUE’s are correct, there are few disadvantages with this system.

  • Low fan static ability
  • Need for outside air via separate unit.

Improvements – Enhanced CRAC unit System

Improvement Ideas

Where dry air coolers are used for heat rejection, consider a micro mist spray to increase the heat transfer process.

Client Review

Before considering new air conditioning for your data hall the following should be considered:

Undertake report to verify the best cooling solution. The report should consider:

Systems

  • Direct Air Systems
  • Indirect Air Systems
  • CRAC DX Splits
  • Chilled Water vs DX

Equipment

Review of major plant items and their efficiencies

  • Fan Motor Efficiency
  • VAV fans and turn down ability
  • Compressor size and numbers and are they infinitely controllable to match cooling load.
  • Damper Air Tightness
  • Duel circuit cooling system or not.

Passive Free Cooling

  • Slab Cooling
  • Air Intake to avoid SOL air Temperatures
  • Passive Spill Air
  • Location of plant to avoid supply and return air ductwork air flow pressure loss
  • Roof, wall thermal loads (make zero).
  • Air tight (make air tight)

Water

  • Water usage and water costs

Spatial

  • Size and weight of plant
  • Requirements to avoid heat short circuiting
  • Chillers to avoid large DX heat rejection plant

Reliability

  • Proof of reliability
  • Proof of failure rates
  • Proof of maintenance ability

Risks

  • Water loss
  • Damper Leakage
  • Bush Fires
  • Refrigerant loss
  • Water Treatment
  • Filter cleaning
  • Heat Exchanger Cleaning

Controls

  • Fully packaged controls with high level interface
  • No controls (relies on separate BMS)
  • Open protocol language, match your requirements

Installation

  • Time to install
  • Ease of replacement
  • Spare parts

Life Cycle Costing

  • Capital Cost
  • Energy Consumption
  • Verified efficiency data for your location
  • Replacement cost
  • Maintenance costs

Practicalities

So you have spent all this money, got a ‘you bute’ data hall full of air conditioning and you’re not happy. Why? Some of the items below could be why:

My data hall is too hot: This could be down to many things (wrong heat loads, fabric heat gains not accounted for, incorrect unit sizing and so on). Discounting all of these it is likely you have not got hot isle containment, thus the return air is getting up to say 39 oC and thus so is your entire data hall. To solve this retrospectively you will need to install hot isle containment. If this is not possible you will need to throw away energy efficiency and supply air at say 18 oC.

I have to run all my air handling units to get the air flow out of the floor grilles: Another classic. This can be down to many reasons (leaking floor tiles, leaking supply air system and floor void, incorrect fan selection, floor air supply flow patterns and turbulence). Discounting all of these it’s likely that you have designed your data hall for a future full occupancy scenario and you have one rack sitting in the room. So the cooling load only equates to a partial unit. Operation of this unit alone will not create enough pressure in the floor plenum to get the required air out of the required floor grilles. There are air flow management solutions (not discussed in this post).

I lose all my air conditioning on a power interruption: You probably forgot to think about a few things, including; auto change over switching on each AHU or a whole MSSB (Mechanical Services Switch Board) or the AHU controls, on loss of power and then on power resumption, don’t know what to do and require a manual restart.

My air conditioning PUE doesn’t seem right: This is important as you have ‘spent up’ significantly having a report written to select your air conditioning and the manufacturers have quoted you all sorts of amazing figures. So, get the electricity and water consumption to each AHU monitored and logged against IT load. Also monitor Stevenson screen air temperature and humidity as well as actual air intake conditions.

Sign up your supplier for a performance guarantee. Make them responsible for ensuring their AC units are working correctly, with sensors calibrated, VSD fans ramping up and down correctly etc.

Commissioning & Monitoring

I’ve ended this post with commissioning and monitoring. All the above can be compromised by lack of commissioning an don going monitoring. It is strongly recommend a commissioning consultant is brought on board to ensure required commissioning is undertaken and proven.

The consultant would liaise between the designer, the equipment manufacturers, the installers and client to set up a required commissioning plan and ensure that each commissioning test is undertaken.

Continuously monitoring of the energy used by the racks and the air conditioning energy, together with the rack supply air temperature is vital. Depending on the equipment in each rack, more energy may be consumed by the racks due to ASHRAE high air on temperatures (27 oC). Typically this is due to the equipment fans operation at higher speeds and for longer. So all that thought and design and free cooling calculations by using warmer supply air temperatures to get greater efficiencies from the cooling system may in reality not be achieved. It is recommended cooler supply air temperatures are used in the first instance (say 24 oC) and a slow temperature increase undertaken, with energy verification at each step rise in supply air temperature occur. If the power usage goes down, try another supply air temperature increase and so on.

Also monitor your equipment failure rate at each temperature increase. Equipment failure increases with temperature.

Further information provided on request.

Author: Jorgen Knox

Jorgen Knox PIC

Original Post Date: 19/01/2015

Contact: e: jorgenk@knoxadv.com.au, t: 02 800 33 100, w: KAE, LI

Blog: https://engineeringbyjorgen.wordpress.com/