Centralised Systems – Water Cooled
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Water sourced (Condenser water) packaged units serving each apartment and connected to a central air cooled (or water cooled e.g. cooling tower) condenser water (CW) heat rejection and distribution system. A central CW heat rejection and distribution air conditioning system is suitable for the following situations:
- Where the building height and subsequent vertical separation between indoor and outdoor units exceeds the refrigerant piping capabilities of VRF systems with condensing units located on the roof.
- Where the available roof plant area is too small to install individual VRF (or similar) systems.
- Where louvred plant areas for individual VRF (or similar) systems on each level of the building is not suitable.
- Where it is desirable for a majority of the apartment’s air conditioning energy consumption to be directly metered at the apartment’s metered electrical distribution board, unlike a central CHW system or VRF/VRV systems.
- Where requested by the Developer.
Generally two (2) or more CW heat rejection machines, or dry coolers, and three (3) CW pumps are installed for each building to provide the associated building’s heat rejection capacity whilst providing an agreed level of redundancy if one dry cooler fails.
Refrigerant R410a is currently utilised by all reputable WSPU manufacturers.
Heating is generally provided via reverse cycle WSPU (with boiler heating top up at roof plant) or less commonly via electric heating elements at the WSPU.
The system arrangement includes:-
- Air cooled dry cooler/s consisting of heat rejection coils, discharge fan/s and associated electronics, with optional drive (motor) technologies available for each component for increase energy efficiency.
Dry cooler (image courtesy LU-VE).
- Multiple WSPU, each consisting of a fixed speed compressor/s, condenser vessel, evaporator coil, electric heating element, supply fan/s, and associated electronics. In-ceiling ducted WSPU’s are available from limited manufacturers only and other types such as wall mounted are not available.
Indoor in-ceiling WSPU (image courtesy Temperzone).
- Pumps, CW piping, valves, an expansion tank and water treatment system for distributing CW between the WSPU and the WSPU throughout the building.
- A CW thermal energy meter for each apartment (may possibly be omitted – refer below)
- A building management and control system (BMCS)
Unlike VRF systems, a CW distribution system can be designed and installed to suit almost any building height or configuration.
As the refrigerant compressor is located within the indoor WSPU instead of the outdoor condensing unit (VRF) or chiller (CHW generation), the depth of the indoor unit is increased, and the noise generated by the indoor unit within the apartment is considerable higher. Increased ceiling void allowances and in-ceiling attenuation may required with this system arrangement.
Similar to VRF systems, apartment air conditioning control functionalities are managed at a control panel associated with each WSPU. However each control panel is connected to a BMCS which operates the dry cooler/s, CW distribution and/or electric heating elements based on cooling or heating demand from each WSPU.
The BMCS may also be required to collect data from CW thermal energy meters installed at each apartment and apportion the central CW heat rejection and distribution system’s power consumption based upon each apartment’s air conditioning usage. The BMCS automatically generates air conditioning CW energy bills for distribution to each apartment owner / investor / occupier. However as the energy consumed by the central CW heat rejection and distribution system is relatively small compared to the indoor WSPU’s, the Developer may decide to delete metering of CW and absorb the ongoing costs of the central system for simplicity.
The air cooled central CW heat rejection and distribution system requires ownership, operation, maintenance and ultimately replacement to be managed as a common property facility by the body corporate. This may include entering into an air conditioning CW energy supply agreement with each apartment owner / investor / occupier, with the bills distributed and associated monies collected as described above.
Each individual WSPU is connected to the associated apartment’s metered electrical distribution board, with the energy consumed by the WSPU included in the apartment’s overall electrical energy consumption. Therefore for WSPU energy consumption, the apartment owner / investor / occupier is required to enter into a negotiated energy supply and billing arrangement directly with the apartment owner’s / investor’s / occupier’s electrical energy distributor of choice, and not with the body corporate.
An air cooled central CW heat rejection and distribution system can be utilised to serve common area air conditioning systems through connection to associated WSPU’s.