Water Cooled VRF SYSTEMS – Water to Refrigerant (MULTIPLE APARTMENTS)
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General
These systems have a similar external VRF condenser systems described for large VRF refrigerant only systems. With this system, cooling water from a closed circuit cooling tower or open type cooling tower is delivered to on floor condensing units. Refrigerant R410a is used between the condensing unit and BC unit (16 port or 8 port). Refrigerant R410a is further used between the BC and each indoor AC unit is utilised between the on floor heat exchanges and the indoor units.
The condenser water (CW) range has to be maintained between 10 C & 45 C. In the winter, if the condenser water drops below 10 C, a boiler is required to inject heat into the condenser water. The requirement for defrost is avoided in this case. Except for the heat rejection equipment, the remainder equipment can be housed inside the building, an advantage if the ambient atmosphere is corrosive, such as located at close proximity to the ocean.
This system is used when:
- Building heights exceed maximum pipework allowable heights
- Maintain refrigerant volumes below standards.
Typical On Floor Condensing Units (CU)
These water cooled (condenser water) condensing Unit modules are located in on floor plant rooms (un ventilated, for Mitsubishi CU’s).
Refrigeration pipework runs from these units to the indoor units.
- Water flow volume control function
- Ventilation not required
- Can send signal to change condenser water flow rate to save energy.
Water Cooled VRF system advantages are as follows:
1) Condenser unit plant space can be provided inside the building. Typically in a cupboard in the lift lobby area for example.
2) Certain manufacturers provide a minimal foot print, therefore the space requirement is minimal.
3) Because the condenser units are located on the same floor that’s being air conditioned, the pipe run is minimized, hence reduced power consumption.
4) The reduced refrigerant pipe run and therefore reduction in the refrigerant amount helps to offset the cost increase due to the requirement of a condenser water circuit.
Capacity
In summary modules are added to a plant room to achieve connection to required no. of indoor units.
Pipework Limitations
The pipework height is only limited by the pressure rating of the heat exchangers.
The condensing units have a 2 M Pa rating (c. 20 bar, c. 63 floors of water at 3.2m FF).
Controls
Apartment air conditioning control functionalities are managed at a control panel associated with each fan coil unit. However each control panel is also connected to a BMCS which operates the heat exchanger and cooling tower.
See Ownership & Billing, below for more control requirements.
Heating & Cooling: Two systems types are available, namely; cooling only and reverse cycle.
Cooling Only
Cooling only systems are suitable where heating of a conditioned space is not required. This is generally not the case.
Reverse Cycle
Reverse cycle systems have the ability to cool and heat, however only simultaneous cooling or simultaneous heating can be accommodated by all fan coil units connected to a single condensing unit. Therefore all rooms within an apartment served by a reverse cycle system can only be provided with either cooling or heating at any one time.
Heat Recovery
Heat recovery systems utilise branch selector units within the refrigerant piping to allow independent cooling and/or heating from any fan coil unit connected to a single condensing unit. Therefore individual rooms within an apartment can be provided with either cooling or heating at any one time
Ownership & Billing
The closed circuit cooling tower (or open circuit cooling tower) and pipework to on floor Condensing unit and BC’s form part of a common system, connected to the developments house power. Check with manufacturer and AS3000 for power supply arrangements.
The in room indoor units are often powered from each tenants metered power supply (Check with AS3000).
Ownership of the apartment air conditioning system is by the apartment owner or tenant, including indoor unit and refrigeration pipework to on floor BC.
The apartment owner / occupier is required to enter into a negotiated energy supply and billing arrangement directly with the body corporate.
The system will come complete with a manufacturers BMCS system. This system will determine the power consumption of the refrigeration system for each apartment. The body corporate or the body corporate via an independent billing company will be required to retrieve costs from each tenant. Often a bond is required for this cost in case of non-payment or dispute.
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