A machine in every room.Or one water plant.
For condominiums, dormitories and staff housing. One plant in the basement carpark sends cold water and hot water to every room. No air-conditioner on the wall. No electric heater in the shower. Tenants pay the owner for cooling and hot water each month, and the building does not need a big transformer.
The same building, two ways.
A mid-rise residential building: 58 rooms on six floors, with a restaurant, a laundry and a convenience store on the ground floor. On the left, every room runs its own air-conditioner and its own shower heater. On the right, one plant in the basement carpark sends cold and hot water to every room and every shop.
58 compressors and 58 heaters in the rooms
Each one bought, wired, serviced and replaced on its own. A compressor hangs outside every room. The shops downstairs add their own.
One plant bay, one fan coil per room
Nothing on the outside walls. Nothing electric in the bathrooms. The roof deck stays clear.
A worked example of a typical mid-rise building. Pipe routes are fixed for each project at design stage.
What the owner gains
The plant belongs to the building. So does what it earns.
The monthly income comes to you
Each tenant pays you one monthly charge for cooling and hot water. They no longer pay the power company to run their own air-conditioner and shower heater. You run one plant and keep the difference, every month.
No big transformer
A shower heater and a compressor in every room all pull power at the same hour. That peak sets the size of the transformer and the wiring. One central plant draws far less, so the building does not need a big transformer.
The shops run on it too
The restaurant, the laundry and the convenience store on the ground floor take cooling and hot water from the same plant. They pay you the same way.
How the pipework runs through the building
The plant sits in the basement carpark. The pipes rise beside the lift lobby. A main runs along every corridor ceiling. Each room has one fan coil. Only water enters the rooms.
- Chilled water, flow and return
- Hot water, 45 °C
- Solar cable
Solar on the canopy roof
Panels on the roof canopy help run the plant by day. The cable runs down the core to the inverter. The building uses the power itself; none is exported.
Corridor main, every floor
Chilled water flow and return, plus one hot pipe, in the corridor ceiling from the 2nd to the 7th floor. PPR pipe, with a shut-off valve for each room.
One fan coil per room
A quiet fan and a water coil above the door, inside the room. It replaces the window air-conditioner.
Hot water to every shower
A short drop from the corridor main to each bathroom. No electric shower heater.
Inverter in the electrical room
The solar inverter and switchgear sit in the existing lower-ground electrical room, next to the generator.
Nothing on the outside walls
No condensers, no brackets, no drain lines. The building looks the way the architect drew it.
Risers beside the lift lobby
Two chilled pipes and one hot pipe climb from the basement ceiling to the 7th floor in one shaft. Same spot on every floor.
Plant bay in the basement carpark
Four heat pumps for chilled water, one for hot water, and a 3,000-litre tank. Two parking bays at the rear wall, ventilated to outside air through a louvre.
Shops on the ground floor
The restaurant, the laundry and the convenience store hang off the same riser. Chilled water to their fan coils, hot water to the kitchen and the wash.
A typical floor: the pipe route in plan
Twelve rooms a floor, six each side of the corridor. One pipe main runs along the corridor ceiling. Each room takes a short branch to its fan coil and its shower.
- Chilled water, flow and return
- Hot water, 45 °C
Swipe sideways to follow the corridor.
- Corridor mainChilled water flow and return, plus one hot-water pipe, run the full length of the corridor in the ceiling, both ways from the riser.
- Branch per roomA short pair of pipes turns into each room and ends at the fan coil above the door.
- Hot waterOne hot pipe drops to the shower in each bathroom, which sits on the corridor wall.
- RiserIn the corridor beside the lift lobby, straight up from the basement plant. Same spot on every floor.
The 6th and 7th floors have larger units. Same arrangement: one fan coil and one hot-water drop per unit. Pipe positions are sized and fixed for each project at design stage.
Why water, not refrigerant
A refrigerant system also clears the outside walls. The difference is what runs through the ceilings: gas in copper, or water in plastic pipe. What runs through the building decides what you maintain for the life of it.
- Refrigerant, gas and liquid lines
- Chilled water, flow and return
- Hot water, 45 °C
Refrigerant in every corridor and every room
High-pressure gas in long copper runs, with a joint at every branch. A leak is unseen until the cooling fades. Hot water needs its own system.
Water in the pipes, refrigerant in the plant
Plastic water pipe to every room. A leak is a drip you can see. Hot water comes from the same plant.
Three ways to cool the rooms and heat the showers
| Question | Window units + electric showers | Refrigerant system (VRF) | Karnot water system |
|---|---|---|---|
| What runs through the building | Nothing. Every room is its own machine. | Refrigerant gas at high pressure, in long copper runs through ceilings and rooms. | Water, in PPR pipe. The refrigerant stays sealed inside the plant. |
| Machines to look after | 116: a compressor and a shower heater in every room. | Outdoor units, 58 branded indoor units, and a separate hot-water system. | 5 heat pumps in one place. A fan and a coil in each room. |
| When something leaks | One room goes warm until the unit is replaced. | Gas escapes unseen. The circuit loses cooling until a specialist finds the leak and recharges it. | A drip you can see. Close that room's valve, fix it, reopen. |
| Hot water | An electric heater in every shower. Together they set the size of the transformer. | Not included. | Included, from the same plant. |
| Who can service it | Anyone, but 58 times over. | The brand's own technicians, parts and controls. | Any competent pipefitter for the pipework. Karnot for the plant. |
| Refrigerant | R32 or R410A inside every room. | R32 or R410A, carried through the occupied floors. | R290, a natural refrigerant, in the plant only. |
| Outside walls and noise | A compressor under every window. | Clear outside walls. Condensers on the roof. | Clear outside walls. Quiet rooms. |
| Where it wins | Lowest cost to buy. | Familiar to most contractors. No water in the ceilings. | One plant to run and maintain. The owner bills cooling and hot water as one monthly charge. |
A fair comparison: each option's strongest point is on the last row.
Questions we get asked
What is a central water plant?
One group of heat pumps in a single plant bay makes chilled water for cooling and hot water for showers. Pipes carry the water to every room. Each room has a fan coil, which is a quiet fan blowing over a water coil, in place of its own air-conditioner.
Where does the plant go, and how much space does it take?
In the worked example it takes two parking bays at the rear wall of the basement carpark: five heat pumps and a 3,000-litre hot-water tank. The bay is ventilated to outside air through a louvre. The position is fixed for each building at design stage.
Who do the tenants pay?
The building owner. Each tenant pays one monthly charge for cooling and hot water. The owner runs one plant and pays the power for it.
Does the building need a big transformer?
No. There is no electric shower heater and no compressor in each room, so the peak load is far lower. The central plant is the main load.
What happens if a pipe leaks?
A water leak shows itself: you see a drip. Close that room's valve, fix the pipe and reopen the valve. The rest of the building carries on.
Does each room still need an electric shower heater?
No. Hot water at 45 °C comes from the same plant. A short pipe drops from the corridor main to each bathroom.
Where is the refrigerant?
Sealed inside the heat pumps in the plant bay. It is R290, a natural refrigerant. Only water goes to the rooms. The plant bay is ventilated to outside air and has gas detection.
Who can service it?
Any competent pipefitter can work on the pipework. Karnot looks after the plant. There are five heat pumps in one place, not a machine in every room.
Planning a condominium or dormitory?
Send us a typical floor plan and the number of rooms. We draw your building this way and size the plant to it.