Hot water recovered from building cooling
How a 150-bed hospital can use water-source heat pumps on its chilled-water return to make all its 60–70 °C hot water while helping cool the building, and what it saves against a diesel-fired hot water boiler.
▶Video: Heating and cooling from one machine
V11 · 2–2.5 minWater-source heat pumps that chill and heat at the same time
Video coming soon01Problem statement
- Heat rejected and heat bought. The chillers reject building heat to cooling towers while the boiler burns diesel to heat water in the next room.
- Cooling runs all year. Hospitals need cooling day and night in most of India, so there is a steady supply of heat to recover.
- Hot water around the clock. Wards, kitchen and laundry use hot water at all hours, with peaks in the morning.
- Losses between fuel and process. Burning diesel in a boiler or heater and distributing the heat loses a quarter or more of the fuel's energy before it reaches the process.
- Compliance, safety and handling. Fired equipment brings boiler inspections, fuel storage and unloading, flue emissions and an attendant on every shift.
02Use case
The reference building is a 150-bed hospital with a chilled-water system serving fan coils and AHUs at 7/12 °C all year. It uses hot water for wards, kitchen and laundry, made in a diesel boiler.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Wards and patient rooms | 25 → 60 °C | 15,000 L/day, 25 → 60 °C | 610 |
| Kitchen | 25 → 60 °C | 3,000 L/day, 25 → 60 °C | 122 |
| Laundry | 25 → 60 °C | 400 kg linen × 12.5 L/kg, 25 → 60 °C; the washers’ own heaters add the last 10 K | 203 |
| Storage and pipework standing losses | – | about 5% | 47 |
| Total useful heat | 981 | ||
Averaged over 18 running hours, the heat pumps need about 55 kW.
03P&ID
Tags: HP heat pump, TK tank, SG steam generator, P pump, PHE plate heat exchanger, TCV temperature control valve, TIC temperature indicating controller (panel), TT temperature transmitter, MT moisture transmitter, PT pressure transmitter, LT level transmitter, FS flow switch, NC normally closed. Process fluids are heated through their own exchanger, coil or jacket.
04Solution
System description
- 1 × SE-WW-55V (55 kW) (SE-WW water-source heat pump) delivering 60 °C, covering the day's 981 kWh in about 17.8 running hours.
- A 2,000 L insulated storage tank decouples the heat pumps from the process peaks.
- Heat source: fan-coil chilled-water return at about 12 °C. The heat pump evaporators chill fan-coil water from 12 °C to 7 °C, taking load off the existing chillers.
- The diesel-fired hot water boiler stays connected behind a normally closed valve as standby.
- The heat pumps take a side stream of the 12 °C chilled-water return and send it back to the chilled-water supply header at 7 °C, so their evaporators do part of the building's cooling.
- Their condensers make 65–70 °C water into insulated storage tanks for wards, kitchen and laundry.
- The existing chillers continue to carry the rest of the cooling load and run less as the heat pumps take their share.
- The heat pumps are sized on hot water demand, so every kWh of their heat is used.
Selected equipment
| Model | SE-WW-55V × 1 |
|---|---|
| Heating capacity | 55 kW each, 55 kW total |
| COP | 4.7 at the data sheet's rated condition (55 °C outlet) |
| Power input | about 11.6 kW total at rated conditions |
| Rating | hot and chilled water at the same time, to 60 °C |
| Supply temperature | 60 °C |
| Storage | 2,000 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the top of the tank starts the heat pumps below 62 °C and stops them at 68 °C. A temperature sensor on the chilled-water side stream keeps the evaporator leaving water at 7 °C and stops the heat pumps if chilled-water flow is lost. The chillers' own controls handle the remaining cooling load, and the diesel boiler stays as standby for hot water.
05Energy saving and ROI
Change any input to match a customer's site. Defaults are typical Indian prices for October 2026. The installed cost is a placeholder; replace it with the actual quotation.
| Existing | Heat pump | |
|---|---|---|
| Daily consumption | – | – |
| Annual energy cost | – | – |
| Cost per occupied bed | – | – |
| CO₂ per year | – | – |
06Benefits
Hot water from cooling heat
Heat already removed from the building becomes hot water instead of going to the cooling tower.
Chillers work less
Every kWh of hot water comes with about 0.7 kWh of chilled water, which reduces chiller running hours.
Less cooling tower water
Heat taken by the heat pumps is not rejected at the towers, saving make-up water.
Lower energy cost
Each kWh of electricity delivers about 4.7 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
No flame on site
No burner, flue or fuel tank for this duty, and no fuel deliveries to schedule.
Solar-ready
Running hours can be placed in daylight so rooftop solar supplies much of the electricity, which also cuts CO₂ further.
07Engineering pointers
Site data to collect
- Chiller capacity and chilled-water flow and temperatures
- Hourly cooling load profile
- Daily hot water use for wards, kitchen and laundry
- Current boiler fuel use
- Plant room space near the chilled-water header
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
Design notes
- Hydraulics. Connect the heat pumps in parallel with the chillers on a decoupled header so their flow does not upset chiller flow or control.
- Legionella. Store hot water at 60 °C, keep circulation returns above 50 °C and run a weekly high-temperature cycle.
- Cooling only when needed. If cooling demand falls, the heat pumps must stop or switch to an air or tower source. Check winter cooling load before sizing.
- Electrical. About 12 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Source stream. The source must give up roughly two-thirds of the heat delivered. Confirm its flow and temperature over a full production day, and filter it before the evaporator.
- Water quality. Scale forms quickly above 60 °C. Use softened make-up and keep the heat pump loop closed, with process fluids on the far side of an exchanger or coil.
Service and warranty
Sunniva has supplied 5,000+ heat pumps since 2012, with nine service technicians across India, including remote sites such as Leh. All components carry a one-year warranty.
Talk to us
Hot water recovered from building cooling
How a 150-bed hospital can use water-source heat pumps on its chilled-water return to make all its 60–70 °C hot water while helping cool the building, and what it saves against a diesel-fired hot water boiler.
▶Video: Heating and cooling from one machine
V11 · 2–2.5 minWater-source heat pumps that chill and heat at the same time
Video coming soon01Problem statement
- Heat rejected and heat bought. The chillers reject building heat to cooling towers while the boiler burns diesel to heat water in the next room.
- Cooling runs all year. Hospitals need cooling day and night in most of India, so there is a steady supply of heat to recover.
- Hot water around the clock. Wards, kitchen and laundry use hot water at all hours, with peaks in the morning.
- Losses between fuel and process. Burning diesel in a boiler or heater and distributing the heat loses a quarter or more of the fuel's energy before it reaches the process.
- Compliance, safety and handling. Fired equipment brings boiler inspections, fuel storage and unloading, flue emissions and an attendant on every shift.
02Use case
The reference building is a 150-bed hospital with a chilled-water system serving fan coils and AHUs at 7/12 °C all year. It uses hot water for wards, kitchen and laundry, made in a diesel boiler.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Wards and patient rooms | 25 → 60 °C | 15,000 L/day, 25 → 60 °C | 610 |
| Kitchen | 25 → 60 °C | 3,000 L/day, 25 → 60 °C | 122 |
| Laundry | 25 → 60 °C | 400 kg linen × 12.5 L/kg, 25 → 60 °C; the washers’ own heaters add the last 10 K | 203 |
| Storage and pipework standing losses | – | about 5% | 47 |
| Total useful heat | 981 | ||
Averaged over 18 running hours, the heat pumps need about 55 kW.
03P&ID
Tags: HP heat pump, TK tank, SG steam generator, P pump, PHE plate heat exchanger, TCV temperature control valve, TIC temperature indicating controller (panel), TT temperature transmitter, MT moisture transmitter, PT pressure transmitter, LT level transmitter, FS flow switch, NC normally closed. Process fluids are heated through their own exchanger, coil or jacket.
04Solution
System description
- 1 × SE-WW-55V (55 kW) (SE-WW water-source heat pump) delivering 60 °C, covering the day's 981 kWh in about 17.8 running hours.
- A 2,000 L insulated storage tank decouples the heat pumps from the process peaks.
- Heat source: fan-coil chilled-water return at about 12 °C. The heat pump evaporators chill fan-coil water from 12 °C to 7 °C, taking load off the existing chillers.
- The diesel-fired hot water boiler stays connected behind a normally closed valve as standby.
- The heat pumps take a side stream of the 12 °C chilled-water return and send it back to the chilled-water supply header at 7 °C, so their evaporators do part of the building's cooling.
- Their condensers make 65–70 °C water into insulated storage tanks for wards, kitchen and laundry.
- The existing chillers continue to carry the rest of the cooling load and run less as the heat pumps take their share.
- The heat pumps are sized on hot water demand, so every kWh of their heat is used.
Selected equipment
| Model | SE-WW-55V × 1 |
|---|---|
| Heating capacity | 55 kW each, 55 kW total |
| COP | 4.7 at the data sheet's rated condition (55 °C outlet) |
| Power input | about 11.6 kW total at rated conditions |
| Rating | hot and chilled water at the same time, to 60 °C |
| Supply temperature | 60 °C |
| Storage | 2,000 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the top of the tank starts the heat pumps below 62 °C and stops them at 68 °C. A temperature sensor on the chilled-water side stream keeps the evaporator leaving water at 7 °C and stops the heat pumps if chilled-water flow is lost. The chillers' own controls handle the remaining cooling load, and the diesel boiler stays as standby for hot water.
05Energy saving and ROI
Change any input to match a customer's site. Defaults are typical Indian prices for October 2026. The installed cost is a placeholder; replace it with the actual quotation.
| Existing | Heat pump | |
|---|---|---|
| Daily consumption | – | – |
| Annual energy cost | – | – |
| Cost per occupied bed | – | – |
| CO₂ per year | – | – |
06Benefits
Hot water from cooling heat
Heat already removed from the building becomes hot water instead of going to the cooling tower.
Chillers work less
Every kWh of hot water comes with about 0.7 kWh of chilled water, which reduces chiller running hours.
Less cooling tower water
Heat taken by the heat pumps is not rejected at the towers, saving make-up water.
Lower energy cost
Each kWh of electricity delivers about 4.7 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
No flame on site
No burner, flue or fuel tank for this duty, and no fuel deliveries to schedule.
Solar-ready
Running hours can be placed in daylight so rooftop solar supplies much of the electricity, which also cuts CO₂ further.
07Engineering pointers
Site data to collect
- Chiller capacity and chilled-water flow and temperatures
- Hourly cooling load profile
- Daily hot water use for wards, kitchen and laundry
- Current boiler fuel use
- Plant room space near the chilled-water header
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
Design notes
- Hydraulics. Connect the heat pumps in parallel with the chillers on a decoupled header so their flow does not upset chiller flow or control.
- Legionella. Store hot water at 60 °C, keep circulation returns above 50 °C and run a weekly high-temperature cycle.
- Cooling only when needed. If cooling demand falls, the heat pumps must stop or switch to an air or tower source. Check winter cooling load before sizing.
- Electrical. About 12 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Source stream. The source must give up roughly two-thirds of the heat delivered. Confirm its flow and temperature over a full production day, and filter it before the evaporator.
- Water quality. Scale forms quickly above 60 °C. Use softened make-up and keep the heat pump loop closed, with process fluids on the far side of an exchanger or coil.
Service and warranty
Sunniva has supplied 5,000+ heat pumps since 2012, with nine service technicians across India, including remote sites such as Leh. All components carry a one-year warranty.