Boiler make-up water preheated by heat pumps
How a plant with a 5 tonne-per-hour steam boiler and poor condensate return can preheat make-up water to 85 °C with heat pumps, and what it saves against firing the furnace-oil boiler for that heat.
▶Video: Process heat for engineering and utilities
V06 · 2–2.5 minPlating, phosphating, washers, curing and boiler feedwater
Video coming soon01Problem statement
- Cold make-up costs fuel. Every litre of make-up water heated from 30 °C inside the boiler uses expensive furnace oil.
- Cold feed tank holds oxygen. A feed tank below 80 °C holds more dissolved oxygen, which causes pitting in the boiler and feed lines.
- Live steam heating wastes steam. Plants often heat the feed tank with live steam, which uses boiler output that could go to process.
- Losses between fuel and process. Burning furnace oil 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 plant runs a 5 tonne-per-hour furnace-oil steam boiler for about 20 hours a day. Only 60% of condensate returns, so about 2 m³ of cold make-up water enters the feed tank every hour.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Make-up water preheat | 30 → 85 °C | 2 m³/h × 20 h = 40,000 L/day, 30 → 85 °C | 2,554 |
| Feed tank top-up heating | 60 → 85 °C | 10,000 L/day returned condensate and mixed feed, 60 → 85 °C | 290 |
| Storage and pipework standing losses | – | about 5% | 142 |
| Total useful heat | 2,987 | ||
Averaged over 20 running hours, the heat pumps need about 149 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
- 3 × SE-SHT-50C (150 kW total) (SE-SHT cascade heat pump) delivering 95 °C, covering the day's 2,987 kWh in about 19.9 running hours.
- A 4,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The furnace-oil fired steam boiler stays connected behind a normally closed valve as standby.
- Softened make-up water passes through a plate exchanger heated with 95 °C water before entering the feed tank.
- A coil in the feed tank holds it at 85 °C, replacing live steam sparging.
- The boiler's own steam sparge stays in place as standby.
Selected equipment
| Model | SE-SHT-50C × 3 |
|---|---|
| Heating capacity | 50 kW each, 150 kW total |
| COP | 2.6 at A20 °C / W90 °C (data sheet T1) |
| Power input | about 55.8 kW total at rated conditions |
| Rating | cascade R410A + R515B, rated 90 °C, 95 °C maximum |
| Supply temperature | 95 °C |
| Storage | 4,500 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pumps below 90 °C and stops them at 95 °C. TIC-201 holds make-up water leaving PHE-201 at 85 °C. TIC-202 holds the feed tank at 85 °C and opens the steam sparge valve only if the tank falls below 80 °C.
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 tonne of steam | – | – |
| CO₂ per year | – | – |
06Benefits
Direct fuel saving
Each degree of feed temperature the heat pump supplies is heat the boiler no longer burns oil for.
Less dissolved oxygen
A hot feed tank holds less oxygen, which reduces corrosion and oxygen scavenger dosing.
More steam for process
Steam once used to heat the feed tank goes to production instead.
Lower energy cost
Each kWh of electricity delivers about 2.6 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.
Built-in redundancy
Several machines share the load. If one is serviced, the others and the storage carry most of the day, with the existing heater in reserve.
07Engineering pointers
Site data to collect
- Boiler capacity, pressure and running hours
- Condensate return percentage and temperature
- Make-up water flow and feed tank temperature
- Monthly furnace oil consumption
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
- Winter minimum ambient at site
Design notes
- Feed pump NPSH. Hotter feedwater reduces NPSH available. Check the feed pump suction head and tank elevation before raising feed temperature.
- Economiser. If the boiler has an economiser, hotter feedwater raises stack temperature. Check acid dew point and the overall saving.
- Use softened water. Preheat after the softener only, so the exchanger does not scale.
- Electrical. About 56 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Winter output. The SE-SHT cascade gives about 80% of rated output at 7 °C ambient and still runs at −20 °C. Size on the coldest design day for northern sites.
- 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
Boiler make-up water preheated by heat pumps
How a plant with a 5 tonne-per-hour steam boiler and poor condensate return can preheat make-up water to 85 °C with heat pumps, and what it saves against firing the furnace-oil boiler for that heat.
▶Video: Process heat for engineering and utilities
V06 · 2–2.5 minPlating, phosphating, washers, curing and boiler feedwater
Video coming soon01Problem statement
- Cold make-up costs fuel. Every litre of make-up water heated from 30 °C inside the boiler uses expensive furnace oil.
- Cold feed tank holds oxygen. A feed tank below 80 °C holds more dissolved oxygen, which causes pitting in the boiler and feed lines.
- Live steam heating wastes steam. Plants often heat the feed tank with live steam, which uses boiler output that could go to process.
- Losses between fuel and process. Burning furnace oil 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 plant runs a 5 tonne-per-hour furnace-oil steam boiler for about 20 hours a day. Only 60% of condensate returns, so about 2 m³ of cold make-up water enters the feed tank every hour.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Make-up water preheat | 30 → 85 °C | 2 m³/h × 20 h = 40,000 L/day, 30 → 85 °C | 2,554 |
| Feed tank top-up heating | 60 → 85 °C | 10,000 L/day returned condensate and mixed feed, 60 → 85 °C | 290 |
| Storage and pipework standing losses | – | about 5% | 142 |
| Total useful heat | 2,987 | ||
Averaged over 20 running hours, the heat pumps need about 149 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
- 3 × SE-SHT-50C (150 kW total) (SE-SHT cascade heat pump) delivering 95 °C, covering the day's 2,987 kWh in about 19.9 running hours.
- A 4,500 L insulated storage tank decouples the heat pumps from the process peaks.
- The furnace-oil fired steam boiler stays connected behind a normally closed valve as standby.
- Softened make-up water passes through a plate exchanger heated with 95 °C water before entering the feed tank.
- A coil in the feed tank holds it at 85 °C, replacing live steam sparging.
- The boiler's own steam sparge stays in place as standby.
Selected equipment
| Model | SE-SHT-50C × 3 |
|---|---|
| Heating capacity | 50 kW each, 150 kW total |
| COP | 2.6 at A20 °C / W90 °C (data sheet T1) |
| Power input | about 55.8 kW total at rated conditions |
| Rating | cascade R410A + R515B, rated 90 °C, 95 °C maximum |
| Supply temperature | 95 °C |
| Storage | 4,500 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pumps below 90 °C and stops them at 95 °C. TIC-201 holds make-up water leaving PHE-201 at 85 °C. TIC-202 holds the feed tank at 85 °C and opens the steam sparge valve only if the tank falls below 80 °C.
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 tonne of steam | – | – |
| CO₂ per year | – | – |
06Benefits
Direct fuel saving
Each degree of feed temperature the heat pump supplies is heat the boiler no longer burns oil for.
Less dissolved oxygen
A hot feed tank holds less oxygen, which reduces corrosion and oxygen scavenger dosing.
More steam for process
Steam once used to heat the feed tank goes to production instead.
Lower energy cost
Each kWh of electricity delivers about 2.6 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.
Built-in redundancy
Several machines share the load. If one is serviced, the others and the storage carry most of the day, with the existing heater in reserve.
07Engineering pointers
Site data to collect
- Boiler capacity, pressure and running hours
- Condensate return percentage and temperature
- Make-up water flow and feed tank temperature
- Monthly furnace oil consumption
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
- Winter minimum ambient at site
Design notes
- Feed pump NPSH. Hotter feedwater reduces NPSH available. Check the feed pump suction head and tank elevation before raising feed temperature.
- Economiser. If the boiler has an economiser, hotter feedwater raises stack temperature. Check acid dew point and the overall saving.
- Use softened water. Preheat after the softener only, so the exchanger does not scale.
- Electrical. About 56 kW of heat pump input at rated conditions, plus pumps and fans. Check spare sanctioned load before ordering.
- Winter output. The SE-SHT cascade gives about 80% of rated output at 7 °C ambient and still runs at −20 °C. Size on the coldest design day for northern sites.
- 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.