Precast concrete curing with hot water
How a precast plant casting 40 m³ of concrete a day can accelerate curing with heat-pump hot water, and what it saves against a biomass briquette-fired steam boiler.
▶Video: Hot air from heat pump hot water
V05 · 2–2.5 minAir coils for spray dryers, stenters, kilns, paint booths and ovens
Video coming soon01Problem statement
- Live steam is hard to control. Steam lances overheat elements near the outlet and leave far corners cool, which gives uneven strength and surface cracks.
- Boiler needs fuel handling and attendants. Briquette boilers need daily fuel handling, ash removal and a certified attendant.
- Mould turnaround drives output. Plant output depends on reaching demoulding strength overnight, so curing must be reliable every day.
- Losses between fuel and process. Burning briquettes 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 casts hollow-core slabs, wall panels and drains. It pours about 40 m³ of concrete a day into steel moulds in eight curing chambers and on heated casting beds, demoulding the next morning.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Heating fresh concrete | 25 → 55 °C | 40 m³ × 2,400 kg/m³ × 0.88 kJ/kg·K × 30 K | 704 |
| Heating steel moulds | 25 → 55 °C | 40 t steel × 0.46 kJ/kg·K × 30 K | 153 |
| Chamber and bed losses | 55–60 °C | 8 chambers × 3 kW × 12 h | 288 |
| Storage and pipework standing losses | – | about 5% | 57 |
| Total useful heat | 1,202 | ||
Averaged over 20 running hours, the heat pumps need about 60 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
- 4 × SE-SHT-16C (64 kW total) (SE-SHT cascade heat pump) delivering 75 °C, covering the day's 1,202 kWh in about 18.8 running hours.
- A 2,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The briquette-fired steam boiler stays connected behind a normally closed valve as standby.
- Finned pipe coils with circulation fans heat each curing chamber, and pipes under the steel casting beds heat the long-line beds.
- Each chamber follows its own curing profile: a preset period, a controlled ramp of no more than 20 K/h, a hold at 55–60 °C and a slow cool-down.
- The storage tank is charged during the day so the night curing load is met without the boiler.
Selected equipment
| Model | SE-SHT-16C × 4 |
|---|---|
| Heating capacity | 16 kW each, 64 kW total |
| COP | 2.7 at A20 °C / W90 °C (data sheet T1) |
| Power input | about 23.8 kW total at rated conditions |
| Rating | cascade R410A + R515B, rated 90 °C, 95 °C maximum |
| Supply temperature | 75 °C |
| Storage | 2,000 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pumps below 70 °C and stops them at 75 °C. TIC-201 on each chamber ramps the coil valve to follow the curing profile. TIC-202 holds the casting beds at 55 °C. The boiler is retained on standby for cold-weather peaks.
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 m³ of concrete | – | – |
| CO₂ per year | – | – |
06Benefits
More even strength
Hot-water coils and beds heat uniformly, reducing cold corners, hot spots and thermal cracking.
Programmable curing cycles
Each chamber follows a set ramp and hold, which is hard to achieve with manual steam valves.
No fuel yard
No daily briquette handling, ash disposal or boiler attendant for the curing load.
Lower energy cost
Each kWh of electricity delivers about 2.7 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.
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
- Concrete volume poured per day
- Number and size of curing chambers and beds
- Mould weight and demoulding time
- Current curing profile and briquette use
- 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
- Keep the concrete moist. Steam adds moisture and hot water does not. Cover elements or add a water tray or fog nozzle in each chamber so surfaces do not dry out.
- Respect ramp limits. Follow the preset period and a ramp rate of 20 K/h or less to avoid delayed ettringite and microcracking.
- Electrical. About 24 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
Precast concrete curing with hot water
How a precast plant casting 40 m³ of concrete a day can accelerate curing with heat-pump hot water, and what it saves against a biomass briquette-fired steam boiler.
▶Video: Hot air from heat pump hot water
V05 · 2–2.5 minAir coils for spray dryers, stenters, kilns, paint booths and ovens
Video coming soon01Problem statement
- Live steam is hard to control. Steam lances overheat elements near the outlet and leave far corners cool, which gives uneven strength and surface cracks.
- Boiler needs fuel handling and attendants. Briquette boilers need daily fuel handling, ash removal and a certified attendant.
- Mould turnaround drives output. Plant output depends on reaching demoulding strength overnight, so curing must be reliable every day.
- Losses between fuel and process. Burning briquettes 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 casts hollow-core slabs, wall panels and drains. It pours about 40 m³ of concrete a day into steel moulds in eight curing chambers and on heated casting beds, demoulding the next morning.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Heating fresh concrete | 25 → 55 °C | 40 m³ × 2,400 kg/m³ × 0.88 kJ/kg·K × 30 K | 704 |
| Heating steel moulds | 25 → 55 °C | 40 t steel × 0.46 kJ/kg·K × 30 K | 153 |
| Chamber and bed losses | 55–60 °C | 8 chambers × 3 kW × 12 h | 288 |
| Storage and pipework standing losses | – | about 5% | 57 |
| Total useful heat | 1,202 | ||
Averaged over 20 running hours, the heat pumps need about 60 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
- 4 × SE-SHT-16C (64 kW total) (SE-SHT cascade heat pump) delivering 75 °C, covering the day's 1,202 kWh in about 18.8 running hours.
- A 2,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The briquette-fired steam boiler stays connected behind a normally closed valve as standby.
- Finned pipe coils with circulation fans heat each curing chamber, and pipes under the steel casting beds heat the long-line beds.
- Each chamber follows its own curing profile: a preset period, a controlled ramp of no more than 20 K/h, a hold at 55–60 °C and a slow cool-down.
- The storage tank is charged during the day so the night curing load is met without the boiler.
Selected equipment
| Model | SE-SHT-16C × 4 |
|---|---|
| Heating capacity | 16 kW each, 64 kW total |
| COP | 2.7 at A20 °C / W90 °C (data sheet T1) |
| Power input | about 23.8 kW total at rated conditions |
| Rating | cascade R410A + R515B, rated 90 °C, 95 °C maximum |
| Supply temperature | 75 °C |
| Storage | 2,000 L insulated tank |
Ratings from the Sunniva TDS 2026 data sheets.
Control philosophy
TT-101 at the tank top starts the heat pumps below 70 °C and stops them at 75 °C. TIC-201 on each chamber ramps the coil valve to follow the curing profile. TIC-202 holds the casting beds at 55 °C. The boiler is retained on standby for cold-weather peaks.
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 m³ of concrete | – | – |
| CO₂ per year | – | – |
06Benefits
More even strength
Hot-water coils and beds heat uniformly, reducing cold corners, hot spots and thermal cracking.
Programmable curing cycles
Each chamber follows a set ramp and hold, which is hard to achieve with manual steam valves.
No fuel yard
No daily briquette handling, ash disposal or boiler attendant for the curing load.
Lower energy cost
Each kWh of electricity delivers about 2.7 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.
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
- Concrete volume poured per day
- Number and size of curing chambers and beds
- Mould weight and demoulding time
- Current curing profile and briquette use
- 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
- Keep the concrete moist. Steam adds moisture and hot water does not. Cover elements or add a water tray or fog nozzle in each chamber so surfaces do not dry out.
- Respect ramp limits. Follow the preset period and a ramp rate of 20 K/h or less to avoid delayed ettringite and microcracking.
- Electrical. About 24 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.