Media · source heat · heat pump
Source heat: the lower, the better.
Buildings are better insulated every year and need less heat. Less heat means lower water temperature. And low water temperature is where a heat pump works most efficiently. The future lies where the source water drops almost to room temperature.
Chain of causation
Four links, one result.
The envelope improves
Walls, roofs and windows let less heat escape.
The heat load falls
Less heating power is needed per square metre.
The water cools
A large radiant surface gives the same comfort with low water temperature.
Efficiency rises
The heat pump moves more heat with less electricity.
Data evidence · 1970–2010
Source temperature has approached floor temperature.
In radiator systems, boiler water fell only from 90 °C to 70 °C in forty years. In underfloor heating (ISIYER), over the same period it fell from 60 °C to 30 °C: the water temperature became almost equal to the floor temperature.
- Radiator: small surface, high temperature required
- Underfloor heating: large surface, low temperature is enough
- The floor surface stays below the 29 °C comfort limit
Cross-check · the Carnot limit
Why low temperature? That is what physics says.
The theoretical maximum efficiency of a heat pump depends on how high it “pumps” the heat. The lower the target temperature, the more heat is moved with the same electricity.
| Flow water | System | Carnot COP | Realistic COP* |
|---|---|---|---|
| 70 °C | Old radiator | 4,9 | ≈ 2.2 |
| 55 °C | New radiator | 6,0 | ≈ 2.7 |
| 45 °C | Fan coil / low-temperature radiator | 7,1 | ≈ 3.2 |
| 35 °C | ISIYER · Bioiklim | 8,8 | ≈ 4.0 |
* Assuming outdoor air at 0 °C (273.15 K); real devices reach about 45% of the Carnot limit. Result: a heat pump running at 35 °C uses about 1.8 times less electricity for the same heat than one running at 70 °C.
The most important device · the heat pump
It does not produce heat, it moves it.
A heat pump collects heat from the outdoor air with a refrigerant, raises its temperature with a compressor and releases it into the floor. The electricity used is only part of the heat moved. In summer the same device reverses the cycle and moves the home’s heat outside.
Flow/return water; floor surface ≤ 29 °C
Flow/return water; a dew-point sensor prevents condensation
Dew-point control
A humidity sensor continuously measures the dew point in the room. The water temperature never drops below this value, so no condensation forms on the ceiling or floor.
Let’s build the future today.
Low-temperature radiant systems and heat pumps: let’s design them together for a new building or a conversion.