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Can a Heat pump replace a boiler?

(Press F5 if not auto start). Can a Heat pump replace a boiler?. (arrow-down or mouse-click). Not without a bit of thought. Maximum efficiencies are unlikely to be achieved without a few changes to the system. Let us consider a Condensing boiler circuit. Example. Heat output approximates

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Can a Heat pump replace a boiler?

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  1. (Press F5 if not auto start) Can a Heat pump replace a boiler? (arrow-down or mouse-click) Not without a bit of thought. Maximum efficiencies are unlikely to be achieved without a few changes to the system

  2. Let us consider a Condensing boiler circuit Example Heat output approximates to average (mean) flow-return temperature Flue losses 10 – 15% 85 – 90% energy to water 56°C 56°C (Flow-rate 1) 50°C rt = 12° Boiler 44°C 44°C http://www.heatpumps.co.uk/heatpumpcalculator.html Low return temperature helps condensing- increases efficiency

  3. Let’s replace the boiler with a heat pump

  4. Heat pumps are fundamentally different to boilers Example Heat output approximates to average (mean) flow-return temperature Keeping flow temperature low increases energy efficiency Same heat output As previous slide 53°C 53°C (Flow-rate x 2) 50°C rt = 6° Heat Pump 47°C 47°C Electrical input (relative to heat output) can vary considerably http://www.heatpumps.co.uk/heatpumpcalculator.html

  5. The ‘flow’ is now 3° colder, and the ‘return’ is 3° hotter, but the average temperature is unchanged. How did we achieve these temperature changes? In our example we have doubled the water flow rate. Remember, our heat (kW) is the same in every example. Note: - To increase the flow-rate, the pipe diameter is likely to have to be bigger so that pumping power is not increased. (pump energy is an energy loss).

  6. Heat pumps are fundamentally different to boilers Heat (kW) = Flow rate (lit/sec) x 4.2 x rt Heat output approximates to average (mean) flow-return temperature (Repeat of previous slide) Simple formula for heat, water flow and temperature difference Keeping flow temperature low increases energy efficiency Same heat output As previous slide Example 53°C 53°C (Flow-rate x 2) 50°C rt = 6° Heat Pump 47°C 47°C Electrical input (relative to heat output) can vary considerably http://www.heatpumps.co.uk/heatpumpcalculator.html

  7. You might think that the heat transfer is better when there is a large flow-return temperature difference. However, it all depends on how fast the heat is taken away. i.e. it depends in the water flow rate. If the heat transfer (kW) is constant, and the flow rate is doubled, then the temperature difference between the flow and return is halved. Our heat pump prefers this, it ‘sees’ a lower flow temperature.

  8. How can we reduce the working temperature further? Increase the size of the radiator. A bigger radiator will emit more heat, so the temperatures are ‘dragged down’ to a lower temperature.

  9. Now with a bigger radiator All temperatures now 12° lower. Rule of thumb: - 1° drop in water temperature can result in about 2.5% improvement in system efficiency. A bigger emitter system reduces the working temperatures. This increases the COP significantly. Keeping flow temperature low increases energy efficiency Same heat output but at lower temperature Example 41°C 41°C (Flow-rate x 2) 38°C rt = 6° Heat Pump 35°C 35°C (Doubling the radiator area can reduce the mean temperature from 50° to about 38°C) (see radiator manufacturer’s data)

  10. Could we have done anything else? If we insulate the house more, then less heat is needed, this can reduce the water temperatures required. This therefore increases the energy efficiency of the heat pump.

  11. What else could reduce the temperature?

  12. Now with underfloor heating Better still :- underfloor heating designed for low temperatures Keeping flow temperature low increases energy efficiency Example Pipes in floor screed 36°C 36°C (Flow-rate x 2) 43°C rt = 6° Heat Pump 30°C 30°C Note : - In general, tiles or slabs on screed give better results than wood. http://www.heatpumps.co.uk/heatpumpcalculator.html

  13. So, we now have an efficient heat pump system. It took a few changes But the increase in energy efficiency makes the long term energy savings worthwhile Don’t forget to check your heat pump’s settings. A simple adjustment to reduce the water temperature in the heating system will save energy.

  14. This last slide is simply a summary of the previous examples, showing approximate implications to the efficiency (COP) It should be noted that the above are mid-winter temperatures. With weather-compensation, the temperatures can be reduced at milder times, thus increasing the COP.

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