# Can a Heat pump replace a boiler? Not without a bit of thought. Maximum efficiencies are unlikely to be achieved without a few changes to the system (Press.

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

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

Lets replace the boiler with a heat pump

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

How did we achieve these temperature changes? 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). Remember, our heat (kW) is the same in every example. In our example we have doubled the water flow rate. The flow is now 3° colder, and the return is 3° hotter, but the average temperature is unchanged.

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

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. 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.

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.

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

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.

What else could reduce the temperature?

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

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 Dont forget to check your heat pumps settings. A simple adjustment to reduce the water temperature in the heating system will save energy.

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. This last slide is simply a summary of the previous examples, showing approximate implications to the efficiency (COP)

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