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What is the real story around heat pumps?

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pcprogrammer:
At the moment we are looking for a heat pump system to replace our wood burner. Asked three companies to come and give a quotation. The responses vary quite a bit.

The first one suggested that heat pumps and specifically air to water systems are no good for where we live. They would consume more energy due to colder winters up here. (~500m above sea level) His advice was to look into fuel or pellet burners. Would be cheaper to install and on par with what we now pay per year for fire wood.

Well guess again, his quotations for a fuel based system came out to be on par with a geothermal heat pump system, and the pellet based system even much higher, so no to those. Would also not solve my wife's problem with the smells.

The second one suggested more or less the same for air to water heat pumps, due to the usage of additional direct electrical heating on very cold days. Annual energy consumption would be more then twice of what a geothermal system would use.

The third one told us the opposite. Big fan of Mitsubishi Electric air to water heat pump. They would dimension it such that no additional direct electrical heating would be needed. They were also dismissive about the brand of heat pump offered by the second party. (De Dietrich) Did not receive their quotation yet, since they only came by yesterday.

The problem I found with comparing all the data is the way the coefficient of performance is specified. There are tables that show the relations between outside temperature and requested inside water temperature, but to make a more or less correct calculation on energy consumption is not easy to do. I do know how much energy our house uses based on the data collection from my computer controlled heating system.

The COP in the general data sheets is given mainly for 35 degree Celsius output water, and an input temperature that varies for the different systems. +7 and -7 for air to water systems and 0 for geothermal systems. (Based on glycol in the water)

Sure they give the seasonal COP, but again at 35 degree Celsius. On colder days how ever our house needs the water to be between 45 and 55 degree Celsius, which is possible, but at what expense.

So not an easy decision also given the fact that it is about a lot of money. (Between 15 - 40K euro)

Any thoughts on what to believe and how to make a better decision between an air to water and a geothermal system?

RoGeorge:
Heat pumps are advantageous when there is enough temperature difference, otherwise they'll become less efficient, or might not work at all.  If a company selling heat pumps advice against buying a heat pump, better listen to them.  Won't work.

Anyway, if you decide to replace the current wood burner, do not remove it, and keep a way to switch back to burning wood if necessary.  Heat pumps do not work without electricity, and electricity can not be stored, while a pile of wood is trivial to store indefinitely.

ebastler:
Here's an online calculator with data for many real-world heatpump units, which lets you select the water output temperature and plots efficiency as a function of building heat loss. It assumes British weather though, which -- depending on where you are -- may distort the calculations somewhat. (Since you mentioned 500m altitude, I assume that's not in the Netherlands?)

https://tools.bregroup.com/heatpumpefficiency/index.jsp

pcprogrammer:

--- Quote from: RoGeorge on February 17, 2024, 08:20:07 am ---Heat pumps are advantageous when there is enough temperature difference, otherwise they'll become less efficient, or might not work at all.  If a company selling heat pumps advice against buying a heat pump, better listen to them.  Won't work.

Anyway, if you decide to replace the current wood burner, do not remove it, and keep a way to switch back to burning wood if necessary.  Heat pumps do not work without electricity, and electricity can not be stored, while a pile of wood is trivial to store indefinitely.

--- End quote ---

Thanks for the input, but my central heating system as is also needs electricity to work  8)

The task of feeding the wood burner is daunting for me with my Fibromyalgia, and my wife hates the smell it gives. She loves to work outside in the garden and that becomes difficult on the days I have to burn the wood. In the colder periods it needs to burn every other day.

It is not that a heat pump would not work, it is a question about who is telling the "truth". Geothermal will work for sure, but is more expensive due to in our case the need for vertical loops. Drilling is expensive.

With geothermal the source is far more stable in temperature then when using air to water. But the COP goes down when you need 45 or 55 degrees Celsius of heating water to fulfill the need of the house. So both systems are less efficient when it is cold outside. Hence the seasonal COP being lower then the COP in ideal circumstances.

The question is how big the difference is in annual energy consumption between the two systems. Air to water and geothermal. I know it depends on a lot of factors, like the local climate, the size of the house, the insulation of the house, etc.

Another issue is the noise. We are very sensitive for it, and with the large fans in the external units the make more noise. There are a couple of installations in the village and when we walk by it bothers us. Not sure how it would be inside the house. The geothermal units are well insulated and produce not a lot of noise.

It is hard to make a well informed decision.

pcprogrammer:

--- Quote from: ebastler on February 17, 2024, 08:30:06 am ---Here's an online calculator with data for many real-world heatpump units, which lets you select the water output temperature and plots efficiency as a function of building heat loss. It assumes British weather though, which -- depending on where you are -- may distort the calculations somewhat. (Since you mentioned 500m altitude, I assume that's not in the Netherlands?)

https://tools.bregroup.com/heatpumpefficiency/index.jsp

--- End quote ---

Thanks.

Indeed we live in the middle of France.

Edit: We are Dutch though, that is why I use the Dutch flag. Not out of chauvinism, just to show that Dutch is my native language.  :)

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