Living with an air source heat pump
Posted by Cathy Debenham on 24 January 2012 at 7:54 pm
I regularly write about air source heat pumps, but until recently my knowledge was only academic, but on a recent trip to New Zealand I discovered what they are actually like to live with.
At least three of the houses we stayed in were heated by an air to air heat pump. This means that the heat pump blows warm air into the room/house - and can be used in summer for air conditioning (cooling).
There have been two different approaches: the most common is to have a unit mounted on the wall of the main living room. It looks like the sort of air conditioning unit that I've often seen in offices in the UK, but never (so far) in anyone's home (see picture).
Like the air conditioning in a car, this is programmed to a certain temperature, and it blows hot air (or cold in summer) out into the room. Like a car, it's both rather noisy, when it's going (which isn't all the time), and a bit drafty if you're sitting in the line of fire. It's also makes the air in the room quite dry.
In the UK, domestic air source heat pump installations are more likely to be air to water. This means that the pump heats water, that is then circulated round underfloor heating or radiators to heat the house. This means there isn't noise or a draft.
The unit that does the work is on the outside of the house, and I didn't notice any discernable noise from it when we were inside. However, I know the owners of the house had a serious problem with noise when their nearest neighbours put three units on their external wall, about 4m away. What I did notice was a huge blast of cold air as I walked past it. I guess it would be belching out hot air in summer.
Home heating in New Zealand is totally different from the UK. They make most of our homes seem lovely and warm. Virtually no one has central heating. In most cases the focus is on heating the main living room - usually with a heat pump or a wood burning stove.
Elsewhere there's probably a heated towel rail and a small blow heater in the bathroom and electric blankets in all the beds, plus various electric heaters around the house.
It has taken the Kiwis a long time to get round to the idea that insulation is a good thing. It's only in the past 10 years or so that it's been compulsory to insulate new homes and to double glaze them. Most of the places we stayed in didn't appear to have either.
We did stay in one very new house with central heating. It is powered by an air source heat pump, and has solar thermal panels on the roof to heat the hot water. It has vents, either in the floor or walls, where warm air is blown in. I didn't notice the drafts so much, or that it dried the atmosphere, but the noise was worse. While I didn't necessarily notice when it fired up, it was always a relief when it stopped and we noticed how quiet it was.
I wasn't paying the electricity bill in any of these places, so can't tell you how economic or otherwise the heat pumps are. However, where they have replaced electric heaters, it's likely that they have led to significant savings.
The jury is out for the people who have replaced old wood burners that didn't meet the new Kiwi emissions standards. Most of the people I talked to seemed a bit disgruntled (and cold) because heating the living room to the same temperature cost significantly more with an ASHP than it had with a woodburner (timber is one of New Zealand's biggest industries, and wood has historically been cheap).
Electricity has also traditionally been cheap and plentiful in New Zealand, where the grid is powered by 80% renewable sources thanks to lots of hydro and geothermal generation. However, with increasing demand, and political difficulty damming more valleys, prices are likely to rise, and the percentage of grid electricity that's renewable has fallen.
We came back thinking how lucky we are to live in a well insulated, centrally heated house, but also with pause for thought. An American family visiting NZ welcomed the practice of only heating the living room. It gave them more family time, as the kids gravitated to the warm room, rather than to their bedrooms.
It also made me realise how much smarter we could be about using our heating systems. Roll on the day when sophisticated controls come as standard. In the meantime, each radiator does have an on and off setting - maybe we should use them more!
If you have a question about anything in the above blog, please ask it in the comments section below.
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