[gwd]

> This then leads people to say “heat pumps don’t work” or “heat pumps are expensive to run”

When I was doing some extensive renovations of a house about 7 years ago now (in the UK), we called a company whose main business was to install heat pumps (along with underfloor heating, etc). The person asked me a bunch of questions, and based on the age of the house and the insulation and such, she said, "I appreciate what you're trying to do, but I'm really worried that a heat pump won't be able to heat your house sufficiently on cold days; I'd really recommend that you take the money you'd spend on a heat pump and spend it on better insulation for the house instead."

Given that's their main business, and that she was knowingly turning me away as a customer, I tend to give some credence to her assessment. At least it can't be due to a lack of understanding or bias.

Now that our house is better insulated, I might try again next time our boiler is up for replacement, particularly if I can arrange to get the heat pump to cool the floors in the summertime as well as heat them in the wintertime.

[darkr]

WRT cooling with water based system there are a few of issues:

1. A system that also provides cooling isn’t allowed under the heat pump government grant.

2. You might actually need planning permission for this

3. Especially in a humid environment like the uk, you can end up with condensation and damp issues, which you really don’t want in an underfloor slab install

If you also want cooling, better to go an air-air based system (aka air conditioning)

[phicoh]

The situation with respect to condensation: look at historical data for the dew point during the summer season. That as low as you can get. For example, I'm in The Netherlands and our system is set to 18 degrees Celsius.

The amount of cooling this way is limited. Though the nice thing is that it tends to keep the house cool. There is no cold airflow.

With respect to government grants. Sometimes you can buy units that can only heat to get the grant. But a simple change enables cooling after the unit is installed.

[darkr]

In the UK, dew point highs will peak above 22 degrees multiple times per year, so the safe temperature to cool to is something like 25 degrees.

Might provide some benefits on really hot days, but it’s still uncomfortably warm for working in.

[phicoh]

Do you have any source that it is 22 degrees for the entire UK? That seems unlikely.

There is no reason to set all units to the same value in the entire country.

[eru]

You can also just look up what the dew point is on any particular day, and adjust your temperature.

In general, if you want to save money, you should set your aircon to the highest temperature you can tolerate. We typically operate at 26-28C at home here in Singapore, and our dew point is typically between 24-26C.

The modest reduction in air temperature from 30-33C outside feels amplified, because the aircon also reduces humidity. We also rely heavily on ceiling fans.

[gwd]

25 is fine for me to work in; it's about 27 that I start to need to take stronger measures to cool off.

That said, I'm guessing 22 (or 18 or whatever) is the lowest temperature you can have on the pipes; that wouldn't translate to 22 in the house.

[eru]

Depends on how your aircon is working?

If their working fluid is water, you are right. But most aircons work like fridges, and their pipes don't transport 'cold' by literally having a cold fluid, but by having an ambient temperature fluid that they turn into a gas inside your interior aircon unit (and then later turn back from a gas into a liquid on the outside unit).

The actual pipes are always at pretty much ambient temperatures.

[eru]

> 3. Especially in a humid environment like the uk, you can end up with condensation and damp issues, which you really don’t want in an underfloor slab install

You only end up with condensation issues, if you cool below the dew point.

Here in very humid Singapore our dew point is typically at about 24-26C. If you set your aircon to no less than 26C here, you never have any problems with condensation.

(Any old weather reporting website or app will tell the dew point. Apparently right now as I am writing this comments, it's 12C in London.)