Heat exchanger/pump?

Posted: Thu Dec 7, 2017 11:36am

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Stephanie86

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We have a house which is all electric; the hot water is provided by an Ariston air source heat pump, which appears to be extremely efficient, but our query is the hydronic under floor heating. This is powered by a separate York air to water heat exchanger (which apparently can ‘chill’ the floor in hot weather, effectively being a large refrigerator, which reverses operation for providing heat). This heats the liquid in the pipework which is embedded in a concrete slab. The results are magnificent, making this freezing house toasty warm. However, with absolutely no experience of heat exchangers, can anyone advise as to the best way to run it to avoid bankruptcy. We know that indoor thermostats cannot control this kind of underfloor heating as the reaction time of the slab is so slow, needing about 10 hours to warm up - 1 x degree per 40 minutes we understand. We have downloaded the minimal information available online - at a cost - which doens’t really tell us anything useful about operation, consisting of sheets of charts of co-efficients doubtless fascinating to a heating engineer but not to us! The heat exchanger has an ‘ecocontrol’ attached to it, which simply appears to control the temperature of the piped water - currently around 35 degrees - but that’s all. There is a remote switch in the house, which we have discovered can turn the machine on or off without having actually to go outside. Does one simply control it by this - say, allowing it to heat up overnight, then, hypothetically, turning it off during the day whilst the floor equally slowly releases heat? Any advice would be appreciated as we have absolutely NO idea about how much it costs to run or how we are supposed to use it most effectively. We have been given scare stories that it is simply unaffordable, but cannot of course live without any heating at the moment. We do have a very efficient new wood burner, but that really doesn’t heat the entire house and our ground floor is completely open, so the kitchen is freezing.

Most advice has been to rip it out and install a gas boiler with all that that entails, but that seems rather drastic as the HW seems perfectly reasonable and the capital expenditure to completely revamp the system could outweigh the running costs?

Would be grateful to anyone with knowledge - apologies for going on at such length!

Stephanie

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Posted: Thu Dec 7, 2017 3:04pm

Stephanie86

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Posted: Thu Dec 7, 2017 3:04pm

Thank you for your reply, Pete.

Yes, will try to obtain multimeter to get an idea.

the water temperature would appear to be the norm for this type of system, as far as I can understand from my researches online - which mainly, admittedly, relate to North America and Canada! There doesn’t appear to be any information about them locally, despite, allegedly, them being commonly used in Europe.

Yes, on the cheaper energy nighttime tariff- which currently seems to run until midday. Will try ‘topping it up’ in the afternoons, but it heats up so slowly that that may not have much effect. Am wondering about trying to put a timing mechanism on the indoor ‘on/off’ switch.

Thanks, Stephanie

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Posted: Thu Dec 7, 2017 7:32pm

Kelvin1960

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Posted: Thu Dec 7, 2017 7:32pm

Stephanie86 wrote on Thu Dec 7, 2017 11:36am:
We have a house which is all electric; the hot water is provided by an Ariston air source heat pump, which appears to be extremely efficient, but our query is the hydronic under floor heating. This is powered by a separate York air to water heat exchanger (which apparently can ‘chill’ the flo...

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...or in hot weather, effectively being a large refrigerator, which reverses operation for providing heat). This heats the liquid in the pipework which is embedded in a concrete slab. The results are magnificent, making this freezing house toasty warm. However, with absolutely no experience of heat exchangers, can anyone advise as to the best way to run it to avoid bankruptcy. We know that indoor thermostats cannot control this kind of underfloor heating as the reaction time of the slab is so slow, needing about 10 hours to warm up - 1 x degree per 40 minutes we understand. We have downloaded the minimal information available online - at a cost - which doens’t really tell us anything useful about operation, consisting of sheets of charts of co-efficients doubtless fascinating to a heating engineer but not to us! The heat exchanger has an ‘ecocontrol’ attached to it, which simply appears to control the temperature of the piped water - currently around 35 degrees - but that’s all. There is a remote switch in the house, which we have discovered can turn the machine on or off without having actually to go outside. Does one simply control it by this - say, allowing it to heat up overnight, then, hypothetically, turning it off during the day whilst the floor equally slowly releases heat? Any advice would be appreciated as we have absolutely NO idea about how much it costs to run or how we are supposed to use it most effectively. We have been given scare stories that it is simply unaffordable, but cannot of course live without any heating at the moment. We do have a very efficient new wood burner, but that really doesn’t heat the entire house and our ground floor is completely open, so the kitchen is freezing.
Most advice has been to rip it out and install a gas boiler with all that that entails, but that seems rather drastic as the HW seems perfectly reasonable and the capital expenditure to completely revamp the system could outweigh the running costs?
Would be grateful to anyone with knowledge - apologies for going on at such length!
Stephanie

We have a flat in England with floor slab heating and room thermostats. The floor slabs are heated by off-peak electricity (not a heat pump), but the principle is the same.

There is a knack to using it .... the trick is to slightly "overheat" the room during the off-peak periods, to enable a slow decay of temperature during the on-peak periods, such that it is just getting chilly as the off-peak period comes round again. The floor slab has a very high thermal mass; it works like a huge electric storage heater.

It isn't easy, and it takes a bit of experience/practice. You set an internal thermostat to cut off at the "overheat" point, and you set it higher as the weather gets colder (keeping an eye on the weather forecast) and vice versa. There is no "set and forget" option.

So, if that arrangement transfers to yours, it seems that a time clock is needed to limit running of your heat pump to the off-peak periods (preferably with a manual override), and an internal thermostat.

It takes 2-3 days for this system to work properly after switching it on - the time taken for the slab to warm up thoroughly.

With Iberdrola, the peak rate is currently from around noon to 10pm, so your floor slabs could probably hold the house at a stable temperature.

As per a previous response, heat pumps are very efficient (you only pay for 30-40% of the heat you get), but there is a compressor to wear out.

Regards.

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Posted: Fri Dec 8, 2017 9:37am

Stephanie86

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Posted: Fri Dec 8, 2017 9:37am

Kelvin, thank you for your comprehensive reply. To a degree it reinforces what we had thought - ie run it at the night time cheaper rate (Iberdrola) and switch off during the day, so will experiment further.

There are no room thermostats existing and I have a feeling that attempting to install them to control the heat exchanger would be v complex - the on/off switch may be easier, especially if we could fit a timer to it somehow.

Am still considering what to do - it doesn’t respond quickly enough to be used ‘intermittently’ for the odd really cold day now and then.

Many thanks

Stephanie