Topic: Heap Pump/UFH - Early morning temp

Heap Pump/UFH - Early morning temp 

We have moved into a new house in Auckland. It is block with concrete floors and extremely well insulated. It has UFH, powered by a heat pump, which was installed by the person we bought the house off.

There is a control panel in the house where we set night and day temp – which in turn powers up a control panel for the heat pump (where I can adjust water temp for the UFH). The house heats up a lot during the day. At 8pm the house will still happily be 21 deg. My problem is that in the mornings it will be 17-18 deg. depending on the day, and there’s no way I can really warm the concrete pad up even if I have the UFH coming on at 4am.

So ironically, because I don’t need the UFH during most of the day, I can’t really use it for the time I need it...

I know UFH is best used to provide an ongoing low level heat but I just don’t need anything for most of the day. I’m not sure what others do in this situation? (Other than have a more appropriate heating system!)

One option would be to set the heat pump controller to say 28 degrees and have the thermostat in the house set very high so it stays on even when the house gets to 21 deg – and set it to come on between 4am - 10pm so I keep the pad reasonably warm so as to take the edge off in the mornings. (I have it set to “night” settings at 10pm so that it turns off and doesn’t keep the neighbours awake). However, this all seems a bit inefficient.

Keen to hear your thoughts....

Re: Heap Pump/UFH - Early morning temp 

One presumes you are using a air thermostat, not the right stat for this type of installation.
So turn it up high or wire it out.
With underfloor (presume deep embedded)
So the heat you are putting in does not come out for some time. So run the heat pump during the day
(it will not over heat) and turn of at late at night.
Set water temp to a level that you feel comfatable with

Re: Heap Pump/UFH - Early morning temp 

Thanks for this. That's interesting, but may explain why someone once explained that this was an "odd" setup...(and yes, it is embedded in the concrete pad).

Okay - it appears to be as I thought: in order to address the issue we have in the morning, I need to run the heat pump during the day (when technically we don't need the heat) to bring the pad up in advance of the morning's need for heat. Not all that efficient but presumably a result of the setup we have (and also clear winter days when there is much greater variation in temp as between day/evening and first thing in the morning).

I guess then my next question is whether I'm best to just run the heat pump in the late arvo'/evening to bring the pad up to temp or whether it's more efficient to basically keep the pad 'topped up' during the day by leaving the heat pump on all day? I take it that I'm better to run it all day?

Re: Heap Pump/UFH - Early morning temp 

You are missing the point.
I grow firewood when I do not need heat, I do this so I can have firewood when I do need heat.
You heat the floor so that it comes out when the air becomes cold. Your floor is a thermal store. do not think of the heat pump as your heater, the floor is the heater

Re: Heap Pump/UFH - Early morning temp 

I'm here to learn.

So on the assumption there is obviously some energy (and hence cost) required to keep the floor warm, you're saying that this energy is minimal when the ambient temp is warm because the pad itself will lose little heat, and when the ambient temp drops then the pad will lose more heat, which is actually what we want because that heat will radiate into the house (assuming the pad's reasonably well insualted on the base and sides)?

Re: Heap Pump/UFH - Early morning temp 

perfect trevor

Re: Heap Pump/UFH - Early morning temp 

Thanks for all of this, it’s been most helpful.

I guess my (hopefully!) final question is this: given I unfortunately do not have an in-pad thermostat, what sort of proxy could I use to try and keep the pad at a reasonably steady temp? What I don’t want to do is keep running the heat pump all day when the pad is warm enough, e.g. because the sun is shining directly onto most of the pad (which happens during clear days from around 10-3pm). I only have two variables I can control: (1) the air thermostat trigger point to turn on the heat pump; and (2) the heat pump water temp. Am I right that there would always be some temp loss as the water cycles through the tubes in the UFH, i.e. a 30 deg ex-heat pump water temp will always be a bit higher than the return temp and hence the heat pump would constantly need to keep working (at least to some extent) to keep the water temp at 30deg, irrespective of how hot the pad itself was? Or would it be the case that the warm pad may well keep the water temp at 30 deg for reasonable periods of time?

Assuming the water will always need to be topped up to 30 deg, I guess I could set the heat pump water temp to say around 30deg and have the thermostat set so that the heat pump was on from say 6am-11am, 2-4pm, and then 6pm-10pm (and play around with those timings to mimic what would be needed to keep the pad around a semi-constant temp) – accepting that at night it will fall a bit more given the ambient temp drop and 8 hour period of no heating?

Thanks for all the help with this.

Cheers

Re: Heap Pump/UFH - Early morning temp 

You should be controlling your heat pump with return water temperature. "The water that comes out of the floor"
If the floor is warm from the sun then the water leaving the floor is going to be warm. This way you do not over heat.
This method ensures the concrete remains warm.
I would start with about 26C then move up if required, only by 1C per couple of days.
I would ideally run it all the time, but I understand that you can not because of the noise, so only turn off on the timer when the noise is an issue.
Keep it running all day, you only think the pad is warm enough, if it is it will turn of automatically.
If it is not it will run.
This gives you the thermal store.
Running in the middle of the day is very efficient.
If you have a hot spot due to solar gain then this will be transported throughout the whole floor.
Again you are not grasping the point, the heat produced comes out later.

Re: Heap Pump/UFH - Early morning temp 

I am currently looking into putting this kind of system into a new house and am really interested in the information provided here. I have read about in-pad thermostats being better, but when I spoke to a company that designs and installs these systems they told me that a air thermostat works just as well. Are you saying that the thermostat should actually be measuring the return water temp for the HWHP control to get a better result?

Re: Heap Pump/UFH - Early morning temp 

Hi Tank, The first question i must ask, are you looking for an instaneous heating system (surface mounted pipes and hottish water) or are you looking at a thernal store type system "deep embedded" (runs most of the time)
TC