UFH to be connected to ASHP ?

[newtoallthis]

I am the OP updating things.

Having spoken to a couple of suppliers it looks very much that I will be able to claim the Boiler Upgrade Grant.

I have been doing a bit of experimenting with my UFH manifold and it looks like there is a complication with my requirements.

If the proposed ASHP were to be connected directly to the manifold then the flow through the Heat Pump would be the sum of the individual zone flows, at the moment the design sum of the flows is around 7-8 ish lpm. This is very low and it doesn't look like many, or even any, heat pumps would be happy with a flow this low. This flow, with a 5C dT would require a pump able to run at around 2.5KW, any offers as to a make/model of heat pump that would be happy with this ?

Without decent intrumentation it is not possible to measure the actual dT across the manifold, but using an IR Temp indicator it looks like with a cold slab it might be in the range 5-7C - as I understand it, if I have to increase the flow through the zones to achieve a number acceptable to the available heat pumps, then the dT will decrease and I might (will ?) struggle to achieve the necessaty dt of 5C that all the manufacturers require.

My heat demand is likely in the range 0.5-2kw, but as I am planning to run the pump at the times with lowest electricity prices, then maybe the pump will have to operate at a higher output and hence a 5kw pump might be the right size.

Am I right to be concerned about low flows and if so, how much will increasing the flowrates have an impact on the dT ?

TIA
P

[Stinsy]

I am the OP updating things.

Having spoken to a couple of suppliers it looks very much that I will be able to claim the Boiler Upgrade Grant.

I have been doing a bit of experimenting with my UFH manifold and it looks like there is a complication with my requirements.

If the proposed ASHP were to be connected directly to the manifold then the flow through the Heat Pump would be the sum of the individual zone flows, at the moment the design sum of the flows is around 7-8 ish lpm. This is very low and it doesn't look like many, or even any, heat pumps would be happy with a flow this low. This flow, with a 5C dT would require a pump able to run at around 2.5KW, any offers as to a make/model of heat pump that would be happy with this ?

Without decent intrumentation it is not possible to measure the actual dT across the manifold, but using an IR Temp indicator it looks like with a cold slab it might be in the range 5-7C - as I understand it, if I have to increase the flow through the zones to achieve a number acceptable to the available heat pumps, then the dT will decrease and I might (will ?) struggle to achieve the necessaty dt of 5C that all the manufacturers require.

My heat demand is likely in the range 0.5-2kw, but as I am planning to run the pump at the times with lowest electricity prices, then maybe the pump will have to operate at a higher output and hence a 5kw pump might be the right size.

Am I right to be concerned about low flows and if so, how much will increasing the flowrates have an impact on the dT ?

TIA
P

The solution is “close coupled ts”. Basically you have one pump getting the water wizzing round your UFH really fast, this provides an even floor temp which increases comfort levels, and the HP has its own pump doing its own thing.

Loads of explanations on youuuuuuchoooob.

[Fintray]

I have been doing a bit of experimenting with my UFH manifold and it looks like there is a complication with my requirements.

If the proposed ASHP were to be connected directly to the manifold then the flow through the Heat Pump would be the sum of the individual zone flows, at the moment the design sum of the flows is around 7-8 ish lpm. This is very low and it doesn't look like many, or even any, heat pumps would be happy with a flow this low. This flow, with a 5C dT would require a pump able to run at around 2.5KW, any offers as to a make/model of heat pump that would be happy with this ?

Without decent intrumentation it is not possible to measure the actual dT across the manifold, but using an IR Temp indicator it looks like with a cold slab it might be in the range 5-7C - as I understand it, if I have to increase the flow through the zones to achieve a number acceptable to the available heat pumps, then the dT will decrease and I might (will ?) struggle to achieve the necessaty dt of 5C that all the manufacturers require.

My heat demand is likely in the range 0.5-2kw, but as I am planning to run the pump at the times with lowest electricity prices, then maybe the pump will have to operate at a higher output and hence a 5kw pump might be the right size.

Am I right to be concerned about low flows and if so, how much will increasing the flowrates have an impact on the dT ?

TIA
P

Both the 3.5 and 5.0kW Vaillant Arotherm models have a minimum volume flow requirement of 400l/hr which would match your UFH settings. I wouldn't get to worried about the DT being 5C, I tried to get mine to this but couldn't get it above 2-2.5C.

It would be best for efficiency to run your heat pump 24/7 rather than try to only run it during the cheap rate (generally the coldest part of the day), a lot of the time the HP will be modulating down and using less than 1kW.

[newtoallthis]

Indeed, I am conscious of the advantages of running 24/7, but it will probably boil down to the economics, if it's much cheaper to spank heat into the house for a short period during low electricity prices then that's probably what I will do.

I am hoping that I can manipulate the flow to around 8+ lpm and this should mean no problem with minimum flowrates.

One supplier has already offered a cost to me of £0 is I choose a Samsung R290 heat pump and less than £500 if I go with Vaillant.

Does the forum have a view of the relative merits of these two brands.

[AE-NMidlands]

Indeed, I am conscious of the advantages of running 24/7, but it will probably boil down to the economics, if it's much cheaper to spank heat into the house for a short period during low electricity prices then that's probably what I will do.

I haven't even started down this road yet, but isn't that treating it like a gas boiler (with a TOU tariff) - exactly what we are advised not to do?

I imagined that with the lower flow temp than a boiler there's almost no chance of getting the house warm enough to last through the day until the next cheap period.

Aren't Octopus special HP tariffs designed to take away this problem? I thought that (like EV tariffs) HP people got dirt cheap power for a lot longer than me on my Flux cheap period...

[Stinsy]

R290 HPs don’t seem to lose power output in low temps compared with R32. Hard to know for sure, not seen real world data, just looking at manufacturer figures.

I wouldn’t recommend running the HP hard for space heating unless you have UFH beneath a 200mm slab. Comfort levels will be poor due to the temperature fluctuation. Better to run the HP low-and-slow 24/7 even if that means paying for peak electric.

[newtoallthis]

Indeed, I am conscious of the advantages of running 24/7, but it will probably boil down to the economics, if it's much cheaper to spank heat into the house for a short period during low electricity prices then that's probably what I will do.

I haven't even started down this road yet, but isn't that treating it like a gas boiler (with a TOU tariff) - exactly what we are advised not to do?

I imagined that with the lower flow temp than a boiler there's almost no chance of getting the house warm enough to last through the day until the next cheap period.

Aren't Octopus special HP tariffs designed to take away this problem? I thought that (like EV tariffs) HP people got dirt cheap power for a lot longer than me on my Flux cheap period...

We have a very thck slab, and an extremely well insulated house, I expect (and only time will tell) that I can heat the house for 6-8 hrs and it will then stay warm for well over 24 hrs.
It will likely boil down to the Electricity contract we are on, at the moment we get dirt cheap electricity from 0:00 to 06:00 and then another 2 hrs of cheap electricity mid morning - this is stupidly inexpensive and it won't last forever.

[newtoallthis]

R290 HPs don’t seem to lose power output in low temps compared with R32. Hard to know for sure, not seen real world data, just looking at manufacturer figures.

I wouldn’t recommend running the HP hard for space heating unless you have UFH beneath a 200mm slab. Comfort levels will be poor due to the temperature fluctuation. Better to run the HP low-and-slow 24/7 even if that means paying for peak electric.

Our UFH is in a minimum of 150mm of screed on top of 100mm of concrete.
The concrete is sitting on 300mm of EPS.
It can store a lot of heat - I just don't really know if it's enough

[Fintray]

Indeed, I am conscious of the advantages of running 24/7, but it will probably boil down to the economics, if it's much cheaper to spank heat into the house for a short period during low electricity prices then that's probably what I will do.

I am hoping that I can manipulate the flow to around 8+ lpm and this should mean no problem with minimum flowrates.

One supplier has already offered a cost to me of £0 is I choose a Samsung R290 heat pump and less than £500 if I go with Vaillant.

Does the forum have a view of the relative merits of these two brands.

With the tariff that you are on you could up the heat input during the night and have a setback temperature during the day, with your batteries and the cheap period mid morning you might manage to run the HP 24/7 cheaply enough.

You should be able to up the flow round you UFH loops easily enough and I wouldn't worry about getting a DT of 5C.

Can't say anything definitive about Samsung v Vaillant but on heatpump monitor there are 17 Samsung HP's v 123 Vaillant HP's out of a total of 275 HP's.

[newtoallthis]

Indeed, I am conscious of the advantages of running 24/7, but it will probably boil down to the economics, if it's much cheaper to spank heat into the house for a short period during low electricity prices then that's probably what I will do.

I am hoping that I can manipulate the flow to around 8+ lpm and this should mean no problem with minimum flowrates.

One supplier has already offered a cost to me of £0 is I choose a Samsung R290 heat pump and less than £500 if I go with Vaillant.

Does the forum have a view of the relative merits of these two brands.

With the tariff that you are on you could up the heat input during the night and have a setback temperature during the day, with your batteries and the cheap period mid morning you might manage to run the HP 24/7 cheaply enough.

You should be able to up the flow round you UFH loops easily enough and I wouldn't worry about getting a DT of 5C.

Can't say anything definitive about Samsung v Vaillant but on heatpump monitor there are 17 Samsung HP's v 123 Vaillant HP's out of a total of 275 HP's.

I was under the impression that delivering a dT of 5C was required in order to minimise cycling of the heat pump - is this not the case ?