ASHP and UFH

[HerbJ]

3 hours ago, Ed Davies said:

Duct cooler?

 

But @Nickfromwales mentioned a duct heater/cooler, I'm assuming as a combined unit. You wouldn't be using the heater with bypass so placing it for heating seems reasonable. Apart from the frost protection possibility I don't see any point in putting a heater or cooler in the inlet (outside→MVHR) duct.

Point taken - I have corrected my earlier response to make sense of my point on cooling. For inlet heating, this is NOT an  uncommon location on some MVHR systems for frost protection, though many like my PAUL NOVUS unit have the frost protection heater mounted internally.

 

Edited April 2, 2019 by HerbJ

[joe90]

3 hours ago, PeterW said:

 

I'd go with some sort of willis type arrangement or even a jacuzzi heater inline with a duct heater - cheaper than an electric heater and also simpler to integrate with an existing heating system I expect

 

As I already have DHW heated by the ASHP near the MVHR unit it would be simple to use that to heat a wet heater within the manifold.?

[PeterW]

Yep ... looking for heat you could always add the heater matrix as another loop on the UFH as long as the temperature is ok. 

[joe90]

1 hour ago, PeterW said:

Yep ... looking for heat you could always add the heater matrix as another loop on the UFH as long as the temperature is ok. 

 

Cant, to late to put pipes from buffer and UFH up to loft, but my DHW tank is just under it ?

[Nickfromwales]

54 minutes ago, joe90 said:

 

Cant, to late to put pipes from buffer and UFH up to loft, but my DHW tank is just under it ?

Then can't you just spur off the flow and return of the cylinder? It would require a bit of nifty setting up, and the installation of 2x 2-port zone valves at the cylinder, but certainly do-able with your current setup IMO.

 

10 hours ago, Ed Davies said:

 

I'd agree with @joe90, that seems a weird thing to do. If the MVHR is 90% efficient, for example, then you'd be throwing away 90% of the heating or cooling achieved via the exhaust duct (MVHR to outside). Much better to put a heater or cooler on the house side of the MVHR presumably in the supply duct (from the MVHR to the house) though there might be reasons to put it in the extract duct (house→MVHR) with only a small loss in efficiency.

In a low energy / PH you are only looking to reinforce the situation by off-setting the impact of the incoming air temp from atmosphere. Some parts of the year the duct 'unit' ( heat / cool / sod-all ) will do nowt. In the extreme it will cool, effectively, and in the coldest snaps it will raise the incoming air temp to compliment the efficiency of the MVHR.

It's a no-brainer to put in the inlet from atmosphere AFAIC, as that's far simpler to implement. It's there to compliment the MVHR H-Ex not replace it

 

[Nickfromwales]

10 hours ago, Pete said:

How do the duct heaters impact on the electricity bill?

Not very much if the heat is wet and derived from an ASHP  

FWIW, I would not recommend an electric unit TBH, as they seem to be less 'gentle' in the heat delivery and a bit more 'noticeable' in the air. Electric units usually pass the set point of the thermostat, with a far coarser hysteresis from a thermo-mechanical control device, so are nowhere near as favourable as bringing in the heat via a wet source. 

[joe90]

17 minutes ago, Nickfromwales said:

Then can't you just spur off the flow and return of the cylinder? It would require a bit of nifty setting up, and the installation of 2x 2-port zone valves at the cylinder, but certainly do-able with your current setup IMO.

 

Thats what I thought ?but judging by this winter it would only be used fir a few weeks or a couple of months tops so I wonder if it’s worth the bother ? It’s certainly not on my urgent to do list but will consider it for next winter.

[Nickfromwales]

39 minutes ago, joe90 said:

 

Thats what I thought ?but judging by this winter it would only be used fir a few weeks or a couple of months tops so I wonder if it’s worth the bother ? It’s certainly not on my urgent to do list but will consider it for next winter.

Agree it would be a bit of upheaval, but it is a cheeky way of getting a little uplift if you've already got an ASHP.  

My comments are referring to instances when things are still open to change in design, eg before things are fitted, but 'chopping something in' retrospectively can usually still be facilitated with a bit of tenacity. 

[moldy]

On 01/04/2019 at 09:58, le-cerveau said:

 

For the sake of putting it in and the minimal cost compared to trying to retrofit something, I would include UFH in both floors, even if you don''t use it initially.  You can at a later date set up the slab cooling for both floors.

 

I have piped in both floors >400m², the house is passive standard (un-certified) and you cant tell if the heating is on or not as it is so gentle (UFH flow temp of 26^oC) however last summer when it was extremely hot (house just finished) the slab cooling did come on for a few days, usually in late afternoon and of you touched the floor near the manifolds you could just about tell it was cooling, but it had the desired effect in keeping the house livable.

Could you point me towards some systems that combine UFH and UFC (cooling) - I'm having trouble finding any.

[Jeremy Harris]

1 hour ago, moldy said:

Could you point me towards some systems that combine UFH and UFC (cooling) - I'm having trouble finding any.

 

I'm pretty sure that installers have yet to pick up on this.  AFAIK, it's probably only members of this forum that have discovered that floor cooling can be pretty effective in hot weather.  Perhaps we're pioneers, in which case I suspect we might be collectively recognised as such when installers catch up with some of the things we are doing, in years to come.

[le-cerveau]

12 hours ago, moldy said:

Could you point me towards some systems that combine UFH and UFC (cooling) - I'm having trouble finding any.

 

I did a custom setup  as have most here.  My pipes were installed by warmafloor but the setup and control is all custom designed and installed.

[Ed Davies]

Worth mentioning that, AIUI, ASHPs installed for the RHI ought to have the cooling function disabled which is probably why installers aren't pushing this and wiring systems up for it but that it can usually be re-enabled via a DIP switch or software setting (plus some external control of some sort to call for it).

[Onoff]

So in a low energy house what is the major mistake(s) made that you have to use energy to cool the place in the Summer? Seems a bit wrong to me. Is the house orientation wrong, could more thought been given to natural shading etc?

[Jeremy Harris]

17 minutes ago, Onoff said:

So in a low energy house what is the major mistake(s) made that you have to use energy to cool the place in the Summer? Seems a bit wrong to me. Is the house orientation wrong, could more thought been given to natural shading etc?

 

Solar gain through glazing seems to be far and away the most significant cause of overheating, I think.  Not really surprising, as it's fairly easy to get around 200 W/m² or more coming in through glazing, and for a house that needs no heating at all for a fair part of the year that's a significant amount of heat input.  Even in winter we can really notice the effect of having guests here.  Two people will add around 160 to 200 W of heat, more than enough to push the room temperature up a fair bit.

[Ed Davies]

Any house will need cooling if the outside temperature is above comfort levels for a number of days in a row.

 

But maybe the problem is made worse by too big windows. Large windows can be a net positive for heating over the heating season (though I have my doubts for the worst weeks of the winter) but there are, IMHO, better solutions to getting heat into the house - solar thermal in particular. I think windows should be as small as reasonable for getting light in, outside awareness, means of escape, ventilation (if that makes sense where you are).

[ragg987]

3 hours ago, JSHarris said:

Solar gain through glazing seems to be far and away the most significant cause of overheating

This is the case for us. Our open plan south and West facing kitchen lounge diner suffers a lot, 2 small North facing rooms are fine.

 

3 hours ago, Ed Davies said:

Any house will need cooling if the outside temperature is above comfort levels for a number of days in a row.

Does not have to be active cooling, an option would be to take advantage of cooler air at night by leaving windows open then shutting them in the day and let the MVHR do is thing. But when external temps gets to upper 20s we resort to floor cooling.

 

Edited September 1, 2019 by ragg987

[joth]

On 31/08/2019 at 19:40, JSHarris said:

AFAIK, it's probably only members of this forum that have discovered that floor cooling can be pretty effective in hot weather

 

Not any more.  I had conversations with 3 installers, and all had setup systems to cool ufh.

Thing is vast majority of installers are MCS registered, and most of them still believe RHI outlaws active cooling, hence their aversion. Happily the first one I spoke to clarified this point, but the other two said they'd only do it in non-RHI installs until I pointed out this has changed. (Not that RHI is a crucial deciding point for me, but the 7.7k bung is hard to ignore)

 

Edit to add: active cooling does violate the "permitted development rights" for installing an ASHP; technically if you set it up for cooling you need planning permission for it. This might also put off some installers?

(Also the permitted dev rights only apply to the first heat pump installed on a property)

 

 

Edited September 2, 2019 by joth