Which ASHP are set up to cool

[joth]

Great, Fascinating ideas. Future proofing a spare loop to the loft sound ideal, as from there we'll have easy access to mvhr, loft itself, bedrooms and the vaulted hall light well. Cold air falls so we can drop it down onto any those areas relatively easily.

 

 

[jfb]

this is all great info.

 

i was doing a bit more digging around and came across a heat pump site that was giving reasons against using the heat pump to cool:

https://www.freedomhp.co.uk/2018/10/08/why-cooling-is-so-hard-to-achieve-in-a-conventional-heating-system/

 

it claims it is very inefficient (8x compared to heating) and also that it can lead to problems of condensation.

has anyone using a slab to cool experienced this (a cool damp floor)? or is it likely to be less relevant if the pipes are spaced close together so you are not asking for a big differential between outside temp and slab temp (in same way as heating can be done at lower temps if pipes are closely spaced)

[ProDave]

A lot of the people that use a heat pump for cooling in summer, have solar PV fitted, so the efficiency is not very important when there is plenty of free electrcity being produced by your solar PV when it needs to do cooling functions.

 

Agreed if you don't have PV then you would be paying for that so it would be more of an issue.

[Jeremy Harris]

22 hours ago, jfb said:

this is all great info.

 

i was doing a bit more digging around and came across a heat pump site that was giving reasons against using the heat pump to cool:

https://www.freedomhp.co.uk/2018/10/08/why-cooling-is-so-hard-to-achieve-in-a-conventional-heating-system/

 

it claims it is very inefficient (8x compared to heating) and also that it can lead to problems of condensation.

has anyone using a slab to cool experienced this (a cool damp floor)? or is it likely to be less relevant if the pipes are spaced close together so you are not asking for a big differential between outside temp and slab temp (in same way as heating can be done at lower temps if pipes are closely spaced)

 

Not sure that the real-world facts support the views in that article, TBH.  Our ASHP seems to run with a COP of around 4 when in cooling mode, based on measurements of how much power it uses and the output flow temp and rate.  That means it's pretty much as efficient when cooling as when heating.

 

We run our ASHP at around 10° to 12°C in cooling mode, and that cools the surface of the floor to about 17° to 18°C (it rarely drops below 18°C though).  There's zero condensation, and I wouldn't expect any, as the humidity in the house would have to be around 80% for that to happen, and in hot weather we rarely see the humidity get above 50%, most of the time it's around 35% to 40% at most.

 

We've been cooling the slab in hot weather for several years now, without any problems, and at near-zero cost, as the PV system provides over 90% of the energy needed to run it. 

[SteamyTea]

22 hours ago, jfb said:

i was doing a bit more digging around and came across a heat pump site that was giving reasons against using the heat pump to cool:

The seemed to be really selling fan coils as an extra.

[Nickfromwales]

On 23/05/2019 at 21:16, joth said:

Great, Fascinating ideas. Future proofing a spare loop to the loft sound ideal, as from there we'll have easy access to mvhr, loft itself, bedrooms and the vaulted hall light well.

Following this with interest....

I am part-way through installing all of the M&E stuff for @MarkA and the core of the heating will be via an ASHP. Mark asked from the outset for cooling, both in the slab and more specifically in the bedrooms also, so I've started off by getting piped for that a-la @JSHarris's install eg to provide slab cooling, as the first line of 'defence'. The flow and return pipes have been extended to both the attic plant, ( above the bathroom that divides bed 2 and bed 3 ( vaulted ceilings )), and the small cupboard space left in the eave of bed 1 where each space will house a single, dumb,  duct cooler dedicated to each room. They have been further extended to the ground floor plant room to allow for cooling to be retrospectively added to the one downstairs bedroom ( 4 ) if the need ever arises ( or to inject a bit more heat for that matter ).

Bed 1 & 3 catch the southern sun, bed 2 is on the opposite side, as is bed 4, so the biggest dilemma is to manage the cooling 'per room' as opposed to 'all on / all off'. We've allowed for heat / cool capable room stats per ( bed ) room so these can be individually brought in / out of play according to the effects of the solar gain.

 

On 23/05/2019 at 21:16, joth said:

Cold air falls so we can drop it down onto any those areas relatively easily.

My thoughts, ( yet to be proven ). So what I have done is run 2 more 92mm MVHR ducts from the duct cooler, then under the floor and back into each bedroom, as a cooled air re-circulation setup, where the fan at the duct cooler will blow cooled air directly into the ( part-lowered but still vaulted ) ceiling sections where the warmest air will stagnate. I have then installed a single air extract point at each opposite end of the room, down at a little lower than socket level, where the air gets 'sucked' back up to the duct cooler for cooling and re-introduction to the room. 

Concerns would be that if the slab cooling mandates the ASHP 'cooling temp' being as low as you say Jeremy, then will there be a risk of getting condensate collecting in the return lines? I was thinking not, as by then the extract air temp will have been lifted by the effects of collecting the unwanted heat from the room. As far as stagnation, that will be dealt with by the fact that these systems are auxiliary and will work alongside the standard MVHR which will continuously reintroduce fresh air.  

I will choose fans which have 3 speeds, handled by the wall mounted stat / ctrl to keep the controls as dumb ( K.I.S.S. ) as possible. That will be the means of dictating how much or how little cooling is employed at any one time. The idea being that speed 1 would be quiet enough to sleep with, and speed 3 would give you a decent 'breeze'. All theoretical until I switch it on, but I'm ( very ) quietly confident.

 

Discussions have been about prevention being better than cure, so to manage the heating ( cooling ) effectively it seems best to address it before it becomes problematic. This can be managed, effectively I hope, in one of two ways;

1) Don't let the rooms get too hot before introducing the cooling system....."Simple!"

So, predict if you need to boost cool, eg if you know it's going to be a sunny aka problematic midday / late afternoon then you can simply hit a boost controller to force run the cooling side of the system PRIOR to the hysteresis of the stat detecting the increase. It's quite obvious when you're in a 'passive' house ( well insulated / airtight in other words ) and the sun is up and at 'em.It gets warm, and it does it quite quickly, which means the cooling would have to fight to bring the temp down after the stat failed to predict the degree of heat rise and 'set-back' according to it's pending impact. Now to revert to the prevention technique, that can't really be done autonomously unless you have a weather-predictive what-not an an entry-level home automation system with some basic intelligence, but there is, as I say above, the ability to just give it the human touch. Simple, and free. If you're in, use your noggin, if you're planning a day out, give the house a 4 hour boost ( £20 time-clock will suffice ) and have the cooling system run to offset the additional heat gain. Results, house never gets to the problematic heat level, and the fabric of the dwelling stays close t, or at, the comfort / desired ambient temp.

2) Weather compensation. I have decided to re-invent this a little after seeing @Barney12's BPC duct cooler in his MVHR intake from atmosphere. That is connected to a 'geothermal' brine loop that simply, very simply actually, recirculates the temp of Terra-Firma to the duct cooler. A bit of uplift when the outside air temp gets very low, and vice versa. Better than nowt but could be improved ( but remembering firstly that @Barney12 doesn't have an ASHP so this geothermal option had significant attraction ). 

Ok, that said, when I fitted the SA ( Sunamp ) units there I decided to give this ( already previously installed ) setup a kick in the dangle-berries. I stripped it all back, introduce a PHE ( plate heat exchanger ) and a flip - flop ctrl system so heat could be injected into the duct cooler from the SA if the outside air temp got ridiculously low ( Dartmoor ). Worked rather well if i might say so.

     

Ignore the clutter, Einsteins desk on a good day  

 

Ok, continuing point 2).....

The whole point of a comfortable home should be, that you can wake up and not know if its summer or winter IMO, so that said, we go back to 'weather compensation'. In Mark's I intend to fit ( probably a pair of ) the above duct cooler unit(s) with the specific intention of getting outside air as close to a constant 20.5^oC as possible. They will be installed in the inlet from atmosphere, immediately prior to the MVHR unit. FYI, as Mark will have an ASHP we have not gone to the added expense of an MVHR unit with internal heat pump as that's a minimum uplift in cost of £2k. The idea being not to introduce a problem in the first place and then have to deal with it afterwards with a significant separate additional system. That said there is still merit in having cooling in the bedrooms IMO even with such a core prevention strategy in place, BUT,  with that preemptive measure in place, the auxiliary systems can be dialled back and made far simpler / lower spec etc and thus have less impact on the inhabitants eg from from noise pollution etc caused by being forced to run such auxiliary systems at full wallop.

 

Homework for this weekend includes looking for some decent units and looking at the max airflow rates through them to decide what will have near zero impact on the air intake path to the MVHR ( hence my thoughts to parallel two units and be done with it ).

 

"Seems like a nice, straightforward job"...................... 

   

[le-cerveau]

When I was designing my system (3 years ago) I looked at adding a duct cooler as well as slab cooling and to overcome the problem of condensation I planned on running the ASHP (in cooling) at about 8^oC but using a thermostatic to provide warmer 16^oC to the slab.  Doing this by providing the UFH return to the hot side and the ASHP to the cold side, and utilising a hydraulic separator to balance the pressure.

 

This was one of my original layouts.

The TMV would draw enough cooled water to reduce the return to the desired level, whilst allowing the duct cooler maximum power.

The ESBE TVA572 series of valves have an option down to 10-30^oC control which would work (confirmed with them) or could utilise an electronic controller I use a CRA110 controller on a VRG 130 mixing valve to control my UFH (I run it at 26^oC), but it goes down to +5 so could be used as a cooling control.

 

It is a complication but to maximise duct cooling whilst avoiding floor condensation it is an option.

 

[Nickfromwales]

38 minutes ago, le-cerveau said:

The TMV would draw enough cooled water to reduce the return to the desired level, whilst allowing the duct cooler maximum power.

That's the ESBE valve I have to fit if using a SA for pre-heat to a WB combi, so I'm aware of them, just the thought never crossed my mind to use one there to max out for the duct coolers. Noted, and appreciated, thanks.

 

[Jeremy Harris]

In practice, I've found that there's no problem with running a flow temperature of around 10° to 12°C directly into the UFH for cooling.  The floor surface temperature is the critical thing, and this never seems to get below 17° to 18°C, and so never attracts condensation.

 

With an air temperature of 22°C and a floor temperature of 17°C the humidity would need to be about 73% to start to cause condensation on the floor, and we never see more than about 55% inside the house, and then only in cool, damp, weather.

 

With a room temperature of 22° the floor surface could be safely cooled to about 14°C, as that would need an RH of about 61% in order to create condensation.  If the room was warmer, say 24°C, then for a maximum RH of 60% the floor surface could be cooled to about 16°C, more than enough to provide very effective cooling in most cases.

 

For a belt and braces approach, it might be an idea to measure the RH and use that to set the minimum flow temperature.  This would allow the floor surface to be cooled to, say, 13°C for a room temperature of 24°C and RH of 50%.

[jack]

On 27/05/2019 at 08:18, JSHarris said:

In practice, I've found that there's no problem with running a flow temperature of around 10° to 12°C directly into the UFH for cooling.  The floor surface temperature is the critical thing, and this never seems to get below 17° to 18°C, and so never attracts condensation.

 

I use a flow temp as high as 16°C and that seems to work fine.  

 

That article is BS. At the temps we run, I barely get a mist of condensation on the small amount of exposed metal pipework around the UFH manifold. It doesn't even generate enough to drip onto the floor. I doubt the floor temp falls much below around 20°C, so definitely no condensation there. I don't even bother with a thermostat - just turn cooling mode on when the weather gets hot enough for long enough, and program it to run when the sun's up so it's mostly powered by PV.

[Ed Davies]

From the article:

 

Quote

How about under floor heating? If we cool the floor more than a few degrees it too will sweat, the colder it gets the wetter the floor gets. So you get cold, wet floors. Underfloor heating has another party piece, cold air doesn’t rise, it sits on the floor, so you have to lie on the floor to cool down (and get wet).

 

If there's really a pocket of cool air on the floor (I'm sceptical) then there will be a very limited amount of water vapour available to condense so these two statements are contradictory.

[ragg987]

I keep our cooling flow no cooler than about 12C out of the Ashp, but the output from our buffer to the floor will be higher, possibly about 14 or 15C, as there is an unavoidable mixing effect in the buffer. There is a slight mist on exposed copper. I have insulated the Ashp circulation pump and pipework as well as fitted a drip tray, as per specification.

 

I find that cooling the floor to cool the room works, but we get a slightly damp feel to the room, possibly what the pocket of cool air on floor refers to. I did not see any condensation or damp patches on the floor

[ragg987]

On 25/05/2019 at 10:13, jfb said:

it claims it is very inefficient (8x compared to heating)

I can see why you would infer that from the article, but I do not think that is what it is claiming. It is saying that the heat emitter is sized to heat at 25C above room level, but only cool at 12C below room level, which accounts for 2 of the 8 times less efficient claim. The rest is about solar gain etc which is right but is the reason why you are cooling. So a daft conclusion made based on sensible factors.

 

In a low energy house you would not have 45C heating with ufh, ours runs between 23 and 30C depending on external temp.

 

An Ashp is less efficient cooling compared to heating, but you are talking about a drop of COP from 4 (heat) to 3 (cool), so still efficient.

 

[le-cerveau]

38 minutes ago, ragg987 said:

On 25/05/2019 at 12:13, jfb said:

it claims it is very inefficient (8x compared to heating)

I can see why you would infer that from the article, but I do not think that is what it is claiming. It is saying that the heat emitter is sized to heat at 25C above room level, but only cool at 12C below room level, which accounts for 2 of the 8 times less efficient claim. The rest is about solar gain etc which is right but is the reason why you are cooling. So a daft conclusion made based on sensible factors.

 

In a low energy house you would not have 45C heating with ufh, ours runs between 23 and 30C depending on external temp.

 

An Ashp is less efficient cooling compared to heating, but you are talking about a drop of COP from 4 (heat) to 3 (cool), so still efficient.

 

There are some fundamental issues here:

1. a ΔT of 25^oC for 'normal' operation is for a house that leaks like a sieve.
2. In a house that leaks like a sieve solar gain is not such an issue until the outside air is above about 20^oC.
3. A house that leaks like a sieve will not have MVHR (or is fitted but completely ineffective).
4. A cooling ΔT of 12^oC(below required temp) in a leaky house would probably work for an external temperatures of about 30^oC.

This is all based about heating/cooling the air mass as it changes so fast in the leaky house.

In most of ours well built houses (not leaky) the air is only a part of the problem, not the whole problem.  We maintain the structure (not Thermal Mass) of the house at around the desired temperature and the air follows suite, assisted by MVHW and structure.

 

I have found that most UFH companies cannot get their head around low temperature UFH in passive style houses so do we really expect cooling companies to be any better.  They are geared around provide to the mass market (garbage houses) a common system that a simple instillation man can install (I didn't call them engineers).

 

I had similar issues trying to convince MVHR companies (modern technology) to deviate from their standard patter (2 x MVHR units, cistern extract, multiple vents, specific routing)

 

[ragg987]

25 minutes ago, le-cerveau said:

a common system that a simple instillation man can install (I didn't call them engineers).

## beef mode on ##

 

Technician or trades person, which covers 99% of the people who come into your house to fit or fix stuff.

 

I am an engineer but could not fit most of this stuff.

 

## beef mode off ##

[Jeremy Harris]

The temperature differential relationship with regard to cooling should be broadly similar to that for heating.  Yes, more cooling power is needed than heating power for sure, as it's easy to get a few kW of solar gain, and for a house that only needs maybe 1kW of heat in winter the overheating effect from solar gain may well be significantly greater, hence the need for more cooling. 

 

However, we rarely need to heat the surface of the floor with our UFH above about 23° to 24°C in cold weather.  Cooling the floor to around 18°C draws a fair bit more heat out of the house than we put in from heating during the winter. (~4°to 5°C temperature differential for cooling versus ~1° to 2°C temperature differential for heating) .

[MrMagic]

Slightly OT but it will be interesting to understand the cost per room of a ducted fan coil+ducting+grilles+pipework+thermostat+labour etc Vs a mini-split. This probably warrants a thread of it's own but as I'm not planning on installing anything soon, would be good to just understand an approx cost from @Nickfromwales for the above job.

 

For comparison my most recent mini-splits were approx £1000 per room all in.

 

[Nickfromwales]

57 minutes ago, MrMagic said:

Slightly OT but it will be interesting to understand the cost per room of a ducted fan coil+ducting+grilles+pipework+thermostat+labour etc Vs a mini-split. This probably warrants a thread of it's own but as I'm not planning on installing anything soon, would be good to just understand an approx cost from @Nickfromwales for the above job.

 

For comparison my most recent mini-splits were approx £1000 per room all in.

 

Don’t the split units require an external fan unit? Plus, my  above solution doesn’t have the bulky office-looking surface mounted unit cluttering up the wall   

[SteamyTea]

On 28/05/2019 at 14:56, ragg987 said:

## beef mode on ##

 

Technician or trades person, which covers 99% of the people who come into your house to fit or fix stuff.

 

I am an engineer but could not fit most of this stuff.

 

## beef mode off ##

well said.

[redtop]

really interesting stuff!  I am still considering my options.  I have gas close by, so be cheap to connect to that.  We also have flat roof and nowhere we can spare as a plant room.  We also cannot have PV (dont ask, just not possible) so no free electric.  Lots of windows but in a wood so lots of tree shade.  We will have to have MVHR as whilst it wont be passive standards it will be far more airtight than building regs require.  We also tend to have windows open a lot ?

 

One thing i cant stand is hot bedrooms! So gas boiler for UFH and DHW and maybe some form of ducted air con for the bedrooms.  Now if i go down this route we could also def get rid of upstairs UFH as on the rare occasion we may need it the air con also heats. so would probably be a cheap system to install.

 

ASHP, nut then there is some outside noise and while i can see there are clever ways to make them work well, without PV the cost of cooling in the summer would be high and i would need to run UFH pipes upstairs as well.  I know Air con is power hungry but then we would only use it for half hour before bed, once asleep who cares ?

[ProDave]

As you may see on another thread, I have just enabled cooling mode on my LG Therma V ASHP.  

 

I probably won't get it done this summer but the longer term plan is to get two fan coil units, one for each of the main bedrooms and connect that into the system to give us cooling in both bedrooms.

[joth]

3 hours ago, redtop said:

really interesting stuff!  I am still considering my options.  I have gas close by, so be cheap to connect to that.  We also have flat roof and nowhere we can spare as a plant room.  We also cannot have PV (dont ask, just not possible) so no free electric.  Lots of windows but in a wood so lots of tree shade.  We will have to have MVHR as whilst it wont be passive standards it will be far more airtight than building regs require.  We also tend to have windows open a lot ?

 

One thing i cant stand is hot bedrooms! So gas boiler for UFH and DHW and maybe some form of ducted air con for the bedrooms.  Now if i go down this route we could also def get rid of upstairs UFH as on the rare occasion we may need it the air con also heats. so would probably be a cheap system to install.

  

ASHP, nut then there is some outside noise and while i can see there are clever ways to make them work well, without PV the cost of cooling in the summer would be high and i would need to run UFH pipes upstairs as well.  I know Air con is power hungry but then we would only use it for half hour before bed, once asleep who cares ?

 

Couple thoughts -

in a well insulated home you can do all the heating overnight from Economy 7 tariff, and the house will retain the temperature through the day.  Even folks with lots of PV have to largely rely on this in the depths of winter, as that's when you need most heating and is when the sun is shining less.

for cooling, you can redirect ASHP to cool via UFH downstairs and into a water-air coil exchanger for upstairs. This is exactly what we're planning.  In terms of cost of running cooling, ASHP vs A/C unit shouldn't  really be any different like for like.  if you setup the A/C just to give a very short-sharp blast where it's needed and don't care it will heat back up fairly quickly it might seem cheaper than doing the whole-house with ASHP,  but with water-air heat exchanger I reckon you could design the ASHP to have exactly the same profile as A/C if you wanted.

 

 

 

(And for kicks: here's me  just three months ago swearing I really was not going to get an ASHP.  That sort of thinking doesn't last long after joining this place)

 

 

 

Edited July 24, 2019 by joth

[redtop]

ille have a look at that, i guess the only thing it wouldnt give me is upstairs heating (other than from MVHR)

[ProDave]

Just now, redtop said:

ille have a look at that, i guess the only thing it wouldnt give me is upstairs heating (other than from MVHR)

Why not? you can have UFH upstairs as well.

[redtop]

3 minutes ago, ProDave said:

Why not? you can have UFH upstairs as well.

of course.  But then i am back to where i started.  With gas close by and no PV to reduce elec costs which option is cheaper / easier to install and run.

 

• ASHP + UFH downstairs and upstairs + water - air coil exchanger for cooling upstairs + hot water tank

V

• combi gas boiler + UFH downstairs + multi-room AC upstairs