Which ASHP are set up to cool

[le-cerveau]

My set up is very non standard.

My ASHP is effectively dumb and the control system does all the heavy lifting.

 

My ASHP heats my buffer (Sunamp PCM34 blocks, pre UniQ) these are used for DHW pre-heat and domestic heating.

The UFH continuously circulates through a Low Loss header (LLH), if heating is required an EBSE motorized valve switches the flow from the LLH to the buffer, drawing heat through a Thermostatic mixing valve set at 26^oC (buffer at 34-40^oC).  When heat no longer required valve switches back.

The Sunamp is connected to the ASHP and defaults it to cooling mode, a second relay connects to the Heat/Cool/Live of the ASHP , normally it connects the live to the cooling thermostat and if a call for cool comes in then the thermostat completes the circuit, switches on the ASHP in cooling which alters the ASHP supply valve from Buffer to LLH..  If however the SunAmp needs heat, this relay is switched, isolating the cooling thermostat (ending call for cool is active) and calling for Heat, also the first relay switches the ASHP over from cooling to heating mode.  This prioritizes DHW pre-heat.

 

My ASHP is set to 45^oC for heating the buffer and 12^oC for cooling.  45^oC works well as I have a ΔT of 5C set so it takes it's time re-heating sitting at 34^oC whilst the PCM melts, usually finishing off at about 43^oC, currently it draws about 1.2kW (9kW split ASHP) for the majority for the time at it's most efficient CoP of >6, dropping to above 4 in winter.

[joth]

1 hour ago, jack said:

 

Exactly that.

 

To confirm, this means when switching from DHW to slab-cooling, and back again, it has to first "flush out" a supply-pipe length of hot water before the cold arrives (or vice-versa)? So if there's a long run from ASHP to the redirect valve, it will decrease the effective efficiency?  (e.g. pumping cold water through the UVC that it'll then have to heat back up again). 

 

Maybe this is negligible, and I'm probably overthinking this, but as I have a long run (aprx 20m) from ASHP to tank,  I'm currently thinking it would be better to have the redirect much nearer the ASHP and then send the cold water to the MVHR supply duct (which is off in a different direction to the tank anyway) so it will run in its own "dedicated" loop. 

Also, perhaps more importantly,  it just feels better to have cooling via air-ducts as that will get upstairs to the bedrooms, as the UFH slab is only downstairs. (with caveat there's only a limited amount of cooling you can do via air, but I'm not sure the slab is much more anyway as we don't want THAT cold a floor, for risk of condensation, right?)

 

[Jeremy Harris]

7 minutes ago, joth said:

 

To confirm, this means when switching from DHW to slab-cooling, and back again, it has to first "flush out" a supply-pipe length of hot water before the cold arrives (or vice-versa)? So if there's a long run from ASHP to the redirect valve, it will decrease the effective efficiency?  (e.g. pumping cold water through the UVC that it'll then have to heat back up again). 

 

Maybe this is negligible, and I'm probably overthinking this, but as I have a long run (aprx 20m) from ASHP to tank,  I'm currently thinking it would be better to have the redirect much nearer the ASHP and then send the cold water to the MVHR supply duct (which is off in a different direction to the tank anyway) so it will run in its own "dedicated" loop. 

Also, perhaps more importantly,  it just feels better to have cooling via air-ducts as that will get upstairs to the bedrooms, as the UFH slab is only downstairs. (with caveat there's only a limited amount of cooling you can do via air, but I'm not sure the slab is much more anyway as we don't want THAT cold a floor, for risk of condensation, right?)

 

 

 

The loss from flushing cold to hot through the supply pipes should be tiny.  If you had, say, two 10m runs of 22mm pipe from the ASHP, then the volume would be around 0.6l, so changing that volume of water from 10°C when cooling to 50°C when heating hot water would use about 0.028 kWh, so with a heat pump COP of 3, the energy used would be around 0.00933 kWh and the cost at 15p/kWh for electricity would be about 0.14p.  This ignores the fact that if the cooling was not running then the ASHP would still have to heat the water in these pipes from ambient temperature up to hot water temperature.

[jack]

49 minutes ago, joth said:

Also, perhaps more importantly,  it just feels better to have cooling via air-ducts as that will get upstairs to the bedrooms, as the UFH slab is only downstairs. (with caveat there's only a limited amount of cooling you can do via air, but I'm not sure the slab is much more anyway as we don't want THAT cold a floor, for risk of condensation, right?)

 

Why not do (or at least allow for) both? 

 

We have slab-cooling and it's remarkably effective at keeping the house cool. It definitely doesn't cool upstairs sufficiently, and I'd love the option of air cooling as well. I may try and retrofit at some stage - it would've been far easier if I'd planned it from the start.

 

Another possibility is fan-assisted radiators that cool as well as heat. They seem extremely expensive, but just for bedrooms they might be worth the cost.

[jfb]

by what method can the cold water produced by the ASHP cool the air supply of the MVHR?

[le-cerveau]

18 minutes ago, jfb said:

by what method can the cold water produced by the ASHP cool the air supply of the MVHR?

 

By utilizing a Duct cooler example: https://www.bpcventilation.com/cold-water-duct-cooler-range .

It will only have a limited effect though due to the relatively low air volume movement.

[Jeremy Harris]

16 minutes ago, jfb said:

by what method can the cold water produced by the ASHP cool the air supply of the MVHR?

 

You could fit a duct cooler to do this.  However, our experience of running an MVHR with a built in air cooling function from its own integral air-to-air heat pump has been that it's not very powerful.  It will reduce the temperature a small amount, but it's not as effective as cooling the slab when it comes to keeping the house cool.  I'll admit to being surprised at just how effective slab cooling is, as when I first did it I wasn't expecting it to be as good as it is.

 

I think that fitting a separate fan cooling unit, with the core supplied by chilled water from the ASHP, might be more effective than fitting a duct cooler to the MVHR, just because a fan cooling unit will shift a lot more air, and would work with recirculated room air, which in hot weather would probably improve performance a fair bit.

[jack]

4 hours ago, le-cerveau said:

By utilizing a Duct cooler example: https://www.bpcventilation.com/cold-water-duct-cooler-range .

It will only have a limited effect though due to the relatively low air volume movement.

 

My suspicion is that it doesn't need to have a lot of effect if it's being used in conjunction with floor cooling downstairs.

 

We have a lot of PV. The aim would be that during hot weather, the cooling is on permanently from as soon as the sun is up when you know it's going to be a hot day. It should cost little to nothing to run, because when the sun's out on a cloudless day, we're generating a lot of surplus energy most of the time.

 

My experience living in hot climates is that it's easier to keep the environment cool if it's prevented from getting too hot in the first place. Even being able to reduce the peak temperature by 2-3 degrees across the day would be very helpful - big difference trying to sleep at 23 deg C versus 26 deg C!

 

4 hours ago, JSHarris said:

I think that fitting a separate fan cooling unit, with the core supplied by chilled water from the ASHP, might be more effective than fitting a duct cooler to the MVHR, just because a fan cooling unit will shift a lot more air, and would work with recirculated room air, which in hot weather would probably improve performance a fair bit.

 

Interesting idea. The main issue is where to put it!

[Adam2]

4 hours ago, JSHarris said:

I think that fitting a separate fan cooling unit, with the core supplied by chilled water from the ASHP, might be more effective than fitting a duct cooler to the MVHR, just because a fan cooling unit will shift a lot more air, and would work with recirculated room air, which in hot weather would probably improve performance a fair bit.

 

Do you mind explaining what this would entail? Is this like the duct cooler (as per link to BPC) but using an independent distribution duct system and an in-line fan to get a decent airflow?

[ProDave]

A fan cooling unit, also known as a fan coil unit, is the bit you are probably all familliar with in an office air conditioning system.  It takes many forms, wall or ceiling mounted.

 

Pass cool air ( fluid ? ) through the coil and the fan sucks in room air and passes it back out again a bit cooler.

 

Here is an example of some, not a recommendation, just the first picture of different sorts I could find  https://www.aermec.co.uk/portfolio/fan-coil-units/

 

You would typically have one in each main room and the heat pump can feed (within  it's capacity) any number of them.

Edited May 26, 2019 by Nickfromwales

[Jeremy Harris]

36 minutes ago, jack said:

Interesting idea. The main issue is where to put it!

 

That is something I've been pondering over for a couple of years!  Best place I can think of is high up in our entrance lobby, as with a lot of faffing around I think I might be able to fiddle a couple of pipes, plus a drain line, down behind the 50 x 50 battens that form the service void (unfortunately the service void battens run the wrong way...).

 

17 minutes ago, Adam2 said:

 

Do you mind explaining what this would entail? Is this like the duct cooler (as per link to BPC) but using an independent distribution duct system and an in-line fan to get a decent airflow?

 

It would look like an aircon indoor unit, but fed with chilled water.  Chilled water coolers tend to be used in big offices, as they avoid having to run refrigerant lines all around the place.  We had them in the last place I worked, but passive ones (no fan) that were just big flat plates in the ceiling with chilled water fed through them, like radiators mounted on their sides.

[Ed Davies]

48 minutes ago, ProDave said:

Pass cool air through the coil

 

Water?

[joth]

7 hours ago, jack said:

 

Why not do (or at least allow for) both? 

 

We have slab-cooling and it's remarkably effective at keeping the house cool. It definitely doesn't cool upstairs sufficiently, and I'd love the option of air cooling as well. I may try and retrofit at some stage - it would've been far easier if I'd planned it from the start.

 

Another possibility is fan-assisted radiators that cool as well as heat. They seem extremely expensive, but just for bedrooms they might be worth the cost.

 

<insert "why not both" meme here>

 

Yes, indeed. My spec currently calls for a mid-position value to redirect between UFH and MVHR duct cooling. The thing that concerned me is the complexity of dialing in their respective target cooling temperature if it's driving both at once.  I'm doing all the cooling on the basis of  "run the pipes now, figure out commissioning it later" 

 

 

 

Edited May 23, 2019 by joth

[ProDave]

1 minute ago, joth said:

 

<insert "why not both" meme here>

 

Yes, indeed. My spec currently calls for a mid-position value to redirect between UFH and MVHR duct cooling. The thing that concerned me is the complexity of dialing in their respective target cooling temperature if it's driving both at once.  I'm doing all the cooling on the basis of  "run the pipes now, figure out commissioning it later" 

 

 

 

It won't be driving both at once.

 

In this set up, it will either be heating DHW, heating the house (e.g ufh) or cooling the house (e.g fan coil unit)

 

It will only do one at a time, under the control of the heat pumps controller. and suitable valves will direct the water (hot or cold) to the correct destination.

[Stones]

10 hours ago, jfb said:

is it as simple as switching over from heating to cooling at different times (presumably with dhw taking precedent)?

 

Yes.  Accessing the cooling function will differ from manufacturer to manufacturer.  In our case (Mitsubishi Ecodan), flipping a dip switch in the control box enables the cooling control function.

[joth]

13 minutes ago, ProDave said:

It won't be driving both at once.

 

 

Maybe the context there was lost on this point, but by doing "both at once"  i meant cooling via slab and cooling via ventilation duct at the same time.   It seems physically plausible to cool both at once, but questionable if it's worth the complexity. 

 

[Jeremy Harris]

4 minutes ago, joth said:

 

Maybe the context there was lost on this point, but by doing "both at once"  i meant cooling via slab and cooling via ventilation duct at the same time.   It seems physically plausible to cool both at once, but questionable if it's worth the complexity. 

 

 

 

Easy enough to do, and probably worth doing.  Air cooling feels better, in that the effect is felt pretty soon after it comes on, whereas the slab cooling takes an hour or two to have any noticeable effect.

[Stones]

Perfectly doable, and something I seriously considered - all your doing in effect is adding another loop to the circuit.  I decided it wasn't worth the bother given the size of duct cooler that would be needed to make any meaningful difference to the temp of the incoming air.

[Dreadnaught]

I like the idea of an extra loop for duct cooling/heating. I think it gives the flexibility for duct cooling but also heating too.

 

As @jack said: "If I were doing it again, I'd stick with UFH driven by an ASHP, but add a loop to allow some comfort heating of the MVHR supply air (really just enough to take the chill off the air due to the imperfect heat exchange in the MVHR unit)." 

 

https://forum.buildhub.org.uk/topic/7859-top-up-heat-sources/?do=findComment&comment=133325

 

One thing to consider, with a duct cooler you might need a condensate drain, unless the amount of condensation is so low that it can be allowed to evaporate.

Edited May 23, 2019 by Dreadnaught

[Jeremy Harris]

20 minutes ago, Dreadnaught said:

One thing to consider, with a duct cooler you might need a condensate drain, unless the amount of condensation is so low that it can be allowed to evaporate.

 

You definitely will need a condensate drain.  Our experience with the Genvex is that there is a constant trickle of condensate from the drain when it's in cooling mode.

[ProDave]

1 hour ago, joth said:

 

Maybe the context there was lost on this point, but by doing "both at once"  i meant cooling via slab and cooling via ventilation duct at the same time.   It seems physically plausible to cool both at once, but questionable if it's worth the complexity. 

 

That would be easy to do on mine.  When you select cooling mode it turns on output that it expects to power a changeover valve to switch from the UFH to the FCU.  If instead you used that to power a 2 port valve that just enabled flow to the FCU as well as the UFH you would have what you want.

[ragg987]

I think cooling via mvhr will require a lower flow temperature than cooling via slab. So I am not convinced doing both at once makes a lot of sense. To get meaningful coolth via mvhr is going to need a large delta temperature as air flows are relatively low.

[Jeremy Harris]

Our MVHR cools at around 10 to 12 deg C at the heat exchanger, which is about the same as the flow temperature I run through the floor.  The floor surface never gets down to the flow temperature; it seems to sit around 5 or 6 deg C above it, usually around 16 to 18 deg C. 

 

Based on that, I'd say that a duct cooler run from our ASHP would probably work as well as the built in air-to-air pump does.  The main snag with using the MVHR is the relatively low air flow rate, though.

[willbish]

Would large volumes of air recirculating through fan cooling units cause any upset to the MVHR unit?

[Jeremy Harris]

43 minutes ago, willbish said:

Would large volumes of air recirculating through fan cooling units cause any upset to the MVHR unit?

 

 

Shouldn't have any effect on the MVHR, as there would be no net change in the MVHR operating conditions. 

 

I quite like the idea of recirculating air for cooling, as it should be pretty efficient, a bit like the way setting a car heating/cooling system to recirculate tends to make it perform a bit better.