Prepping for ASHP and sizing - Heat loss calcs confusion

[saveasteading]

I've looked in detail at the standalone sircon units that are very common in Spain. In the diy stores they will have about 20 models.

I box outside,  pipes through the wall and a raduator/ fan inside. They are optimised for cooling but will also act as heaters, but not very efficiently....better than an electric heater but not much.

It seems that the heat pumps are designed that way ie for heating or cooling most efficiently.

I suppose the big difference is that in UK we are heating up to 20 when it might be zero outdoors all day, whereas  in southern Spain in summer  it will be cooling  down to 25 when it is 35-40 at mid afternoon, dropping to 20 at night.  ISH.... my new SI term to indicate very wild approximations.

 

I wonder what the Spanish and French do in areas where they get very hot summers and also  cold winters. Perhaps their units are optimised to heat and to cool.

[SimonD]

2 hours ago, jack said:

I can only talk about my personal experience, but we cool our downstairs slab with an ASHP during hot periods and it's remarkably effective. Coming in from outside on a hot day is like walking into a cool cave. We run a flow temp of about 16 °C and that's enough to keep the slab under about 20 °C, even in a multi-day heat wave.

 

We do have concrete floors, which I'm sure helps a lot. I don't imagine the effect would be as powerful with, e.g., wooden floors.

 

Yes, the concrete floors will help a lot, but I'd be curious to know how the floor temps are when the ASHP is not running? Have you taken any comparative measurements? 

 

What we ideally need are specific figures to understand the W/m2 can be gained from a floor during cooling

[jack]

1 hour ago, SimonD said:

Yes, the concrete floors will help a lot, but I'd be curious to know how the floor temps are when the ASHP is not running? Have you taken any comparative measurements? 

 

What we ideally need are specific figures to understand the W/m2 can be gained from a floor during cooling

 

I only started running Grafana earlier this year, so the only data I currently have are Loxone native (and hence probably not much help).

 

For context, I presently run the cooling open loop. I can enable cheap rate cooling and/or daytime cooling (scheduled between 10:00 and 16:00, from memory). I can also push a button and get 2, 4, 6, or 8 hours of cooling. Periods where the cooling doesn't come on for a period are usually cooler and/or cloudy (and hence less solar gain) periods.

 

This shows the downstairs slab temp (note: not air temp) and the UFH flow temp for June and July last year:

 

  

 

Note the runup to the peak slab temperature in late June. With the cooling off, the temperature rose consistently from 19.4 on Monday 23 June to 21.6 on Saturday 28 June, when I enabled cooling   

 

This is what the weather was doing during June 2025:

 

 

 

The house has a long time constant when it comes to reacting to external temperatures. Even though the temperature in June was highest on about 21 June and fell off sharply after that, the internal house temperature continued rising for a couple of days before I turned the cooling back on.

 

Unsurprisingly, the cooling downstairs has virtually no impact on upstairs temperatures. Here's 10 days starting on 23 June, showing the relentless increase in upstairs temperature even after the cooling is turned on downstairs on the Saturday:

 

 

That was actually the hottest it got upstairs in all of 2025.

 

Not sure if any of that helps. I originally planned to add things like flow sensors along with power monitoring for the ASHP so I could get a better sense of what was going on an perhaps tweak things for better performance and lower costs, but in the end I decided it was too expensive and complex. That said, earlier this year I expanded the inputs available for Loxone, such as excess solar power and temperature forecasts. I'm hoping to do something with those to better automate cooling this year.

 

    

[mistake_not]

1 hour ago, SimonD said:

What we ideally need are specific figures to understand the W/m2 can be gained from a floor during cooling

Wait x months* and I'll have some data...

 

*Where months may be years....

[JohnMo]

4 hours ago, jack said:

which I'm sure helps a lot. I don't imagine the effect would be as powerful with, e.g., wooden floors.

We are mostly oak on top of concrete, and the effect of cooling is pretty good.

4 hours ago, jack said:

Coming in from outside on a hot day is like walking into a cool cave

Good analogy

 

We had two similar days one pre cooling and the next with cooling. Cooling knocked around 3 degs off absolute max temperature, but more importantly, once solar gain stopped, house recovered to more normal temperature way quicker. 

 

I look at cooling as a freeby of having a heat pump installed. We get what we want, at zero install cost, is it Aircon - no, do you need Aircon maybe not. Having lived with Aircon for a few years (overseas), not sure I want the endless air blast either. UFH heat and cool, is an easy to live with option. In absolute terms the cooling isn't designed, we accept what it provides in comfort a bonus. Our cooling will be stitched on next week and stay on until around October.

[JohnMo]

23 minutes ago, jack said:

I'm hoping to do something with those to better automate cooling this year

Last year I automated mine via flow temp set point and stop start hysterisis, and ran circulation pump 24/7. Ran on a pure demand cycle.

 

New heat pump won't be run that way, as 8 don't have the freedom change some of the parameters, now will have a room sensor doing the automation, so I get cooling whenever I need it, heat pump run on fixed flow temperature 

[-rick-]

4 hours ago, SimonD said:

Add to this that heat pumps are designed and developed primarily for heating and you have a system that can do something else - a little bit of cooling, but it's questionable how much it's been developed and tested for this.

 

Maybe this is true for UK specific monobloc, but heatpumps were primarly invented for cooling. The vast vast majority of heatpumps deployed worldwide do cooling first, heating second. Including air to water ones. Reversible heatpumps have been available for decades globally though only more recently in a mass market form. Once you have a working and efficient heatpump the engineering required for the reversing valve is almost trival.

 

In any case, I think your above statement is not justifiable for any heatpump that was not designed specifically for the UK market.

[JohnMo]

9 minutes ago, -rick- said:

deployed worldwide do cooling first, heating second. Including air to water ones. Reversible heatpumps have been available for decades globally though only more recently in a mass market form. Once you have a working and efficient heatpump the engineering required for the reversing valve is almost trival.

To support the above.  An a2w heat pump is really a2a with a water heat exchanger added instead of a house internal fan coil. Cooling is a pretty simple concept for the actual heat pump, heating is quite complex, as you need to accommodate defrosting, hence the addition of the 4 way valve.  ALL heating ASHP can do cooling, as they all have a functioning 4 way valve. Many manufacturers deploy ASHP without cooling controls or add the controls as an option extra.

 

Interesting fact, my Hiaer heat pump comes with cooling out the box, but add a smart optimization system, cooling becomes no longer available - go figure.

Edited 6 hours ago by JohnMo

[-rick-]

8 minutes ago, JohnMo said:

Cooling is a pretty simple concept for the actual heat pump, heating is quite complex, as you need to accommodate defrosting, hence the addition of the 4 way valve.  ALL heating ASHP can do cooling, as they all have a functioning 4 way valve.

 

Purely a guess but I suspect this isn't entirely true. True of anything on the market today, likely not going back a few years. Can imagine some early, non-inverter types having some form of resistance electric defrost.

[JohnMo]

7 minutes ago, -rick- said:

 

Purely a guess but I suspect this isn't entirely true. True of anything on the market today, likely not going back a few years. Can imagine some early, non-inverter types having some form of resistance electric defrost.

Article from 2012 discusses how a 4 way valve is used on a heat pump 

https://www.danfoss.com/en/service-and-support/case-stories/dcs/components-for-heat-pumps-part-5-four-way-reversing-valves/

 

Carrier started using them in production models in the 1970/80s. So for all purposes of this discussion, 4 way valves have been about for ever.

Edited 6 hours ago by JohnMo

[-rick-]

1 minute ago, JohnMo said:

Article from 2012 discusses how a 4 way valve is used on a heat pump 

https://www.danfoss.com/en/service-and-support/case-stories/dcs/components-for-heat-pumps-part-5-four-way-reversing-valves/

 

Carrier started using them in production models in the 1970/80s. So for all purposes of this discussion been about for ever.

 

Has been a possibility != every heatpump uses this as the solution. Reversing valves were at one point one of the more expensive components in the system so I'm guessing that in the past some manufacturers cheaped out and used alternative means for defrost.

[jack]

1 hour ago, JohnMo said:

Having lived with Aircon for a few years (overseas), not sure I want the endless air blast either. 

 

I spent many years working air-conditioned offices in Australia. The dry air and cold drafts aren't something I found very pleasant.

 

By contrast, underfloor cooling feels very natural.

[JohnMo]

5 minutes ago, -rick- said:

 

Has been a possibility != every heatpump uses this as the solution. Reversing valves were at one point one of the more expensive components in the system so I'm guessing that in the past some manufacturers cheaped out and used alternative means for defrost.

Who knows, still not really relevant to heat pumps currently being installed or installed in the last decade or more, they all had/have 4 way valves. If someone has a historic ASHP, that doesn't do refrigerant defrosts, good luck to them.

[JohnMo]

5 minutes ago, jack said:

dry air and cold drafts aren't something I found very pleasant

We got used to switching off the Aircon at bedtime and opening the windows and letting the 32 Deg near 100% humidity in (Singapore), better than the cold draft and head ache it caused.

 

Extremely good (expensive) does get around this slightly, by adding humidity to the airflow and better control of airflow direction, but nothing I would invest in.

Edited 6 hours ago by JohnMo

[SimonD]

32 minutes ago, -rick- said:

 

Maybe this is true for UK specific monobloc, but heatpumps were primarly invented for cooling. The vast vast majority of heatpumps deployed worldwide do cooling first, heating second. Including air to water ones. Reversible heatpumps have been available for decades globally though only more recently in a mass market form. Once you have a working and efficient heatpump the engineering required for the reversing valve is almost trival.

 

In any case, I think your above statement is not justifiable for any heatpump that was not designed specifically for the UK market.

 

My comments are absolutely justifiable in the context of this discussion. The discussion was about heat pumps that are designed for heating, not heat pumps that are designed for cooling. Yes, they're both heat pumps in so far as they move heat from one place to another, but a heat pump does not function in and of itself without a wider system that is designed either for heating, or for cooling, or as we've seen recently heating with some cooling capacity. This is where the conversation started:
 

22 hours ago, JohnMo said:

But not all will do cooling if you need that. Example, current Grant heat pumps physically will do cooling BUT their controller does not allow this happen. Most installers are clueless about cooling, so be prepared for plenty of BS.

Then @saveasteading asked a question about cooling to which I answered:

21 hours ago, SimonD said:

 

You're not far off. Cooling effectiveness of ASHP isn't that great, you may get a few degrees drop during the hottest days, so it might take the house from uncomfortably hot to okay, but that's about it. If you're in a position where you need to drop time, money and resources on infrastructure for an ASHP to do cooling, you're better of just getting a split a/c unit. I made that choice.

 

Here, you can clearly see that I'm actually using a distinction between an ASHP (implied for heating) versus a split a/c unit (which is also a heat pump), in the hope that it would help to clarify the difference, but clearly not. However, despite going round the houses, @JohnMo then confirms exactly what I said:

 

1 hour ago, JohnMo said:

We had two similar days one pre cooling and the next with cooling. Cooling knocked around 3 degs off absolute max temperature, but more importantly, once solar gain stopped, house recovered to more normal temperature way quicker. 

 

I look at cooling as a freeby of having a heat pump installed. We get what we want, at zero install cost, is it Aircon - no, do you need Aircon maybe not. Having lived with Aircon for a few years (overseas), not sure I want the endless air blast either. UFH heat and cool, is an easy to live with option. In absolute terms the cooling isn't designed, we accept what it provides in comfort a bonus. Our cooling will be stitched on next week and stay on until around October.

 

As for reversing valves, yes they exist and they're used in ASHP designed for heating, but often the reversing valves have slightly different designs for the purposes of either mainly heating or mainly cooling, and they have different control strategies. So the fact that an ASHP heat pump for heating can reverse cycle, doesn't mean it's going to be great at cooling, or that it can do cooling at all. (and then approach to the design of controls is yet another matter where there are differences between 'cooling' and 'heating' based manufacturers in how they implement heating controls)

 

But beyond this, the cooling effectiveness, as I've clarified above, of a heat pump for heating, is dependent upon the design of the whole system, not just the unit. And a system designed for heating has multiple drawbacks when it comes to reversing the flow of heat, due to a number of factors. Hence why what we're seeing here is exactly what I said - a reduction of a few degrees that increases comfort, but if you're in a position where adding cooling requires a huge amount of investment in infrastructure etc. to make your heating heat pump cool, you're better off installing a multi-split, which is of course is a heat pump, but it's a system designed to do a different thing mainly and would be far cheaper. 😉😏

But like I also said, fundamentally, you're probably better off designing passive cooling strategies into a house at the design stage....than relying on the heat pump, except for in exceptional circumstances.

 

[JohnMo]

1 hour ago, SimonD said:

However, despite going round the houses, @JohnMo then confirms exactly what I said

Sorry for applying real life experience of cooling v your theory. Room temp down 3 degs is huge for comfort, plus the actual house temp feels way cooler than that, as @jack says more like going into a cave.

 

Passive design is best, but I actually prefer the views, so some active cooling is needed, plenty of solar pays the bills.

[SimonD]

2 minutes ago, JohnMo said:

Sorry for applying real life experience of cooling v your theory. Room temp down 3 degs is huge for comfort, plus the actual house temp feels way cooler than that, as @jack says more like going into a cave.

 

This just gets weirder and weirder, as it seems you're trying to prove a pointless point, so probably not even worth engaging in further discussion. However..

 

Sorry for confirming what I said?

 

So in @jack's case, I can presume that the UFH works well to keep the upstairs warm in winter, but from the charts, shows it has no effect on upstairs for cooling and as he says 'unsurprisingly.' This demonstrates it isn't a whole house cooling strategy, even if it does provide comfort downstairs. Forgive me if I'm wrong @jack?

 

Like I think I've said a couple of times in this thread, cooling is difficult to define, and must be defined and quantified as well as it can be so everyone is on the same page. It's fundamentals like cooling what (how big), by how much, for how long, etc. that need to be determined, understood and agreed at the outset, even in a short conversation like this. And then being explicit about the system parameters used to achieve the aims.

In your instance for example, we don't know what kind of heat input your system is dealing with when you make your claims, is outdoor temperature at 21, 23, 29, or even 32C, what are the heat gains such as through windows or elsewhere. What temperature are you seeking indoors? When does your house actually start needing the active cooling input for your comfort? What actual kW heat transfer is your system able to deal with during cooling? What time periods are you running? I think cooling design is just as much of a heat loss & design task as heating. Which is why I asked for data, as on the data, I'm very happy to change my views, which are not based on 'my' theory but standards, calculations, and some knowledge from the wider industry. 
 

11 minutes ago, JohnMo said:

Passive design is best, but I actually prefer the views, so some active cooling is needed, plenty of solar pays the bills.

 

Views and passive cooling are not mutually exclusive, and my comments about passive cooling are not a criticism of your design decisions. I add in my comments about this as I hope it helps self-builders in the early stages consider heat gain and how to deal with it in the early phase as there have been plenty of threads over the years where this has caught people out, and following completion have struggled with over-heating.

[SimonD]

4 hours ago, jack said:

I only started running Grafana earlier this year, so the only data I currently have are Loxone native (and hence probably not much help).

 

It's a shame there isn't more granularity, but definitely interesting to look at the behaviour of the system and charts.

[JohnMo]

1 hour ago, SimonD said:

This just gets weirder and weirder, as it seems you're trying to prove a pointless point

You're obviously had a bad day and need to get your own way.

[SimonD]

3 minutes ago, JohnMo said:

You're obviously had a bad day and need to get your own way.

 

Why are you trying so hard to make the discussion so unpleasant and personal John? All I've done is quoted what you've said and reasonably replied and questioned it, and asked you for some data. It's just very curious.

[mistake_not]

So, now that lovely discussion is out the way. Anyone got recommendations for a 5kw pump that does heating and cooling? Obvious candidates are Viessman and Valiant but I know nother about HP manufacturers really.

 

Only requirements other than heating and cooling is integrated into Home assistant so I can keep the cooling point above the dew point, and (probably separately) do weather comp for heating. 

 

Plan is a simple open system, no zoning, have enough water volume to not need a buffer, and have bug enough pipework for dt5 flow rates.

Edited 2 hours ago by mistake_not
Wrong place full stop

[JohnMo]

20 minutes ago, mistake_not said:

Valiant

Be careful as it doesn't do cooling out the box, without a widget being added.

 

22 minutes ago, mistake_not said:

integrated into Home assistant so I can keep the cooling point above the dew point

Most will take a zero volt switch permissive to ask for heat/cool. If you want to do dew point control, plenty of simple thermostats will do do control for cooling, a Computherm Q20RF has everything built in for £65.

[mistake_not]

32 minutes ago, JohnMo said:

Be careful as it doesn't do cooling out the box, without a widget being added.

Yeah, seems like a 10p resistor they charge £300 😬

[SimonD]

44 minutes ago, mistake_not said:

Obvious candidates are Viessman and Valiant but I know nother about HP manufacturers really.

 

It really depends on your budget. Stiebel Eltron, and Nibe both do heating and cooling and are very nice units. Viessmann currently requires an indoor unit, but also very nice and some of the best controls in the business. My Viessmann rep told me there is a monobloc coming, probably in the Autumn. Panasonic also do some nice units with cooling and these can be paired with their fan coils. And as you've listed, Vaillant. I think Vaillant is probably the cheapest on this list, but there may be a Panasonic about the same price. Most people like and choose Vaillant because of the standards of support available. Daikin also do cooling but I don't know much about them as I'm not an installer for Daikin and haven't had their training.