Upstairs - UFH, AC or Fan coils?

[JohnMo]

UFH throughout (single storey) does heat and cool.  Cooling isn't the be all, end all of cooling, but with none of the blowing air of Aircon (which I started to hate after living in Asia). But does make house more comfortable for zero additional equipment and zero costs, house doesn't have the extreme of heat and cools down before bed time.  But we have huge amounts of solar gain, once outside is as cool or cooler than inside we purge ventilate as well.

[Dave Jones]

13 hours ago, flanagaj said:

I’m dragging this post back up as I’m keen to get people’s thoughts on their decisions given the amazing hot summer we are having.  Whose house has remained nice and cool.  Be honest now!

 

photo below taken when it was 35.2C outside according to my weather station, ASHP running at 16C (dew point was around same) bedrooms remained at 21C during peak heat dropping to 19C once dark and the fan coils clicked off.

 

Would never be without them again.

 

[SBMS]

1 hour ago, Dave Jones said:

 

photo below taken when it was 35.2C outside according to my weather station, ASHP running at 16C (dew point was around same) bedrooms remained at 21C during peak heat dropping to 19C once dark and the fan coils clicked off.

 

Would never be without them again.

 

What units you got there @Dave Jones?

[JohnMo]

Only thing to add about fan coils is the heat pump NEEDS to be sized correctly, if it's too big the heat pump will cycle, sized correctly with decent modulation, iit will just tick away all day. The fan coil will switch on off in response to heat pump cycling. We have that issue with the summer house and our oversized with limited modulation heat pump, so we end up getting a 2 deg swing in temperature, on all but the hottest days. Once we get to 30 heat pump will run for several hours at a time.

[Thorfun]

16 hours ago, flanagaj said:

I’m dragging this post back up as I’m keen to get people’s thoughts on their decisions given the amazing hot summer we are having.  Whose house has remained nice and cool.  Be honest now!

our house is cool but that's because we have the AC on! 🤣

we knew we'd want AC for the bedrooms as even with external shading things just warm up quickly and so the AC keeps us at our desired set temperature. we didn't put heating upstairs apart from electric towel radiators and ufh in the bathrooms safe in the knowledge that if we ever did need supplementary heating upstairs then the AC would do that.

[Thorfun]

13 hours ago, flanagaj said:

That sounds bliss.  Our Persimmon 3 storey rental was 29.5c in the top bedroom 🥵 that's why I'm currently all over designing a decent solution for our build

there's only one solution......air conditioning. 😉 

[Dave Jones]

54 minutes ago, SBMS said:

What units you got there @Dave Jones?

 

panasonic smart

[JohnMo]

Or an alternative to UFH and fan coils 

 

https://www.variotherm.com/en/products/modular-wall-heatingcooling/technical-information.html

[SBMS]

Continuously second guess as to whether to go fancoils and ASHP in reverse or true AC. Would be much more cost effective with FCUs and ASHP in reverse, but have concerns that it won't cool house sufficiently (how to calculate the ground floor cooling capacity??) and how hot water generation can happen at same time? I hear lots of people talking about manually setting jumpers on heat pumps to run in reverse, lagging of pipes for condensate etc. Sounds difficult to do as a whole house system.  That, and the peak cooling load for our house (worst worst case) is circa 24kW. I don't even know what the 'cooling capacity' of a 12kW heat pump actually is (is it the same?? 12kW??)

[joth]

@SBMS 24kW cooling load?? If you're serious about meeting that, forget underfloor cooling and water heat pump, it won't delivery that. Talk to a commercial refrigeration expert 

 

Specifically: a 12kW heat pump will typically have a bit lower nominal cooling capacity (depends on model), but will have much much lower practical capacity unless you run it at around 5°C, with all the heavy condensation issues that brings up.

UFH can't safely be run below 12°C minimum, and even then has lower effective emitter power in cooling than heating due to lack of convection currents.

So I'd guess you'd get 4-6kW max effective cooling. 

 

At best you can run some modest cooling from the ashp in addition to an industrial sized A/C system to help support it. 

Good luck. 

[SBMS]

3 minutes ago, joth said:

@SBMS 24kW cooling load?? If you're serious about meeting that, forget underfloor cooling and water heat pump, it won't delivery that. Talk to a commercial refrigeration expert 

 

Specifically: a 12kW heat pump will typically have a bit lower nominal cooling capacity (depends on model), but will have much much lower practical capacity unless you run it at around 5°C, with all the heavy condensation issues that brings up.

UFH can't safely be run below 12°C minimum, and even then has lower effective emitter power in cooling than heating due to lack of convection currents.

So I'd guess you'd get 4-6kW max effective cooling. 

 

At best you can run some modest cooling from the ashp in addition to an industrial sized A/C system to help support it. 

Good luck. 

Just to be clear that is Peak Cooling Load (the maximum instantaneous cooling demand).  As I understand it, most HVAC designers will size equipment based off the peak load.  I used these figures when calculating the peak vs the average for solar gain, temperature delta etc. 

 

Component	Peak Value	Average Value	Ratio
Solar Gain	600–800 W/m²	300–400 W/m²	~2×
ΔT (cooling)	9°C	~5–6°C	~1.5×
Internal Gains	Max occupancy	50–75% occupancy	~0.5–0.75×
Total Load	100%	50–70%	~0.6× typical

 

My Average Cooling Load is much lower, around 9kW in the summer.

[JohnMo]

29 minutes ago, SBMS said:

That, and the peak cooling load for our house (worst worst case) is circa 24kW.

Sorry s bit of a rant below.

 

Cannot believe that. Our lounge is 6m tall, one end is fully glazed, to make it worse it's a bay window, even with roof overhang gets full sun from around 4pm, we control the heat with internal blinds and UFH at 300mm centres, so not even ideal for cooling. Our typical temperature trend for the lounge is below. Gets to 24.5 degs, but feels cooler due to cool floor sucking your heat away. And temp drops pretty quickly. In total we have around 50m² of glass facing south west on the front elevation of the house. A 6kW ASHP pulls about 4.5kW max.

 

 

 

5 minutes ago, SBMS said:

My Average Cooling Load is much lower, around 9kW in the summer.

But that is not real. You have zero need to size for peak load or the way the average is done, or close to it in a house. We get peak load for a few hours per day. The other day 30 degs outside and no cloud, floor pulled 50 kWh from inside house, so an average of near 2kW.  According to your calcs I need nearer 50kW cooling input - that's just bonkers.

 

You only get solar gain when sun is actually on the window and could or should only be a a few hours per day. You will have curtains or blinds (internal or external) these slash the heat gain numbers.  People aren't in the room all the time. A floor a couple of degrees cooler than the air will pull a huge amount of energy out of a room. When we are at 24 degrees we have a room air to floor delta of 6 degs over 38m². 

 

You need to take a series of average heat gains and then make an average of that, then you just trickle the cooling in 24/7. What is important here is comfort, not the actual temperature.

[ProDave]

19 hours ago, flanagaj said:

I’m dragging this post back up as I’m keen to get people’s thoughts on their decisions given the amazing hot summer we are having.  Whose house has remained nice and cool.  Be honest now!

We only had 2 extremely hot days so far at 31 degrees and keep windows and curtains shut in the day and open windows for night purge has worked well without needing to persuade the ASHP to run in cooling mode  (only have UFH so it is not that good at cooling)

[SBMS]

2 minutes ago, JohnMo said:

Sorry s bit of a rant below.

 

Cannot believe that. Our lounge is 6m tall, one end is fully glazed, to make it worse it's a bay window, even with roof overhang gets full sun from around 4pm, we control the heat with internal blinds and UFH at 300mm centres, so not even ideal for cooling. Our typical temperature trend for the lounge is below. Gets to 24.5 degs, but feels cooler due to cool floor sucking your heat away. And temp drops pretty quickly. In total we have around 50m² of glass facing south west on the front elevation of the house. A 6kW ASHP pulls about 4.5kW max.

 

 

 

But that is not real. You have zero need to size for peak load or the way the average is done, or close to it in a house. We get peak load for a few hours per day. The other day 30 degs outside and no cloud, floor pulled 50 kWh from inside house, so an average of near 2kW.  According to your calcs I need nearer 50kW cooling input - that's just bonkers.

 

You only get solar gain when sun is actually on the window and could or should only be a a few hours per day. You will have curtains or blinds (internal or external) these slash the heat gain numbers.  People aren't in the room all the time. A floor a couple of degrees cooler than the air will pull a huge amount of energy out of a room. When we are at 24 degrees we have a room air to floor delta of 6 degs over 38m². 

 

You need to take a series of average heat gains and then make an average of that, then you just trickle the cooling in 24/7. What is important here is comfort, not the actual temperature.

I don’t disagree with your logic @JohnMo and probably the average is even lower. I think the AC units have the ability to modulate pretty low so oversizing isn’t a massive deal and the price difference between say a 15kW or 25kW unit is pretty marginal. So does it hugely matter if I have a system larger than is needed most of the time? Appreciate it’s different with ASHP sizing and that’s important to get right. 
 

It might be different in the world of AC but all suppliers I’ve spoken to size to peak cooling load.

 

fyi lots of south facing glass

[JohnMo]

8 minutes ago, SBMS said:

oversizing isn’t a massive deal and the price difference between say a 15kW or 25kW unit is pretty marginal.

Except you get into the realms of applying for dno permission at that size of unit, your cables all get bigger etc. start up current gets bigger. 

 

16 minutes ago, ProDave said:

only have UFH so it is not that good at cooling

You would be surprised how different it makes the house feel.

 

9 minutes ago, SBMS said:

Appreciate it’s different with ASHP sizing and that’s important to get right. 

It's important equally for A2A. 

 

A2A is a different cooling mechanism, as air holds very little energy and next to no inertia. Sizing for peak means you can control room temperature with precision, but do you really need too?

[Thorfun]

1 hour ago, SBMS said:

I hear lots of people talking about manually setting jumpers on heat pumps to run in reverse, lagging of pipes for condensate etc. Sounds difficult to do as a whole house system.  That, and the peak cooling load for our house (worst worst case) is circa 24kW. I don't even know what the 'cooling capacity' of a 12kW heat pump actually is (is it the same?? 12kW??)

this all equals faff!

 

it's why i ditched the idea and just went separate AC. 

[SBMS]

10 minutes ago, Thorfun said:

this all equals faff!

 

it's why i ditched the idea and just went separate AC. 

What did you put in?

[Beau]

We have two properties here. A barn I converted around 18 years ago which was insulated above regs of the time (below now) and a farmhouse thats work in progress. The farmhouse has no floor insulation and I'm yet to do the lofts. All it has is EWI of 90mm (EPS) on the old 600mm thick stone walls and it has not got above 22C downstairs throughout even though its peeked at 31C outside. The barn on the other hand has sat in the mid to high 20s through the hot spell.

 

It's been surprising to me how well the modestly insulated mass of the farmhouse has avoided overheating. It wasn't even bad to heat last winter! Looking forward to how much better it will be when the lofts are insulated

[Thorfun]

12 minutes ago, SBMS said:

What did you put in?

Mitsubishi AC unit. i got a local company in to design and install it to the budget we had. as the budget wasn't limitless we had to compromise and have one ducted unit cooling both kids bedrooms which is a bit of a pain if one kid wants their room cooler than the other. but such is life.

[JohnMo]

3 minutes ago, Beau said:

It's been surprising to me how well the modestly insulated mass of the farmhouse has avoided overheating

Assume get very little solar gain through windows?

[SBMS]

How would one go about calculating the cooling output of the slab running in reverse? Say I have a room that is 11sqm with a cooling requirement of 700 watts... How could I calculate if the slab could cool that space?

[Beau]

42 minutes ago, JohnMo said:

Assume get very little solar gain through windows?

Never measured the glazing area but yes I suspect so. 

[JohnMo]

2 hours ago, SBMS said:

How would one go about calculating the cooling output of the slab running in reverse? Say I have a room that is 11sqm with a cooling requirement of 700 watts... How could I calculate if the slab could cool that space?

The output of cooling is just the inverse of heating 

 

In simple terms if the room is 24, the floor would need to power of 63W/m² (700W /11m²), so floor temp of 24-6 (from chart below), so 18 degs floor surface temperature. As room temp gets closer to room temp output reduces eventually hitting zero.

[SBMS]

4 minutes ago, JohnMo said:

The output of cooling is just the inverse of heating 

 

In simple terms if the room is 24, the floor would need to power of 63W/m² (700W /11m²), so floor temp of 24-6 (from chart below), so 18 degs floor surface temperature. As room temp gets closer to room temp output reduces eventually hitting zero.

So when designing the UFH loops do we need to target a w/m2 To account for cooling demand? Ie we need an output of 63w/m2 in this instance?

[JohnMo]

6 minutes ago, SBMS said:

So when designing the UFH loops do we need to target a w/m2 To account for cooling demand? Ie we need an output of 63w/m2 in this instance?

Up to you really. I didn't even think about cooling until after the first year in the house. So my floor is designed around 18W/m².

 

Floor surface is a property of flow temperature, pipe spacing, insulation below UFH and depth from surface. My floor runs at 18 to 19 depending on solar gain. The more solar I get the harder the ASHP works and cycle time increases from 10 to 12 minutes to a few hours. This brings down mean flow temperature, hence the difference in surface temperature.

 

Surface covering makes a big difference, carpets kill cooling.