Upstairs - UFH, AC or Fan coils?

[SBMS]

28 minutes ago, JohnMo said:

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.

I think the challenge on here is that there are those in the reverse ASHP camp and those in the separate AC camp. I don’t think there’s anyone that’s had both and can say which is more optimal, comfortable etc. 

 

I think the neatest idea is running heat pump in reverse (it’s there anyway) but the added complexity of dew points, lagging

etc makes this more risky than AC. That’s where I am at moment. AC = guaranteed cooling, no risk. But more expense. 

[JohnMo]

5 minutes ago, SBMS said:

but the added complexity of dew points, lagging

Dew point is nothing complicated, people would have you believe there is, for some reason. House at 22 the dew point is around 12 degs. Keep above that the dew point issue isn't there. You don't need to lag pipes any more than you do for heating.

 

I would do A2A or A2W not both. Both can do heat and cool. Make you choice and move forward. You could look at Panasonic squares loop system also.

 

Things I like with UFH 

No noise, everything is hidden, silent. One switch to go from heat to cool. 

 

Thing I didn't like with A2A, drafts, but liked the coolness in the house. But got to a point where we switched the Aircon off and just slept with windows open (34 degs and 100% humidity) because the drafts just bugged us and made us feel dry.

[severnside]

We went with A2A with electric DHW. We reused warm air ducting in main part of house with a ducted unit and Split wall mounted units in extension.

This is much simpler setup and free cooling in summer with solar panels. Didn’t notice the hot days. If there is no UFH requirements then this is simpler solution. In winter heating is very quick and provides room level control. 

[SBMS]

11 minutes ago, JohnMo said:

Dew point is nothing complicated, people would have you believe there is, for some reason. House at 22 the dew point is around 12 degs. Keep above that the dew point issue isn't there. You don't need to lag pipes any more than you do for heating.

 

I would do A2A or A2W not both. Both can do heat and cool. Make you choice and move forward. You could look at Panasonic squares loop system also.

 

Things I like with UFH 

No noise, everything is hidden, silent. One switch to go from heat to cool. 

 

Thing I didn't like with A2A, drafts, but liked the coolness in the house. But got to a point where we switched the Aircon off and just slept with windows open (34 degs and 100% humidity) because the drafts just bugged us and made us feel dry.

Do the units natively support switching from heat to cooling or is it work to ‘put the heat pump in cooling mode’?

 

by my estimation it’d be around 4k for the fan coil units needed for cooling with ASHP versus significantly more (10k+) for a2a system. 

[Thorfun]

38 minutes ago, SBMS said:

AC = guaranteed cooling, no risk. But more expense

Extra installation costs for sure but when running it’s very efficient when just maintaining a room temperature 

[-rick-]

2 minutes ago, SBMS said:

Do the units natively support switching from heat to cooling or is it work to ‘put the heat pump in cooling mode’?

 

This is going to differ depending on manufacturer. Some will make it easy and some will make it hard. Choose a system that supports everything out of the box and you will have minimum problems. Assuming you plan to use an installer, find one who can sell the complete system. Now the planning restriction on heatpumps that cool has been lifted it should be easier to find.

 

When I looked for a system for my current place (before BUS existed) Panasonic seemed to be the goto for this. Ended up staying with gas as getting permission to put a heatpump in a flat (especially back then) was too difficult.

 

[Thorfun]

25 minutes ago, JohnMo said:

because the drafts just bugged us and made us feel dry.

With a ducted system there is minimal drafts that we can feel. 
 

but I agree with the wall units. Careful placement is required so you’re not sitting in the draft. 
 

one regret I have is not having the money for ducted system downstairs and having to have wall units instead. But something had to give as money runs out quickly!

[JohnMo]

20 minutes ago, SBMS said:

Do the units natively support switching from heat to cooling or is it work to ‘put the heat pump in cooling mode’?

Some ASHP do not support cooling at all, some require a few bell and whistles (cost adders), other do it out the box. To switch between heat or cool is generally a volt free input. I just use an spare light switch, that's it. DHW continues to work as normal in either heat or cooling mode.

[SBMS]

38 minutes ago, JohnMo said:

Some ASHP do not support cooling at all, some require a few bell and whistles (cost adders), other do it out the box. To switch between heat or cool is generally a volt free input. I just use a spare light switch, that's it. DHW continues to work as normal in either heat or cooling mode.

So if you switch the pump into cool mode but then the DHW falls for heat it reverts back to heat mode (and then back again to cool mode when water is heated)?

[joth]

1 hour ago, SBMS said:

I think the challenge on here is that there are those in the reverse ASHP camp and those in the separate AC camp. I don’t think there’s anyone that’s had both and can say which is more optimal, comfortable etc. 

 

 

I have done both, and shared some views here earlier today

TLDR separate AC is lower hassle if getting someone else to do it. All in one ashp is neater and probably cheaper, but you need to be even more the ball managing or DIY installing it

 

 

 

[JohnMo]

22 minutes ago, SBMS said:

So if you switch the pump into cool mode but then the DHW falls for heat it reverts back to heat mode (and then back again to cool mode when water is heated)?

Yep, just like below, centre is DHW heating, the blue sections either side are cooling. As soon as there is a DHW call the heat pump swops duty from cool to heat, the diverter valve moves to direct hot water to the cylinder, once complete it all reverts to cooling again.

 

[SBMS]

8 minutes ago, JohnMo said:

Yep, just like below, centre is DHW heating, the blue sections either side are cooling. As soon as there is a DHW call the heat pump swops duty from cool to heat, the diverter valve moves to direct hot water to the cylinder, once complete it all reverts to cooling again.

 

Thanks @JohnMo I didn’t realise it was that automated. That’s interesting. I got chat gpt to model my cooling requirements during summer and it spat out this graph taking in my heat loss and cooling data along with this description of how it generated it. It still has a peak of around 13.4kW.

 

 

🔍 The whole-house 24-hour cooling load profile I plotted is

not based on full peak (worst-case) loads

 

Instead, it is based on:

 

A synthetic sinusoidal profile interpolated between average and peak cooling loads

– using column W (Average Load) as the baseline

– and column AD (Peak Load) as the afternoon high

 

📈 What does that mean?

 

 

At 4:00 AM, each room is assumed to demand only its average load (e.g., from internal gains or mild solar).

By 15:00, each room is assumed to hit its peak load (from full solar and ventilation gains).

The curve is room-by-room, then summed.

 

[JohnMo]

Has the above assumed you leave all your blinds up and just let your room flood with heat. If so that's a flaw in the maths.  Also taking some basic things, if your windows are facing south and have no shading, the solar gain doesn't start until you get sun through the window, so late morning onwards. Your peak load is at 9am. So would say your windows are facing east, is that correct?

 

At 9am even on a hot day, it's still cool outside, so open the windows and doors have a blow through, as day starts to get warmer than inside close everything up. Let your cooling, whatever you choose do what it does.

 

AI is great but you need to add a dose of common sense, or you are down a rabbit hole, shite in, yshite out.