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Designing my house system with a mix of air to air and air to water

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(@pipebaron)
Active Member Member
Joined: 2 weeks ago
Posts: 6
Topic starter  

Hi Guys, 

 

I hope you're all good. I recently got a survey and vent test done on my property that shows my heat loss to be aruond 6.4kw. It's a three bedroom house with a converted garage as the living room and my office at the back, and then a dining room and kitchen. Upstairs are two bedrooms (east and west) and a bathroom, and then the loft is now a main bedroom with ensuite. I'm fortunate enough to have a spectacular solar system with 26 panels coupled with a 11kwh battery which will have meant our heating bills are pretty much zero. I want to upgrade the heating system to heatpumps and have been getting some quotes. 

 

This has been on my mind for the last year and I'm a regular listener to the podcast (which is superb!). However, this is my first proper post on the forum. 

 

My property has an east to west aspect, which means we get lots of sunshine and solar gain n the dining room and living room, and also my daughters bedroom. We've got a pretty good starting point with 28mm 15mm pipes and double panel convector radiators throughuot, some radiators are oversized (like in my office) and others are undersized. We currently use our multifuel burner in the living room in the evening with a recoheat which gives us plenty of heat across the house and creates a nice convection current (it works very well). We have the heating on pretty much 24/7 running as low as possible and I act like a human weather compensator to get the most from the combi boiler. 

 

With all of this in mind, I was thinking creatively about heatpumps and the way we generally use the house. This lead me to think that actually a single 4kw split AC unit in the living room could work alongside a wet ashp to provide constant background heating to the rest of the house. We have the doors open downstairs anyway, so it's fairly open plan. When the sun comes out the AC unit can go off. I'd still plan on having some rads in the living room and dining room, but move the bigger ones upstairs and the smaller ones downstairs to balance the system.

 

In terms of electricity usage cost, I like the idea of having a single split system heating the house up from 3 till 5:30 on the cheap octo tarrif and then have it set back to work on low throughout the day and have the wet system make up the rest of the heat. It seems like having some control on making good use of the cheap electricty at night, without overheating bedrooms is a good option. I know I could just put big rads downstairs and smaller rads upstairs, but that would mean solar gain issues which happen between 2 and 5 currently. I also like the idea of having a form of cooling in the summer when it's too hot and the sola inverter is kicking out heat, and finally, if one heating system fails, we've got some kind of backup that's cheap and green to run. 

 

Does anyone else run a system similar to this?? 

 

Cheers!

 

Richard



   
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(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 3164
 

I don't but I do have an a2W system with one fancoil and 2 radiators that have had fans added on a DiY basis. The rest is conventional rads.

If I were doing this again I would have had a couple more fancoils.  Their ability to heat rapidly, the fact that they can also lightly cool (which is all that I need if I'm sensible with windows and curtains on the few days it's really hot) and their small size is attractive.  They look good too at least to my eyes.

I can see the argument for combining a2a with a2w, but for me the sheer simplicity of one unit with one controller that just keeps the house warm throughout with minimal fiddling wins out, and fancoils bridge the functional gap sufficiently well.

That is of course a very personal choice.


4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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dgclimatecontrol
(@dgclimatecontrol)
Estimable Member Member
Joined: 3 months ago
Posts: 44
 

Posted by: @pipebaron

Hi Guys, 

 

I hope you're all good. I recently got a survey and vent test done on my property that shows my heat loss to be aruond 6.4kw. It's a three bedroom house with a converted garage as the living room and my office at the back, and then a dining room and kitchen. Upstairs are two bedrooms (east and west) and a bathroom, and then the loft is now a main bedroom with ensuite. I'm fortunate enough to have a spectacular solar system with 26 panels coupled with a 11kwh battery which will have meant our heating bills are pretty much zero. I want to upgrade the heating system to heatpumps and have been getting some quotes. 

 

This has been on my mind for the last year and I'm a regular listener to the podcast (which is superb!). However, this is my first proper post on the forum. 

 

My property has an east to west aspect, which means we get lots of sunshine and solar gain n the dining room and living room, and also my daughters bedroom. We've got a pretty good starting point with 28mm 15mm pipes and double panel convector radiators throughuot, some radiators are oversized (like in my office) and others are undersized. We currently use our multifuel burner in the living room in the evening with a recoheat which gives us plenty of heat across the house and creates a nice convection current (it works very well). We have the heating on pretty much 24/7 running as low as possible and I act like a human weather compensator to get the most from the combi boiler. 

 

With all of this in mind, I was thinking creatively about heatpumps and the way we generally use the house. This lead me to think that actually a single 4kw split AC unit in the living room could work alongside a wet ashp to provide constant background heating to the rest of the house. We have the doors open downstairs anyway, so it's fairly open plan. When the sun comes out the AC unit can go off. I'd still plan on having some rads in the living room and dining room, but move the bigger ones upstairs and the smaller ones downstairs to balance the system.

 

In terms of electricity usage cost, I like the idea of having a single split system heating the house up from 3 till 5:30 on the cheap octo tarrif and then have it set back to work on low throughout the day and have the wet system make up the rest of the heat. It seems like having some control on making good use of the cheap electricty at night, without overheating bedrooms is a good option. I know I could just put big rads downstairs and smaller rads upstairs, but that would mean solar gain issues which happen between 2 and 5 currently. I also like the idea of having a form of cooling in the summer when it's too hot and the sola inverter is kicking out heat, and finally, if one heating system fails, we've got some kind of backup that's cheap and green to run. 

 

Does anyone else run a system similar to this?? 

 

Cheers!

 

Richard

The A2A would be mostly if not all free if you have so much PV and a large battery. Mine is most of the year. It'll be cheaper and far quicker to work than A2W. Most people leave most doors open so its often ideal to have A2A running in the background and turn up when you occupy any room its in. We keep one of ours on all day at 21C Quiet fan speed (you cannot hear it) and that flows into three rooms then the hallway.

 



   
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(@pipebaron)
Active Member Member
Joined: 2 weeks ago
Posts: 6
Topic starter  

@dgclimatecontrol  Amazing, it sounds like it's a good idea. You're basically running it how I imagine we would, just trickling and feeding other rooms.



   
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(@pipebaron)
Active Member Member
Joined: 2 weeks ago
Posts: 6
Topic starter  

@jamespa I've not considered fan coils before! Can you share some examples and what to look for in the specs?

 



   
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(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 3164
 

Posted by: @pipebaron

@jamespa I've not considered fan coils before! Can you share some examples and what to look for in the specs?

 

Sure. Mitsubishi ilife2 slim is the one Ive got.  Panasonic do something similar.  Myson ivector is another, Smiths Ecovector a low end one.  Jaga Strada are a range of fancoils made to look like conventional radiators, they are almost a hybrid.  Then there are plinth heaters designed principally for kitchen kickspaces.  There are some incredibly swanky ones 9at equally swanky prices) made in italy, as is the mitsubishi one (and maybe the panasonic).

They tend to be quite expensive but a radiator of the same capacity, typically a type 33, is also expensive.

In terms of spec output obviously, appearance, noise level and look at what the controller does, which is worth checking. 

Mine is almost perfect, it modulates the fan according to measured room temp which means its very quiet most of the time.  The one fault is that it doesnt switch on in heating mode until the flow temp reaches 30 which is too high (my min flow temp is 27).  IIn cooling mode it switches on if FT<20 which is fine.  For now Ive wired a resistor in parallel with the thermistor to fool the controller into thinking the flow temp is higher than it is, but I will need to add a relay to switch this out (or just manually disconnect it) for summer.  What a pain, why didnt they make the threshold adjustable?

None of these will do cooling as well as proper aircon, its 'light cooling' with the water temp typically just above dewpoint.  If you want the house at 20C when its 35 outside you will need more.  If you are content to close the curtains and to get some relief from a blast of cool air fancoils should suffice.

Incidentally I dont think there is anything fundamentally wrong with your plan to have a2a + a2w but you need to think about the control aspects (you dont want two controllers fighting each other) and load in relation to the minimum output.  If your A2A is doing 4kW and your house is 6kW, your a2W needs to produce only 2kW max.  Thats very low and bear in mind most of the time the house load is half the design load (because OAT isnt at design value).

One thing to add, fancoils have very little water in them so system volume can be small if you use a lot.  In this case you will need a 2 port volumiser (you may anyway) plumbed into the flow preferably but the return if thats all the installer will do.  Dont let anyone talk you into a buffer, low loss header or plate heat exchanger between heat pump and emitters.

Hope that helps, keep asking questions and reading several opinions/viewpoints as you converge on whats right for you!

 


This post was modified 3 hours ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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(@pipebaron)
Active Member Member
Joined: 2 weeks ago
Posts: 6
Topic starter  

@jamespa Cheers James, it's great reading. In quite a few ways I've experimented with this stuff by using 80mm dc fans on my type 22 and that works really well, but it's very basic! These rads look excellent. All of your points about the heating system and use of a volumizer

 

I thought through and imagined already, but no problem there, more volume the better I understand. 

In terms of the a2a + a2w, In my mind I'd have the a2a working at very low levels and purposefully relocate smaller rads downstairs and put the bigger rads I've got in the bedrooms and spaces further away from the living room. At it's lowest level I believe the a2a unit I'm looking at produces about 900watts of heat and to maximise efficiency I wouldn't push it to capacity, effectively enabling the heatpump to run at lower flow temps (but I'd probably need to add in some system volume to smooth out it's use). I find having the capacity to have a a2a unit kick out a lot of heat just before I take the dog out for his 6am walk at off peak prices very appealing too! 

Posted by: @jamespa

Mine is almost perfect, it modulates the fan according to measured room temp which means its very quiet most of the time.  The one fault is that it doesnt switch on in heating mode until the flow temp reaches 30 which is too high (my min flow temp is 27).  IIn cooling mode it switches on if FT<20 which is fine.  For now Ive wired a resistor in parallel with the thermistor to fool the controller into thinking the flow temp is higher than it is, but I will need to add a relay to switch this out (or just manually disconnect it) for summer.  What a pain, why didnt they make the threshold adjustable

That is very annoying! For a product designed o work with heat pumps why are they putting such a silly limitation in there??? 



   
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