tanneja Posted July 20, 2021 Share Posted July 20, 2021 Our current setup is a combi boiler (existing before our renovation and relatively new) for our heating and HW demands. It is connected to the wet UFH for the ground floor. These temperatures have me concerned that our house will need active cooling. I have an idea for where to place an ASHP for managing the climate of the upstairs bedrooms, using a 3 or 4 way split unit located on the flat roof. For the downstairs, there are minimal routes for services. The downstairs seems relatively cool anyway, but was considering slab cooling (polished concrete floor finish throughout) via a second ASHP (instead of air con wall units where wall space is at a premium). While I hope I don't need any active cooling, in case we do, my builder and plumber have asked what valves would be needed to connect the ASHP to the UFH for cooling purposes, whether to build that into the pipework being put in place at the moment. It likely makes sense to worry about it if the situation ever happens, but checking in case. If I ended up needing that cooling from the slab, would it mean having the ASHP govern all my UFH and UFC, leaving the combi for the upstairs rads and hot water? Or would it make sense for the combi boiler to still manage the UFH, with cool provided by the ASHP on some kind of intelligent valve? Link to comment Share on other sites More sharing options...
PeterW Posted July 20, 2021 Share Posted July 20, 2021 Two 3-way diverter valves. Link to comment Share on other sites More sharing options...
tanneja Posted July 20, 2021 Author Share Posted July 20, 2021 3 minutes ago, PeterW said: Two 3-way diverter valves. Thank you Peter, I guess that is one for flow and one for return. Are those diverter valves smart, based on a thermostat demand? Link to comment Share on other sites More sharing options...
PeterW Posted July 20, 2021 Share Posted July 20, 2021 Yes so you don’t put cold water through your DHW Link to comment Share on other sites More sharing options...
PeterW Posted July 20, 2021 Share Posted July 20, 2021 Sorry misread this - are you saying you are using a gas combi for DHW and floor heating and just the ASHP for floor cooling..? Or are you saying you will use the combi for DHW and the ASHP for heating / cooling ..? Link to comment Share on other sites More sharing options...
tanneja Posted July 20, 2021 Author Share Posted July 20, 2021 (edited) 14 minutes ago, PeterW said: Sorry misread this - are you saying you are using a gas combi for DHW and floor heating and just the ASHP for floor cooling..? Or are you saying you will use the combi for DHW and the ASHP for heating / cooling ..? I am saying I am open to either approach. Probably the latter is the one that makes sense. I don't like the idea of the UFH being totally reliant on the ASHP in case a severe winter where it may struggle (that might not be a realistic concern), but to the layman it seems 99% of the time having the under floor heat and cooling fully managed by the ASHP appears to be best, with upstairs rads and hot water via the combi. But these are just my very high level guesses, reassurance as to the best system would be very reassuring. And if there were benefit to sympathetic pipework at this stage, we aren't too late to incorporate. Edited July 20, 2021 by tanneja Link to comment Share on other sites More sharing options...
PeterW Posted July 20, 2021 Share Posted July 20, 2021 Ok so you want a hybrid heating system. So you need to look at why, as running UFH at 40°C or less is the sweet spot in terms of performance. Not sure - unless you’ve got Rads upstairs - then a high temp supply from a gas boiler becomes irrelevant. Link to comment Share on other sites More sharing options...
tanneja Posted July 20, 2021 Author Share Posted July 20, 2021 11 minutes ago, PeterW said: Ok so you want a hybrid heating system. So you need to look at why, as running UFH at 40°C or less is the sweet spot in terms of performance. Not sure - unless you’ve got Rads upstairs - then a high temp supply from a gas boiler becomes irrelevant. Thanks Peter, indeed we have rads upstairs, and our combi is 2 years old so plenty of life left. Link to comment Share on other sites More sharing options...
PeterW Posted July 20, 2021 Share Posted July 20, 2021 Ok so you’re probably now split zoning everything … and gas is cheaper than ASHP for heating to a point so need to be careful here. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted July 20, 2021 Share Posted July 20, 2021 Combi for DHW. ASHP for cooling and heating with cheap low grade heat. Combi for heating for the depths of winter. Hybrid ASHP’s can have either gas or oil burners to do exactly this. Controls will be the difficult part. Personally I would fit the 4 splits upstairs to purge unwanted heat and see what effect that has on the overall overheat issue. Nothing beats air-con in bedrooms afaic, ( I’m looking at a 5 split system for my own house atm ). I think it would leave things manageable with the splits absorbing and exporting excess ambient heat from the upper floors vs it just stagnating. Note: the 4 and 5 way splits operate with intelligent load shifting, and only allow full potential to one problem area. The remaining units have to share the residual kW power rating so some rooms suffer the lower output. Basically you cannot exceed the output of the main unit. Eg you may have a 12kW outdoor unit and 4x 3.6kW cooling capable units but they’ll never all achieve full potential. 1 Link to comment Share on other sites More sharing options...
tanneja Posted July 20, 2021 Author Share Posted July 20, 2021 @Nickfromwales thanks that is so helpful. What kind of quotes are you getting for supply (and install) of 4/5 multisplit unit? Will the routes to the room be out of sight and fairly easy to get access to? What is the typical diameter of the internal pipework for the multisplit units? I presume there are separate flow and return required for each internal unit back to the external unit? Link to comment Share on other sites More sharing options...
Nickfromwales Posted July 20, 2021 Share Posted July 20, 2021 DIY for me, up to the point of gas and F certification etc. This lot for around £750 a unit ( supply only ) isn’t bad, but cheaper makes can be had. I’m seriously tempted by this. Link Due to the limited combined outputs of the multi unit splits, I think I’ll end up with 2x Link covering 2x units in workshop and office and then the rest doing the 3x 1st floor bedrooms and 1x attic bedroom. I can then point the max outputs at the biggest / most problematic spaces. The controls can be set up to allow one indoor unit to demand more of the outdoor units power to make sure that that particular space has sufficient cooling. Pipe kits and gassing need to be priced on top, and even with me buying and running all the lines and power etc ( also don’t forget about the condensation drains from each indoor unit to a suitable drain ) I expect to spend another £600-£800 on top of those prices. Hiding pipes and cables will be down to how much labour money you throw at the project. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted July 20, 2021 Share Posted July 20, 2021 Air con pipework is 8mm and 10mm copper in most instances. It needs to be wrapped in black neoprene high grade insulation also. Would fit in , say, a 40mm waste pipe if you need some idea of footprint. Plus a garden hose sized condensate pipe, plus cables ( communication and power with some ). 1 Link to comment Share on other sites More sharing options...
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