Simon R Posted November 12, 2021 Share Posted November 12, 2021 Our house is very well insulated and our heating requirements are tiny, in the range of 2.5kw for a 20 degree temperature difference. At the moment we heat the house with two towel rails, that are fed from a gas boiler. I'm considering installing a matrix heat exchanger in the flow plenum of our MVHR fed with water from a small ASHP to effectively replace the heating from the towel rails. Having looked at the available ASHPs and came across a suitably sized unit the 'AG Mini' intended for pools at less than £500 it looks a good option. It needs a pumped flow rate of about 1.3m3 and hour. Does anyone have any experience of these AG Mini units or spot a problem with what I'm proposing. The plenum box is plenty big enough for the heat exchanger not to cause flow volume issues. Potentially I can also run it in reverse in the summer to provide a little cooling (would only use available PV power for this). Link to comment Share on other sites More sharing options...
Marvin Posted November 12, 2021 Share Posted November 12, 2021 Just a thought.... You need to consider what will protect the ASHP from freezing and add antifreeze to the water... Good luck Marvin Link to comment Share on other sites More sharing options...
ProDave Posted November 12, 2021 Share Posted November 12, 2021 This will kill the idea: "Suitable for summer use eg May-Sept – requires an air temp of +10c and above to operate" At that price it will be VERY basic, and by the looks of things no option to reverse cycle and therefore no defrost function hence when the air is too cold it might ice up with no means to defrost. It also requires a huge water flow through large hoses, not compatible with a heat exchanger in your plenum box. 1 Link to comment Share on other sites More sharing options...
Marvin Posted November 12, 2021 Share Posted November 12, 2021 and another You need to consider the possibility of condensation being produced if the ducts/pipe run through the loft when cooling.. Link to comment Share on other sites More sharing options...
joth Posted November 12, 2021 Share Posted November 12, 2021 Also: Delivering 2.5kW via air is very difficult at the very low rates that an MVHR operates at. As an approximation, you can put in 10W per supply vent per °C rise (above the normal mvhr supply temperature, I.e. over and above 20C). So if you have 10 supply vents you'll need to be putting 45°C air in. The AG mini won't even reach that temperature, it would be difficult to deliver that through a matrix heat exchanger at low rates, and would be uncomfortable for anyone sat under the air vent I expect. Link to comment Share on other sites More sharing options...
Iceverge Posted November 12, 2021 Share Posted November 12, 2021 1 hour ago, Simon R said: Our house is very well insulated and our heating requirements are tiny Well done. Just stick an A2A unit somewhere. In such a well insulated building the heat will find it's way around anyway. I like the look of this one. COP of 5, Wi-Fi control and summer cooling too. https://www.orionairsales.co.uk/daikin-air-conditioning-rxm25r-ftxm25r-wall-mounted-25kw9000btu-inverter-heat-pump-r32-a-wi-fi-15085-p.asp Maybe next year once I see our kWh usage for the winter. 2 Link to comment Share on other sites More sharing options...
Simon R Posted November 12, 2021 Author Share Posted November 12, 2021 4 hours ago, Marvin said: You need to consider what will protect the ASHP from freezing and add antifreeze to the water.. Good point, the MVHR has a shut down temperature so should protect it. You can also get central heating inhibitor/anti freeze for central heating on boats. Link to comment Share on other sites More sharing options...
Simon R Posted November 12, 2021 Author Share Posted November 12, 2021 3 hours ago, ProDave said: "Suitable for summer use eg May-Sept – requires an air temp of +10c and above to operate" I had figured as it would be inside the house the 10+ should not be a problem. Regarding the flow rates .45lt/s is 'normal' for 22mm which equates to about 1.6m3 an hour and more than the units required flow rate. Link to comment Share on other sites More sharing options...
Simon R Posted November 12, 2021 Author Share Posted November 12, 2021 3 hours ago, Marvin said: You need to consider the possibility of condensation being produced if the ducts/pipe run through the loft when cooling.. Good point, the plenum box is right next to the MVHR which has a condensate drain. Link to comment Share on other sites More sharing options...
Simon R Posted November 12, 2021 Author Share Posted November 12, 2021 2 hours ago, Iceverge said: Just stick an A2A unit somewhere. In such a well insulated building the heat will find it's way around anyway. Ah, I think you're absolutely right. Why complicate life when there is an even simpler solution. Just got to love the build hub for a second opinion! Many thanks 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 12, 2021 Share Posted November 12, 2021 48 minutes ago, Simon R said: I had figured as it would be inside the house the 10+ should not be a problem. Eh? The ashp inside? Or have I had one bottle of Shipyard too many? Link to comment Share on other sites More sharing options...
Simon R Posted November 13, 2021 Author Share Posted November 13, 2021 9 hours ago, Nickfromwales said: Eh? The ashp inside? Or have I had one bottle of Shipyard too many? It does sound odd, but given the our MVHR installation it's easy for me to install the ashp in the MVHR exhaust to scavenge a little more energy. That way all the mods are in the same area and pipe runs are kept to an absolute minimum. Our mvhr has frost protection and so would protect the AG unit. However as has been pointed out by @Iceverge , the simplicity of going the inverter heat pump route rather than modifying the mvhr ducting and putting in water pipes makes a lot of sense. The only down side of this approach is that the heating/cooling is in a single area and will have to dissipate through the house rather than being distributed to all rooms by the mvhr. Link to comment Share on other sites More sharing options...
Iceverge Posted November 13, 2021 Share Posted November 13, 2021 1 hour ago, Simon R said: The only down side of this approach is that the heating/cooling is in a single area and will have to dissipate through the house rather than being distributed to all rooms by the mvhr. It'll amount to much the same thing in an airtightness house with MVHR. Heating the supply feed will heat the bedrooms/living rooms first but the hot air will need to travel through the house to get to the bathrooms/kitchen. Putting a heater in a central hallway will heat the air locally, then it will travel to the bathrooms/kitchen and back to the MVHR where most of the heat will be recovered and be distributed to the bedrooms. Get a cheapo plug in heater and experiment if you're unsure. 2 Link to comment Share on other sites More sharing options...
SteamyTea Posted November 13, 2021 Share Posted November 13, 2021 26 minutes ago, Iceverge said: Get a cheapo plug in heater and experiment if you're unsure. Always a good idea. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted November 14, 2021 Share Posted November 14, 2021 On 13/11/2021 at 08:19, Simon R said: It does sound odd, but given the our MVHR installation it's easy for me to install the ashp in the MVHR exhaust to scavenge a little more energy. That way all the mods are in the same area and pipe runs are kept to an absolute minimum. Our mvhr has frost protection and so would protect the AG unit. However as has been pointed out by @Iceverge , the simplicity of going the inverter heat pump route rather than modifying the mvhr ducting and putting in water pipes makes a lot of sense. The only down side of this approach is that the heating/cooling is in a single area and will have to dissipate through the house rather than being distributed to all rooms by the mvhr. And the conflict of fan speeds? Link to comment Share on other sites More sharing options...
Simon R Posted November 14, 2021 Author Share Posted November 14, 2021 1 hour ago, Nickfromwales said: And the conflict of fan speeds? I had intended to remove the units fan on the grounds the that the flow rate from the MVHR should provide more than adequate cooling. It was proving hard to get the information on fan flow rates for the unit to verify my assumption though. Going the aircon unit is so much simpler, found an entry from Mr Harris with some very useful stuff Link to comment Share on other sites More sharing options...
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