RodW

I've been involved with a few projects using A2AHPs for heating and cooling PH buildings. Some have worked well with only a couple of (2-3kW) units, one on the bedroom corridor and the second in an open planned GF. In winter, bedrooms with the doors open will be at the corridor temp whereas closed rooms will be 2-3 cooler. Bedroom cooling from the corridor isn't as reliable. A bulkhead unit with supply ducts to multiple bedrooms with the return duct with a filter to the loft works better but approximately doubles the installation cost 2 -> 4K for that fancoil. A single unit upstairs is also fairly effective at cooling the GF provided that most of the GF windows are shaded by structure or awnings/blinds. 2-3 kW units will rarely need to run above their lowest level, which produces a similar sound level as the MVHR valves. The current PHPP assumes fancoil unis will be running at their lowest level when using mechanical cooling. Running ASHP heating or chilled water through a duct heater/cooling of a MVHR unit can work well but if the heating and cooling loads vary significantly between rooms it will be tricky/expensive to direct additional air volumes to particular rooms. It is also less effective and more costly than a single fancoil.

That is an interesting point. I assumed we would just move the space heating over to the ASHP but this would allow the heating to work with the TS if its hot enough. There would a link to the ASHP controller calling for heat when there is demand in the building and the TS is too cold. Would there be a volumiser attached to the ASHP that the diverter valves connect to?

Thanks, that is a good point.

Ok, I'll see if there are issues with a adding a second tank heated by the ASHP. The plant room is on the first floor but the structure is already sufficient for the existing tank. I wasn't involved in the TS sizing. It may have been sized to provide space heating and DHW with only a single biomass burn per day. The actual DHW usage is quite modest.

The space heating demand is less than the DHW. The solar thermal covers about half of the DHW i was hoping an ASHP could do space heating and the remaining DHW. The UFH is only to part of the GF and the duct heaters do make the FF bedrooms comfortable. I hoped that UFH and duct heaters would be linked direct from the ASHP,. They require different water temperature but possibly flow temps to the duct heater could be altered depending on the weather, to run longer at lower flow temperatures. The thermal store needs to stay to allow the biomass stove/boiler to be used, My original thoughts were: I didn't know if it is practical to get heat from the ASHP into the thermal store, it has 3 coils, 2 for solar thermal and 1 for the DHW. Water is circulated from the TS through the biomass stove. Maybe a plate heat exchange between the ASHP and the TS, using the ports no longer used by the space heating equipment, but that is another lossy step with additional hardware that will need maintenance. Not linking the ASHP to the TS avoids this. Are there conditions where it would make sense to combine the TS with a separate water tank heated by the ASHP? The on demand electric boiler idea is interesting for the DHW. If we adopt that route I am not sure if an ASHP is justified just of the space heating.

Hi, I posted the following a couple of weeks ago to the new users thread but I didn't get any responses. I'm trying to help an acquaintance, on an unpaid basis, to minimise the amount of relatively new equipment that gets discarded. If we are being unrealistic trying to retain so much of the existing system that would be useful to know. The installation is near Braintree, Essex. Many thanks, Rod

@goth Sorry, for confusing things by referring to winter performance but I haven't come across this issue previously so I mentioned situations where I would expect differences between upstairs and downstairs temperatures. Rereading the thread made me realise how ingrained my experience is of using nighttime cooling in summer. My own house is in a rural area and we tend to have 1st floor and roof windows open from May to October, only closing during hot days and opening again in the evening.

In a PH with an insulated ceiling between the GF and bedroom and no heating on the FF I would expect the temp in the bedroom to be 1-2 degrees lower than the GF. Have you looked at the walls/floor with a thermal camera to see if heat is leaking in from an unexpected source? I once looked at a PH certified flat where one of the bedrooms was unusually warm and that was due to missing insulation in the wall between the airing cupboard and the bedroom and a poorly lagged DHW tank/piping.

Hi, I work on ventilation systems and thermal modelling for PH buildings and I've stayed in touch with one of my clients from 2011. He specified the heating system that uses a large thermal store, Akvaterm 1000l, supplied with heat by a biomass stove and solar thermal. The DHW and space heating are supplied from the TS. Space healing is via UFH on GF and duct heaters in the MVHR supply air to the FF. There is a PV system on the roof but this is not linked to an immersion in the TS. The original heating contractor is no longer involved. As he has become older the level of physical work required to operate the stove every day through the winter is too high. He wants to retain the ability to use the biomass stove for special occasions/resiliency but adapt the heating system to include an ASHP. He has been contacting ASHP installers but none of them are interested in integrating with the existing TS. We know this will not be the best way to run an ASHP but the space heating demand of the building is very low. All the ASHP installers I know design for compliance with RHI so this is too left field for them. I thought I would ask here to see if retrofitting is a viable option or whether there is a better approach. TIA Rod