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Resurrecting an old thread... this is copied from the PAUL guide referenced. The internal RH of the summer daytime normal heat exchange is 74%. The internal RH of the enthalpy setup is 60%. So I'm not sure it's a like for like comparison? Also wondering if the enthalpy exchanger would help with dehumidification if the house is being cooled in summer?

Great thread I'm a little late to. If trenching anyway, wouldn't it make sense to duct refrigerant lines through solid pipe e.g. 110mm soil pipe, and insulate around the soil pipe e.g. with a combination of XPS and spray foam? That would allow changing out the lines if needed, and minimise losses. I presume the air held in the soil pipe would be static and a reasonable insulator. I wonder if pre-insulated refrigerant lines could be run through the soil pipe, and if that would make much difference vs just insulating outside the soil pipe.

https://mhclgmedia.blog.gov.uk/2024/11/21/warm-homes-plan-and-heat-pumps/ Great news, the 1m from a boundary requirement for PD is to be scrapped. In worse news we didn't know this when we submitted our planning application in Dec 2024, to include a heat pump down the garden and by the boundary (mid- terrace). So we've now poked the planning and noise assessment bear. Any idea when this will actually come into force? I can only see references to early 2025.

I realise this is the wrong time of year to ask...but what have people's experiences been of cooling at temperatures above the dew point? This will surely increase humidity, and actually get below the dew point in a controlled manner would be beneficial for the humidity. Was there any need to run a separate dehumidifier? If you had MVHR, what settings did you have to mitigate this? We would have upstairs UFH in P5 chipboard, so moisture control is critical, downstairs TBC. I feel like I might end up 2 loops with the option to set them at different flow temperatures: (Loop 1) UFH and (Loop 2) insulated pipework with FCUs. I have a decent Home Assistant automation setup and independent control of each would be really useful. Running both loops at the same temperature would allow a minimised flow temp and maximised COP. If we want a rapid warmup we can run the FCUs at a higher temp than the UFH. If we want a rapid cool down we can run the FCUs lower than the UFH. To dehumidify when cooling we can drop the FCU temperatures below dewpoint and/or increase their fan speed. We could even increase the UFH flow temperature accordingly to prevent overcooling. This does beg the question of why not purely fan coil units. It's not a gigantic property (160sqm after extension). We'll be fitting new flooring to much of it anyway e.g. for the kitchen & bathrooms I think there's a clear benefit to UFH above FCUs.

Do you then have two loops, one for the fan coil+buffer and one for the UFH? How do you control this? The Panasonic (I think) heat pumps allow two zones at different temperatures. I wondered if there was an easier way of achieving this with other models.

I can see that if you bring in warm air into the cool house the relative humidity will increase- so in this instance reducing airflow through an MVHR would be beneficial. They may reduce a little of the incoming air's moisture as it is cooled by exhaust air but I doubt I huge amount. Perhaps the main pitch for the comfopost should instead be for dehumidification as part of a larger cooling setup.

I'd see the ability from fancoils added to UFH to preferentially cool certain rooms (e.g bedrooms) handy. Without UFH too, I'd go below the dew point using insulated pipe and condensate drains. With the UFH, taking the fan coils below dew point would I think require two loops, a diverter, and a volumiser for the fan coils loop? Unless you can run one coming loop at 7 degrees C supplied in insulated pipe, then blend the UFH to a temperature above dew point? I can see the argument for just adding AC, but as additional outdoor unit wouldn't suit our property (mid-terrace).

So all of this has confirmed for me that a comfopost isn't worth it for us. If you're running fancoils on the same loop as UFH, presumably that gives plenty of circulating volume. It would then run offset above the dew point, accepting achieving less than maximal cooling/heating output from the fan coils. It seems to me there's little point in running insulated pipe to supply the fan coils? And is there any need then to provide a condensate drain for the fan coils?

I initially thought 3 fan speeds seems a little basic, however the panasonic FCUs are only 4 speed https://www.bpcventilation.com/panasonic-fan-coil-unit

is the summer house also UFH? How do you take the water loop from your house to the summer house, and how far is it?

Thanks Dan, your comments on that other thread I linked were very helpful. My understanding is that if you have active cooling, the MVHR should cool intake air using exhaust air if you disable the summer bypass? Are there any benefits you can see you the comfopost additional to fancoils +/or UFH at all? I.e. if money were no object (unfortunately not the case) then could you argue for both comfopost plus the UFH/fancoils?

Hi John, what's the floor area and the floor construction inc covering your UFH is in? Was this ground floor only, or upper floors? That's superb efficiency and personally I'd see the money as well-spent to maintain a comfortable temperature. I still come across lots of people who happily burn oil to heat their house to 25 degrees but think it's unacceptably wasteful to apply cooling using (renewable or even self-generated) electricity.

Yeah I had looked at the datasheets- the largest comfopost can do 2.8kw cooling (ERV MVHR) with 600m^3/hr air flow. So noisy and limited cooling- but I think it's useful to get actual experience of that too. There's another useful thread on here from someone who decided against heat battery/cooling in the end.

Exactly the clear answer I needed! Out of interest though, have you got any data through HA about it? What size heat battery have you got, and what flow temp and air flow were you using?

I forgot to include the link to the product I was referring to- these are what I spotted https://aerfor.com/en/reverso

I've also spotted these recently. I don't love the look personally but appreciate the price and flexible mounting options. I presume these would also give the option for some individual room control of cooling (for examples different preferences for bedroom temperature), although with the small buffer volume issue that's been already mentioned. It also strikes me that the optimal positioning and airflow direction does vary between heating and cooling applications, but I don't know how much difference that would actually make.

Dave, how has the heat/cool battery attached to the MVHR performed over the summer?

Hi all, I came across this post on another forum about reducing the cold bridging across sash boxes. I wanted to see if there was any experience on here. https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16668 I am refurbing my old sash windows in a 1905 mid-terrace. The main plan is retrofitting vacuum insulated glazing, draft stripping, and replacing the mastic joints. We'll be adding internal wall insulation, either Thermactive plaster or PIR, with a plan to boost ventilation (MVHR) for moisture control within a major refurb. We have a single storey bay window with 3 sashes in. I was putting expanding foam behind the mastic where the joint was large, and it seemed to be an endless void. Turns out the boxes aren't complete and are open to the stone on the external face. This is a big cold bridge, with only 20mm window frame and ~100mm stone between inside and out. Obviously foam in here could bust out the boxes and would definitely stop the weights running. I was wondering however about sheathing the weights in plastic pipe e.g. 40mm waste pipe, and filling the remaining cavity with loose fill insulation. Any experience with this/recommendations/cautions?

Thanks Dave, this is fantastic to see and very interesting. What period is that cooling accumulated consumption over? Or do you have a measure for how much heat you've been able to extract over a day? And could you share your approx. floor space? Do you have data for your dew point in the summer? I presume when it's hotter, with incoming air being cooled as it passes through the MVHR, you'll have a high relative humidity and a higher dew point, so the flow temp to the underfloor heating will have to be substantially higher than the 13.3+2 celsius dew point offset above?

Amazing. This is the essentially setup I want to go for. Loads of questions! How much cooling performance do you get? How much additional cooling do you expect from the MVHR? Any buffer in that system, or is there enough volume already? What kind of flow temps are you typically running at with the dewpoint offset? I wonder how much cooler you could run water to the fancoils (using insulated/vapour barrier pipe) if it weren't for the UFH, and the difference in cooling performance? I believe the Panasonic ASHP can do two sides at different temperatures, so wondered about having loop A with a dewpoint offset for the UFH and then loop B at 7 degrees for the fancoils and MVHR

Hi, I couldn't find an answer to this by searching but suspect BH may have good advice. We're planning a wraparound extension and L-shaped dormer to a mid-terrace house (as attached) and I want to pre-empt future roof access. I don't want to rely on the neighbours' side return for access. A future owner will inevitably build there. For the neighbours' amenity, planning will only let us have a pitched roof on the wrapround extension rather than flat, insisting on a pitched design. We need to maximise internal height relative to the allowed party wall height and probably will have a box/hidden gutter here. The left slope is 25 degrees, the right 9.5. Roofing will be EPDM or GRP. We'll have skylights in the extension, one in the loft above the (otherwise very dingy) stairwell, and perhaps one in the bathroom on the outrigger of the loft (although I'm concerned about solar gain from this). The front access of the house is 6m to the soffit with a 35 degree roof- this could be used to access the loft skylight but the rear loft window would still be a problem. I want to make sure we can clean the extension skylights, 3x 1st floor windows, 2x loft windows and 1(/2)x loft skylight. I also want to consider roof maintenance and gutter cleaning. There's a chance I'll get solar panels put on the loft too, also needed cleaning. I spoke to some window cleaners who seemed very gung who about this but I'm concerned they might actually struggle. And other trades with heavier tools/materials might think differently. Grateful for thoughts on the following please: Does anyone ever build in treads to a roof e.g. GRP, to allow walking along a slope as we have on the left, or even some sort of lugs a ladder could be braced against? Would an opening skylight in the loft bathroom be the most sensible way to clean the loft skylight(s)? Is there a value to pre-installing something high up that a ladder can be secured too- like a eyelet/attachment point. Am I just underestimating other people's ability to work at heights?

Are you trying to get this done under permitted development? I've not looked again at PD rules: they're online or someone else here will likely know. We just had a pre-application meeting with planning to discuss an extension after a previous refusal based partly on the boundary wall. This will be a wraparound extension with a wall on the boundary of 10m, on the right of the image. We quoted precedent from a property on the street who used a 25 degree angle from the breakfast room window facing the extension (above wheelie bin). The planning team indicated this should be ok for us too (but we're waiting on the report). They didn't make any reference to the neighbours' French doors from a dining room (middle of image) nor the kitchen patio doors (left of image).

I'm early on looking into this cooling. Planning to cool UFH at ~15 and fancoils at 7-8, so running at 2 temperatures. It looks like the Daikin Altherma 3 all-in-one can do bizone heating at different temperatures- so presumably could do bizone cooling too? This would avoid the need for a buffer.

I think it would be lower energy per time, but would need to run constantly for frost protection. So would probably end up using more? Ultimately if the electric version was pricey, it could stay buried and never used without issue- not the case with wet UFH.

The gate sounds like an interesting application. Out of interest, was the track installed to allow for drainage or do you have pooling and freezing water?