epsilonGreedy

Thanks for the hard numbers. My unit of measure is an average sized house. Consider a house with a 10m long southern wall and eaves 5.5m high. An hour's worth of ASHP air volume is 1600 m3 at 4kW demand. On a sunny crisp still winters day a warmer pocket of air might form measuring measuring 10 x 5 x 5 = 250 m3. In contrast on the north wide the property wall and ground will be colder. It is not implausible that the COP will be a few % higher when heat is extracted from slightly warmed up air. Anyhow combating frosting is the principal point of interest.

I am a philosopher and historian, numbers are tedious. I was giving you an opportunity to demonstrate your mathematical magnificence.

To a scientist of your calibre it should be entirely possible. Start with the heating demand of the house. Next the heat capacity of air. Heat extracted per m3 of air can then be calculated based on the typical drop in temp as air flows through the ASHP. Add a twiddle factor of efficiency loss in the ASHP. Then you have you have your air volume.

You deserve some thoughtful answers to this question. My hunch is the high stress of such a project could exacerbate the medical conditions you are dealing with. Given the assumed cash situation you will also need to think about temporary accommodation during the build. I would look to purchase a bungalow and renovate it to suit your requirements, this will still be a large project but an order of magnitude less stressful than a whole selfbuild. What internal living area are you contemplating or is specified in the kit house you have found? With this internal square meter target others can provide better advice.

No one is suggesting positioning a new build house elsewhere on a plot so that an ASHP gets the prime sunny location. Likewise there has been no discussion of remote siting of an ASHP in the sunny corner of a plot. The matter of debate is: given equally viable ASHP locations on a north or south facing wall what advantage will be gained on the southern wall. Putting aside the summer chilling function I think we all accept there is a theoretical advantage on the southern wall but is it a 0.1% reduction in heating cost or 5%? It would help if you and @SteamyTeacould concur on the volume of air drawn through an ASHP. @SteamyTeasays "several tons a day" and you are claiming "up to" 3.7 tons an hour. Anyhow the real point of interest is ASHPs that are prone to frosting. Let's not forget the COP of an ASHP in defrosting mode is negative 1.0 or is it negative infinity? The worst outcome is an ASHP that spends so much time defrosting there is not enough time left to maintain the required internal house temp. Someone reported such a case here recently. Would a southerly aspect help such edge cases?

@GreatescapeI think you need to re-appraise what is achievable in this renovation given your starting point. A ceiling height of under 2.25m throughout the property will feel oppressive and could undermine final market value, so that rules out UFH unless you commit to digging out the concrete slab but that will raise your renovation cost to the point where a knockdown and rebuild could make more sense. By the end of next week we will be looking at a kWh price of around £0.30 and at this price point ASHPs only make sense for the highest spec Passiv houses that can be heated overnight at an Economy 7 rate. Such homes can retain enough heat during the day and top up with more kWh the following night. Your renovated home will be way way short of this performance criteria. With that floor you will struggle to better an EPC band C score. Let's review what you can do: If a solid concrete floor then the current U value will be too horrible to calculate and even worse in a bungalow it represents a higher proportion of your external surface area. Loft space, yup a U value between 0.11 and 0.15 is realistic providing the roof pitch is not lower than 30 degrees. Walls. Probably around a U of 0.30 currently. Lining with 52mm thick PIR backed plaster board will get you down to 0.20 but that will be quite expensive and in a smallish 60 m2 foot print you will loose 2" to 4" off some room dimensions. Windows: Given floor heat loss and likely final market value of the finished project it is not worth going mad here and putting in 3G Passiv house type glazing. My advice is new gas heating, UFH in the extension only and maybe MVHR if your air leakage score is below 3. In your position I would go back to the architect and say you accept the thermal performance of the main building will always be so-so. So you want to zone the property and create a thermally high spec 45 m2 of daytime living spec, insulate the heck out of the 15 m2 contributed from the original building to create this space. I am imagining a kitchen/snug with 75mm of PIR under a wooden floor and 2.2m ceiling height, then stepping out into an open plan 30 m2 extension with UFH and 2.5m ceilings.

This would be a persuasive point if true when an ashp is located with a southerly aspect. I was predicting a continuous process where the metal case warms a few degrees above ambient temp then radiates some heat into the ashp mechanics. The case heat capacity is not the significant measure.

@TerryEI would be interested to know what EPC rating your house has? It would help me understand how your experiences will map onto my, likely lower rated, property. Also how many 420 heating mode days do you clock up a year? And finally do you have enough data make that final decision on whether an ASHP makes sense?

Well yes indeed because they require a consistent reading not affected by the sun popping out from behind clouds. Your post in effect confirms how influential direct sun light is at warming things up. The benefit derived by an ashp situated with a southerly aspect will depend on how many heating demand cycles per hour and the duration of a cycle. As you indicate ambient air temp will eventually determine whether the internals of an ashp get to the frosting point but an ashp bathed in sunlight will start with a higher temp advantage. You also seem to dismiss any warming of the air mass on the southern side of a property. The onus is really on you to disprove human intuition and life experience on this matter since we all know that sitting in the shade is usually chilly in the UK.

Some follow-on questions for @Mr Punter about his installation: Does the black sheathing protect the white pipe at the entry point into the slab or is it there for another reason like brutal tilers? Do you reckon you have the optimal height for your manifold? I ask because in my small house I reckon the best location for the manifold is under the stairs however the UFH pipes will be laid before the stairs is fitted which means I will have to do some precise measurements to ensure the under-stairs manifold cabinet is workable.

Your photo offers encouragement. I followed link from @Nickfromwales to the following product https://underfloorparts.co.uk/product/unimix-blending-4-port-underfloor-heating-manifold-with-grundfos-upm3-pump-uni-mix-temperature-control-mixer-valve/ In the description is says "the Uni-Mix Valve must be fitted on the left side" which got me thinking. So maybe the manifolds are ambidextrous but the add-on bits are left or right handed.

I am thinking ahead to the routing of the hot feed into my UFH manifold and it would be simpler to position the circulation pump to the right of the manifold. All examples I can find show the circulation pump to the left. Is it feasible to position an UFH circulation pump to the right of a manifold? My UFH installation will be for 60 m2 on the ground floor with just 4 loops and 2 zones.

A low heat capacity, high thermal conductivity metal case sounds like the perfect design to create a solar powered defrosting unit. As the case warms up it will radiate half its heat inside the case thus creating a micro climate to defrost the inner works of the ASHP. I have long felt the claim that ASHP position is not affected by direct radiant heat from the sun to be dubious. One of a few established forum beliefs that needs to be challenged.

Surely this confirms what people observe, namely the ground on the sunny side of a building can be frost free when the shaded north side suffers a multi day permafrost at this time of year.

Very interesting. A few years ago I remember a discussion here where I mentioned my concern that flowscreed might end up as a thin concrete crust lacking support from the insulation below. My concern at the time was that if PIR compresses it does not rebound back to its original shape unlike a cheaper spongy insulation sheet. I now realise that concern can be mitigated by installing a thin starter insulation sheet using a more elastic insulation sheet below the main layer of PIR and/or using sand to fill dips in the base floor. Thinking about about a point I raised above I don't suppose leaving the UFH pipework filled with water creates enough weight to keep the insulation sheets pinned down? Ho-Hmm I am starting to consider a traditional sand/cement screed again in the hope the extra weight keeps the insulation snugly weighted down to the base floor. Having watched many screed insulation videos I do not recall seeing use of these knock in pins. Is this an example of the industry solving a new problem that has come to light as thinner flow screeds are used?

That is a lot of holes in the first membrane.

Did you mean can't get under the insulation? If so I thought a second membrane over the insulation prevented this? Does pouring screed with the UFH pipes filled help prevent lifting? Are these "knock ins" a type of intersheet jointing fixture?

Safer thicknesses would be 50mm and 75mm respectively.

Was the evolving design your own design from the outset or did you have the debug the initial pro installation?

A professional letting agency would declare a lack of heating at this time of year to be a critical situation that must be resolved within a few days. In view of your other thread just the declare the rental property to be uninhabitable and move back into your nearly rebuilt house. Is the deposit held with a 3rd party?

Given the cumulative diagnostic effort to get @joe90sorted I wonder if there is merit in the collective brains of this forum specifying a BuildHub no-frills UFH reference design? If it was uploaded to GitHub under a creative commons licence then future self builders could ask suppliers to quote for bits to install the reference design.

Are these heavy lead batteries or lithium batteries? If lead then you only have 1.6 kWh of daily usable capacity in that bank.

Thanks. What does it mean? A quick Google suggests it is the estimated final market value on completion.

Ok I will bite, have been here 4 years now and that is a new one on me. Guestimated Determined Value?

No. I found 120mm high fascias to be problematic. 150mm is smaller than average. You need to consider the following: The pitch and tile overhang dictates the top lip of the gutter and this will be lower than the fascia top. You need to factor in the extra height of the roof battens on top of the rafters. Some tiles/slates look better with a bit of upwards kick in the first eave course so the fascia top will be higher than that calculated for the batten allowance to support the kick.. Gutter systems have brackets have different heights and you want to make sure the bottom of a bracket does not droop below the fascia. The gutter will need a gradient so having calculated the minimum fascia height for the 4 points above, add the gradient. Finally if ground drainage requires a downpipe at a specific position then double check the wall plate is bang on level. In my case the wall plate was off 5mm the wrong way against the planned gutter gradient which caused some head scratching given my already slim 120mm fascia. A 372mm overhang is unusual but if you want that you will have to abandon the idea of resting the soffit on top of the last course of facing bricks and fit hangers that drop off the rafter tails to provide fixing points for the soffit. This assumes the masonry is complete.