Mr Ben

Apologies for hijacking this thread, but wondering if you’d mind sharing what sort of COP you’re seeing at the minute and longer term from the aquarea units? Moved in to new build at the end of October, 12kW J series T-CAP, seeing a COP of 3.0 for December which I’m pretty disappointed with. (300m2, 16mm UFH both floors 150mm centres, not zoned, constant call for heat with weather compensation running flow temps of 24-29 and 3 degree delta T) I think the unit is probably massively oversized for the house, also potentially running glycol and a 50L buffer tank in series hurting the efficiency.

Yea, this is where the problem lies. I'm limited to 130mm because of the requirement for 100mm drop from house FFL. XPS + 55mm screed + 5mm wearing layer is what's proposed. I'm thinking phenolic PIR has basically half the lambda value of XPS, but only 150kPa.

175mm of TLA in the house. Maybe less than I'd have liked if starting from scratch, but not awful?

This might be the way to go

200mm is under your garage or house? It's not really an occasional space in terms of heating, but I'm not looking for house temperatures. Stable in the low teens through the winter would be ideal.

Thanks Conor. 50mm of PIR would give me a u value of 0.25, it's far from ideal but surely enough to make the >300% efficiency of heating with ASHP worthwhile over a plug in electric heater?

In my head it makes more sense to use ASHP to heat the floor and gain the benefit of its COP. May also need to cool in the summer.

You're probably right. What I really want is thermal stability for fermenting and storing beer rather than a comfortable workshop temperature for a few hours.

This is my main concern, although for a target temperature of 10-15 degrees and an otherwise pretty well insulated structure I don't imagine it'll take an awful lot of heating for most of the year. Part of me wonders if adding insulation is going to make more problems with overheating in the summer, and whether I'd be better just insulating the slab along the two exterior sides to get more thermal mass in the form of concrete. I presume not because the bison beams would still act as massive cold bridges

Question for those that have used single wire temp probes - what are you connecting them to? I've added a half dozen DS18B20 probes into my floor screed with the aim of protecting hardwood floor from overheating, and maybe eventually integrating into home assistant to be able to trigger UFH pump to circulate if big differential develops due to solar gain or occasional use of woodburning stove. Ideally I'd like some sort of networked box that can log temperatures without necessarily needing to buy a raspberry pi.

MVHR is Brink Renovent Excellent 400L

Thanks Declan, I want to add UFH pipes with the aim of keeping garage temp in the low teens year round for man cave activities, in particular home brewery and bike trainer. Garage was included in heat loss calcs / system design, and thermostat and manifold have already been installed. It's 5.5 x 6m, 100mm PIR in wall cavities and 400mm rockwool in loft, well insulated sectional door (Hormann). The standard spec is for 100mm slab of c30 concrete. After much deliberation builder is proposing 60mm of 300kPa XPS with a λ of 0.036, and 60mm of thermal screed for an additional £4000. I'm limited by NI building regs requiring 100mm threshold between garage and main house, which BCO is apparently interpreting as strict 100mm change in floor levels, so pretty restricted in total floor height. Concerned that's a lot of money for not a lot of insulation, and not a lot of thermal mass. Thermal stability is as important as absolute energy use, in my head I'd rather have concrete with a lower emissivity than a thermal screed designed to turn on and off like a radiator. Ideally I'd like to use 50mm of 150kPa PIR with λ 0.022 under 75mm of concrete. I can't find a lot of information on compressive strength needed under a garage slab, most of what's online seems to be converting a garage into habitable space. Sanity check, if my car weighs 2200kg and I jack up half of that weight on a scissor jack with a 13 x 25cm footplate that adds 3300kg / m2 of pressure, or 33kPa, just over 1/5th of what would compress insulation by 5mm, before even considering the safety margin in the insulation product and the load spreading of a concrete slab. Question - does this seem like a reasonable approach?

Hi All, Many thanks for all the incredibly useful advice here! Brief introduction - buying a ~300m2 new build from developer. House is beam / block construction with a cold roof, and was already watertight before we first viewed it in the Spring. It's not been designed to be particularly energy efficient (when questioned their target air tightness was "better than 5m3/h/m2"), but developer has a good reputation and they've been relatively tolerant of my requests such as improved air permeability and replacing gas boiler with ASHP. I feel like a bit of a fraud compared to the many true self builders on here, however dealing with a developer and an existing shell has definitely presented its own set of challenges. Have ended up with a 12kW Panasonic Aquarea monobloc, a 300L mixergy tank, and pipework at 150mm centres with minimal zoning rather than a stat in every single room. Air tightness is being addressed with a combination of rubber paint to exposed blockwork, vapour barrier membrane over joists, wet plaster throughout and an additional / intermediate pressure door test, with the aim of improving to under 1. Current preoccupations are how to insulate under attached garage floor, and how to monitor floor temperatures. Not sure if I should start new threads to ask for advice, or if its ok to post some questions in the introduction thread.