SimonD

GSHP at this depth is actually solar thermal rather than geothermal so the ground used for extraction of heat requires annual restoration by the sun otherwise it does not recover for the next heating season and why the ground array sizing is so important.

I just went to order some timber from one of my local suppliers, Arnold Laver, where I used to get really good prices and service. Website is down and I found this: https://www.constructionenquirer.com/2025/11/14/timber-giant-files-administration-notice/

"the European Development Fund" - oh the irony

Building Regs do tend to be open to interpretation, but what you can lean on and discuss with your BCO if it's a problem is that in accordance with industry practice and guidance (CIBSE Domestic Heating Design Guide) for any new build, a design temperature of 21C should be used throughout the building - because of higher insulation levels and we hope, better airtightness. In this sense, adjacent rooms can be considered as a single zone: 5.21.b

Yeah, that's what I did with the plywood sheets I used for the stringers for my construction stairs. They have a delightful bounce to them but have been plenty strong enough 😁

Ah yes, indeed. I just reread the technical document I had and realised that what I read - Differential Pressure Delta P - was just constant pressure not proportional, which is why I was confused by the chart showing constant pressure. I must read these things a bit more carefully next time! I think it's worth testing pump setting 0 to see what happens. Who knows, it may not work at all but if it were me, I'd like to see variation in flow rate proportional to burner and DT and then see what happens through the system. I wonder what happens when these things are installed with weather compensation, or maybe nobody ever does and they build these things for relay controls only for the UK market, just like other manufacturers like to reduce specs for us?

Good question. I hadn't really thought about it this way but may not be practical given the span is 3.3m so I'd have to sister the plywood sheets too.

Well, yes that was the plan and then I got the look from my wife when I mentioned temporary 😉 temporary that in true self-builder style becomes permanent, so I better plan ahead even though we have planning permission for another 1.5 width garage. So the ties/joists are rough sawn 50 x 100mm with no grading on them at all. They're installed every other rafter at 32inch centres (approx. give or take an inch or so as they vary ) , so I guess I'll either need to add to each rafter missing the ties. Span is 3.3m. As for load, that's a very good question. I'm not imagining anything particularly heavy, but don't really know what's sensible here. Do I go with the ceiling joist span tables by BSW and the C24 (my usual supplier only stocks C24 anyway) and use something like 45 x 145 or 45 x 170 for some extra margin? If I can get them in there, I still wonder whether new joists bearing on the wall plate might overall be the simplest way?

Solid wood for me all the way. For us, I've bought par redwood and machined with a router as I don't really like the standard profiles. Everyone I know who has had MDF has regretted it, especially if you have hard floors that get mopped.

Yes, but there is a rule of thumb to divide this (q50) by 20 to arrive at a leakage rate under normal conditions.

That's a very good question. I simply don't know. In my heat loss calcs I keep on going back to ventilation like a revolving door to find more accurate answers to more accurately calculate ventilation losses, but we know that standardised heat loss calculation methods almost invariably over-estimate ventilation losses. And the industry is set up to lock us in to the proscribed methods. If you deviate from the national figures, you have to be prepared to provide a rationale for the deviation, especially when it comes to retrofit. So again, this is more complicated the it first seems. Yes, assuming that the MVHR system does not impact pressure, then it would be in addition to infiltration. But from a ventilation heat loss perspective, it would be wrong to assume this simple addition given that, 1 the industry standards tend to over-estimate infiltration ventilation losses anyway, and 2 the effectiveness of the MVHR system. MVHR systems can suffer the same fate as heating systems in that many are over-sized (I know from data that this was definitely the case a while back and I would hope the situation has improved). The question then remains in each individual case as to the flow regime within the heat exchanger. If it is in the transitional or laminar state, then the efficiency of the MVHR is greatly reduced, which obviously impacts the ventilation losses significantly. Now if someone finds that they back off the flow rate after installation, they'll still get the benefit of fresh air, but without all the benefit of heat recovery. Obviously there are systems that deal with this by cutting off flow to parts of the heat exchanger to maintain turbulent flow, but tbh, since I decided to go the natural ventilation direction I haven't followed the MVHR market for about 5-6 years, so don't know the current market situation, but I would cynically doubt that this function has become a standard. Maybe I'm wrong?

I know the dilemma well. I actually used to work in Microsoft back in the 1990s. I have a dual boot system and spend most of my time on Linux with LibreOffice, but then boot up on Windows and use Excel only when I absolutely have to. It makes life a bit of a pain, but for me it's worth it. Ventilation losses are a big problem for the whole industry. Unless you've got the results from a blower or pulse test, it's pretty much guesswork anyway and then you've got just a few options on methodology - you've got SAP based on storey height, location, exposure etc. or BS EN 12831-2017 or CIBSE methods and they usually treat MVHR differently so I'm not sure MVHR would correctly be an extra leak on top of ACH.

Most of these boilers are thrown on the wall with configurations never touched by the installer and in default I believe the 8000 DP proportional pressure 250mb. In most scenarios, it provides sufficient head to supply most houses where they're installed. I'd be very surprised, given the pipe oversizing indicated earlier, that the index circuit is anywhere even close to needing 4m residual head. This approach to me is tantamount to the plumbers who set the pump on 3 and run out the door. But I agree that the system behaviour isn't right - you've got constant flow rate of 21.5lpm. and modulating burner output and reducing DT until it seems to find equilibrium at burner output of 49% during the test. If the pump is on Delta P proportional, the flow rate shouldn't be the same at 49% burner output because it doesn't need it and it's therefore creating unnecessary pressure drop through the system - e.g. the system fighting itself. The tech info is a bit ambiguous here because it says the pump can be set to proportional Delta P and if this were indeed correct, there needs to be a change in flow rates somewhere sometime - on any decent modulating system there should be variations in both DP and DT as heat load and output change. Why not test in fully proportional linked to burner, which is what most sensible boiler manufacturers do out of the box? You can probably see now why I don't have anything to do with these things from this brand.

Both the ods and xlsx file work fine in LibreOffice calc. Best thing to do is download and install a copy of libre office - https://www.libreoffice.org/ But beware, once you start using it instead of Excel, you may never go back 😁 Now need to do some interpretation.

On all these, it shows pump at 100%. A correctly modulating boiler should modulate the pump too. As flow temp rises and dt falls, I'd expect to see additional modulation, including from the pump as the gas valve throttles back. Has this boiler been set at constant pump speed? If so, this might be fighting the boiler?