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If you look at the pump curve above, you will see "H/M" (M is meters) right at the top and it states right at the bottom that H is the Residual head. Residual head is the pump head available after the boiler HEX, you can see the pump head just starts falling, 1200LPM (21.7LPM) @ 7.0M head which indicates to me that the boiler HEX has a pressure loss of 7.0-4.0, 3.0M at a flowrate of 21.7LPM, you are getting very close to this flowrate, 21.5LPM at full pump speed. The residual (remaining) net head of 4.0M is lost through the CH system. If you now install a LLH where the primary pump just circulates through the boiler HEX and a (new) secondary pump circulated through the CH system, then, all the secondary pump head is used to increase the flow through the CH system which will increase the return temp/reduce the dT and get a increase in rad output and a faster warm up. If you install a "6M" secondary pump then the flowrate will increase from 21.5LPM to, 21.5*sqroot(6/4), 26.3LPM, not a lot as the rads dT will only fall from ~ 12C to 10C which only gives ~ 3% in rad output, say a increase of 0.6kW from 18.0 to 18.58. The easiest way to get a faster warm up is to increase the flowtemp to say 75C but would need reducing again when roomtemps reached to maintain reasonable boiler efficiencies. When the engineer next attends ask what the pressure loss through the boiler HEX is, dP & flowrate.

Tony, what's done is done, anyway, there are occasions where you may for one reason or another needed to get some sub structure in place, it's called speculative desgn. That's actually ok! You have an outside envelope into which you need to fit structure, the external appearance and materials have been established, happens all the time so take that as a positive. The first thing and I'll say again, what you are doing design wise is really hard especially the detailing! This cavity tray detail for example does not work, not least as the piece of masonry on the inner leaf will just come loose when you bed the cill, probably before that, there is no insulation under the cill. The shaped insulation is not achievable. What will happen is that you will end up paying for something that does not get delivered on site. I've looked over your thread and conclude. You have set you heart on the outside, it looks great. You have an established plan for the general internal layout and finish, again good! But you are struggling with the structure, how you insulate that, do the interfaces work thermally but also provide the lateral structural restaint and connections to the main structure. Now I've distilled your probem down. So all of a sudden that looks a bit more hopeful! What has happened is that as you have learnt more about the bit inbetween the outside and the inside you are discovering that it is hard and often I think the case here with you is.. you can't see the wood for the trees. This is not uncommon so don't take this as bad. It happens to many people, even those who do it as a day job! You are not alone! Consider trying to find someone who has the skills to review your design in the whole, identify a way forward that is buildable, knock heads together when required. That includes knocking you into shape. Many self builders are stubborn! That is ok at times but from time to time it can be to their own detriment. They pay professionals, but only from the neck down! Someone like this will work with you very closely and explain where your ideas are good and where you are going wrong. At the end of the day it's you paying the wage, it does work! Now that will cost you but for that you get not least, an advocate, a friend and someone on your side. In my experience the fee you pay is often offset by the savings made and enjoyment you get when someone says.. you are on the right track, always have been, but we need to add this critical bit. I'll leave these thoughts with you.

Steel will be the answer. It covers big spaces economically. My rule of thumb is that adding an internal column under a portal frame will reduce that frame by 1/3 in tonnes and cost. What width of building do you intend? You don't want a column in the middle of your space I'm sure, so make this a fundamental requirement, and accept the cost. OK, so they should be able to look after you, and will be charging. So anything we say on here might concern them as distrust. Have you given them a budget? Would any of them know how to achieve it?

So the knotty areas so far have been: a) Ventilation requirements: some serious kit and duct sizes involved b) Fire Strategy: means of escape/staircases c) Structural design: achieving a very large column-free main prayer space, without a crazy steel bill I was referring to the professional team (architect, SE, MEP, PM, Interior Designer). Despite having a full professional team engaged, I certainly plan to keep asking questions here, and keep sharing any findings.

It doesn't have to be fancy special stuff. It is stopping fire from spreading through a cavity so even wood will usually be suitable.

Interesting... so if using electricity - then might as well go for electric UFH - interesting and will put it to the team

a service void is nice to have but I'd prioritise the headroom. Anyway, that 830mm vertical bit could be widened to be a SV without affecting headroom.

I've done a few of these, design and construction, including a church, with the starting point being 'someone says you will be able to half the price we've had from tenders'.ie it's not a cathedral and so funds are tight. It is complex, based on the use, or variable uses, of the facility, and also the size. Ventilation can be a huge issue as is means of escape , if the numbers are large. Even which inclination of church and their procedures can make a difference to performance and choices. But to start with I don't know what you mean by a Composite deck screed. Does that mean your own steering group, or are there professionals advising?

@Nestor appreciate the pic - thanks

Yes it’s all fine. We had ours done just before Christmas. We used airtight osb board. Installers cut a hole, pumped, replaced hole and taped with a pro clima patch. Most were okay but i went round and taped the edges anyway this weekend ( took me a day).

In winter I need the 3 charging windows of cosy due to a small battery and big usage from the heat pump. The other 9 months of the year solar replaces those charges and ASHP usage drops dramatically, so Go is cheaper for charging the EV and the battery once a day (8.5p/kWh vs ~14p/kWh). If you do enough miles, it can make sense to stay on Go year round, so some due diligence is needed as my setup will not fit everyone.

Work out average daily consumption for each month. Put 20 units of each day or whatever the average is if its less than 20, into a battery at 8.5p=£1.70/day cost for 20 units to use during peak rate. At peak rate of 32p/unit the 20 units used during peak time would have cost £6.40 so there's £4.70/day saving. December's saving would be £4.70x31=£145.70. With my usage I'd get that Nov-Feb, a bit less Mar and Oct and quite a bit less for the summer when the HP isn't running and the PV is going full chat. Total for me is just under £1100/yr. 30kwh of Fogstar batteries and 6kw solis inverter is just under £4k. I'm also hoping to be increasing PV export by exporting most of what we currently use by using the battery and off peak eleccy rather than the PV. Not as lucrative as the peak to off peak saving but it's a bit more in the savings pot. That's a rough estimate based on current Octopus Go rates and doesn't include charge/discharge losses. With 30kwh of batteries I think I'll be able to use more than 20kwh of off peak eleccy which will hopefully offset the system losses?? Figures pan out for me so just fine tuning things before taking the plunge

Yes, I fixed PB next to OSB on the sloped ceilings. Service batten only fixed to walls.

We can't leave the ASHP on for our hot water. I wouldn't feel confortable to be honest. Water was literally pi$$ing out of the tundish. Someone asked if it was hot or cold but I can't remember. I think cold.. Yes and no. They did but in the hoo haa of the wrong email/billing issue it went to the wrong email address. I was then able to ask and get this resent which I posted on here. Leaking tundish is on our Gledhill water tank. The only pressure gauge I can see is the one on earlier photos and pictures. I spoke to the company today and have booked them in, hopefully Wednesday. I know @Nickfromwales you will be cursing me but frankly we are stuck. We have visitors later this week and an Airbnb booking so it is a case of sucking it up because the timing could not be worse. We used the gym showers tonight but we dare not turn on the hot water ASHP and have a lot of water coming out. So this is what I am going to ask: 1. We want to keep those expansion tanks. Told they need replacing but saw no evidence of this. We want to check them/see this (if they remove them is there a way of checking they have failed if they remove them)? The service form says they need replacing so this indicates they have failed. Do companies routinely replace them or pump them back up?? 2. We will explain what happened with the pressure dropping to 0, how I topped it up and the leaking tundish. Ask them to check valves are not faulty.

Nope. Direct electric is near 100% efficient. I did I’ve an external heat generator, then wet manifolds, plus ongoing maintenance, losses, and the I detect nature of heat delivery, you’re going to be worse off unless the cost per kwh is managed; so gas or heat pump.

I would get this right before going anywhere near a heat pump. I would rather chew my leg off than put PIR in a cavity wall or between roof timbers. Why the combo of EWI and cavity in the new build? I would do one or the other. Why so little EWI? The insuation is a small cost vs the install and render. Wait.........do hear a greasy haired white toothed kingspan salesman boarding a plane..........I think he's off to Marbella for a jaunt on the kooltherm sales he pawned off to you via your architect......

They failed to do due diligence, just an assumed 2x dead EV’s at 5 years old. Sugar coat it if you wish. This is just shit service.

Yep, if no services, put the PB straight onto the PP board without a gap. Gives you a little more heardoom.

Didn't the company send in a quote for remedial work together with a service report??

If you use Excel it's straight forward to do room by room heat loss calcs. Work out the area of each surface x U value x temp diff and that's your heat loss. If a surface has an element with a differing U value ie a window or door, deduct that elements area from the main surface and work out that elements loss separately, if it has a differing U value. Add all the losses for each surface of the room, 4x walls+floor+ceiling, and youve got the room loss. Repeat for each room and you've got the whole house loss. Simples:) After that you need to account for ventilation losses and I can't remember how I calculated that without opening up my laptop which I haven't got access to!! Someone else will likely guide you on that??

The entire upstairs is within the roof void. We have a steep pitch and a short wall height before the steep pitch starts. Having reviewed our lighting and power plans, we have no need for a service void on the sloped ceiling, and losing 37.5mm for the sake of it would be noticeable to the headroom and useable space in the room. I’m wanting a sanity check - is there anything I’m missing? The sloped roof will be all boarded with airtight pro passive board, and I would assume we would screw the plasterboard to it as ‘normal’ (should we be aware of / consider any other way?) Thanks

Are you able to share that wheeze with us. That a very short payback. One i would consider.

Im inclined to think this is the most likely version of events, with its obvious effect in pricing. I dont need another expensive hobby.

Guess I should have looked at the spec correctly - yes 25A, not 100A.

I'm particularly surprised by your suggestion for "screed electric heater wires" - my understanding was that wet pipes are much more cost effective to run.