Dillsue

Have CE done their MCS design to size your heat pump at 10.5kw? Did you or anyone else check their sizing?

Shame things haven't worked for you as it's so frustrating to have conflict. As in all walks of life, money talks so don't pay anything else until they've completed or you agree otherwise. For extra costs get a breakdown from them to understand what they are claiming for then go back to their quote/tender and see what they allowed for. If it says estimate or there's a quantified bill of materials then they may well be justified in claiming for extras but you need their breakdown of extras to understand the claim. In terms of delays you need to work out the realistic costs of the delays to work out of its worth getting into a fight with them. If you've got other work going on, fighting with 1 contractor over what may realistically be a few hundred pounds might not be worth the aggro. Remembering that you want them to honour any warranty and set the system up properly- having a fight over a few hundred pound might jeopardise aftersales

If your neighbours install solar in the future and everyone's systems start tripping on sunny days, who do you think is going to get shutdown when the DNO investigates? It's everyone's grid so why not stick to the rules and keep it working for everyone's benefit- you'd likely be a bit miffed if a neighbours unauthorised system kept causing yours to trip. In terms of enforcement, look up the National Terms of Connection which you signed up to with your electricity supplier.

Never looked at air tightness measuring but do you not need calibrated pressure/flow meters?

I'm just looking at factoring in ventilation losses and am struggling to understand suggested air changes! Seems a figure of 0.5 ACH is reasonable for a reasonably well sealed house. If I use this figure it puts the heat loss up by about 50% which is having a massive impact on radiator sizes needed to run at 35 degrees. If half the air in the house is replaced every hour that's 4 complete changes of air in the 8 hours were in bed. We don't have the heating on overnight as the house holds its heat fairly well. Seems implausible that the house is getting 4 changes of potentially freezing outside air overnight or it would be freezing next morning, which it isnt. Only explanation I can see is theres enough thermal capacitance in the fabric that can reheat multiple changes of air?? Is 0.5 ACH actually what happens or is that a figure the B Regs want you to aim for??

I don't know about Tigo or any others but SolarEdge has full monitoring of each optimiser/panel so you can see individual panel production. I think you can set alerts on their monitoring platform to let you know if any stop producing

I think panels are very reliable but if you do get a faulty one how do you know which one is faulty without monitored optimisers? Remember that panel shading can be bird s**t, algae growth, passing clouds, neighbours trees growing, future telephone pole etc etc. Optimisers allow easy expansion using panels of differing wattage. They also allow panels on the same string to face differing directions without reducing collective production. If you're using SolarEdge optimisers, batches come up on ebay at a fraction of retail price so don't have to be painfully expensive

Don't they spread install time over a longer period by identifying which radiators need changing then changing them at a later date? That could be repeated install visits over weeks or months with the attendant disruption of breaking into a working system??

AKAIK flexys fail way sooner than ridgid pipe so you want them out in the open where you can see them starting to drip. If they split in the cavity they could be there leaking for a long time soaking the building fabric rather than dripping onto the outside floor.

I was talking about on roof but applies equally to in roof as others have show

I think most panels/inverters/optimisers have at least a 10 year warranty. JAs warranty is for the end user and transferable to subsequent property owners. I'd guess most mainstream suppliers would be similar??

Not for me. Unless you mount them inside the roof then they are either integrated into the panel or mounted behind/under the panels. If you or your roofer are confident on the roof then it's only a 15 minute job to lift a panel, swap an optimiser and refix the panel. I have access to a rope and harness so happy to work off a ladder but with an alloy scaffold tower it's a breeze to lift a panel.

We've had a couple of optimisers fail and I've gone direct to SolarEdge for replacements and I think the panel warranty from JA SOLAR would be the same. I don't recall seeing anything in the warranty wording that needed the installer to make a claim.

Wow, thanks for all the input. We currently heat 95% with wood 5% lpg so I've no historic consumption figures. We'll be keeping the WBS and boiler to give a hybrid system although if we use the MCS umbrella outfit Im assuming we'll need to disconnect those and reconfigure after the HP is commissioned and signed off. There's wet UFH in the tiled kitchen floor set in an insulated concrete slab the rest of the house is rads which most will be getting swapped around or replaced sized to run at 35deg c. House is 270m2 built in 2001, low e DG, 75mm insulated cavity on the ground floor, 150mm insulated timber frame on first floor, 250mm loft insulation I have to work out how to factor in ACH but I'm not intending to size the HP for exactly the calculated heat loss as it needs time to do the DHW. With having a hybrid system the intention is to use the WBS/lpg boiler if the HP was struggling through a cold snap but in the 24 years we've been here those are few and far between. Weve got solar thermal and not averse to putting the immersion on occaisionally if the HP was busy with the heating. Based on the circa 4kw loss I'm thinking a 6Kw HP would give a bit of headroom for DHW and cope with the heating at least 95% of the time. Does that seem reasonable or is there more to consider??

We're planning on installing an ASHP later this year and just working through heat loss and resizing rads. Total calculated loss comes out around 4kw without any allowance for ventilation losses. Back in December we heated the house for a couple of days with 3 electric fan heaters running 24/7 while it was around zero outside and 4kw of direct electric heating kept the house at 18/19 degrees. This roughly aligns with calculated loss so am I correct in thinking this validates the calcs??? The reason for asking is an MCS umbrella company have suggested an 18kw heat loss based on floor area and fabric details I've given them. I appreciate that MCS guidelines drive a very conservative approach but the 18kw seems way over the top. Am I missing something??

I think the ex trial inverters are like hens teeth but interesting to know that the Quasar units will work outside of a trial

Great and keep it that way until you've done a full QA check. I have an inkling that if you complain to MCS they'll send someone out to have a look

Using 0.504 gives a dT50 equivalent 2530 watts radiator for bed 2 with the rad fitted seemingly around 2100 watts output. Given the gain/loss from the room below wasn't accounted for and some rads might not be positioned optimally, I think I'd be tempted to revisit all the heat loss calcs and verify rad sizing at least meets the heat loss. What you do now will likely be in place for decades and if you're upping flow temps to deal with undersized rads, you've potentially got decades of throttled COP!!

From stelrad tables a 600x1200 k2/type 22 puts out about 2100watts at dT50. That's a bit short of the calculated loss so how's things in the real world..... does that rad keep the room up to temp when it's freezing outside??

Having just bought a Leaf I'm intrigued to know how you've done the V2H interface. Have you been on one of the trials or via another route??

After a look at Stelrads conversion factors I think to get the rad size the table needs rejigging to divide the heat loss by the conversion factor. Your bed 2 would need a rad size of 1276/0.396= 3222 Watts at the standard dT 50. Is that roughly what you ended up with??

Not sure that applies to optimisers?? Certainly our Solaredge units run cool. Is the MCS guidance in respect of micro inverters and optimisers or just inverters??

The table has fixed rad sizes(existing??) showing the output at various flow temps to guide on choosing the minimum flow temp. I'm working on fixed flow temp/heat loss with a calculation to show dT50 equivalent rad output for running at 35c. I'm wanting to keep flow temps low to get a good COP so it's the rad size I'm interested in rather than the flow temp needed for a preset rad size. For your bedroom 2 the rad output shown falls way below the heat loss. Are you running like that??

So it's not a case of "you're not allowed" to install optimisers in the roof space, it's only an MCS requirement/guideline not to.

Did you do heat loss calcs for each room to size the rads and factor in the the massive reduction in output for low temp flow?? I'm working my way through all our rooms/rads just now to resize everything for 35 degree flow and intrigued to know the approach you took??