gravelld

Good to see some high performance building going on in Leicestershire, we seem to not have that much about! Whereabouts in Leicestershire?

I'm not talking about replacing a lead valley with a GRP one - I'm just talking about going over the lead valley with a coat of the GRP. I have also used those flashing patches successfully, and they do stick so long as the lead is cleaned up nicely. But they are even more temporary I think! Yeah they are fine fissures/tears in the lead. I think this lead is about 25 years old. One of the roofers commented the runs were too long - they should be cut to maximum 1500mm runs, he does 1200.

We've got some holes in our lead valleys and want them fixed. Two roofers have recommended just coating them in liquid GRP. A final roofer said it doesn't last and we should put in a new lead work and valley. Does anyone have any experience of liquid GRP and how long it might last? Trying to weigh up the cost/benefit.

There's also Lunos, if that still exists.

I found what it is... it's one of these: https://www.victorianplumbing.co.uk/bristan-jute-mini-twinline-thermostatic-shower-valve-w-adjustable-riser-ceiling-fed I think the generic term is "ceiling fed". "Twinline" is Bristan's name for it... I think. But I can't see it on their website anymore, so maybe this design is obsolete.

Since switching to mains pressure hot water I need a new shower in one of our bathrooms. It currently has a digital mixer (the type in the loft which just has one output which goes to the shower) which incorporates a pump and requires gravity feed pressure. It's started leaking - it probably shouldn't have been reconnected to the mains pressure hot. I would prefer a standard thermostatic shower but that would require running more pipe. However, I think it might be possible to have a thermostatic shower with one feed... In a different bathroom I have a Bristan shower that has one knob for pressure and one for temperature. The controller stands off the wall and takes one feed pipe. In the loft (above the bathroom) the hot and cold are merged into one pipe - this one pipe then goes through the ceiling down into the bathroom and into the controller. This was also downstream of a pump, but I don't think the pump was necessary. They don't appear connected in any way. It's not a digital mixer - there's no mixer unit as such. There's just a Y junction where the hot and cold are merged. It's like a normal themostatic shower, but the hot/cold feeds aren't where the control knobs are. If we could merge the hot/cold in the loft, like with the shower above, that would give the best of both worlds. What are these types of shower called? I can't see it anywhere on the Bristan website.

Flow temperature 45C (∆21.5) I used @ReedRichards' chart above (thanks!) and interpolated (in my head) a correction factor of 0.63 from ∆30. So basically there are four new radiators required, and swapping about of existing radiators in five other cases (out of a total of 23 radiators). The difference in RHI is £700 - I'm not sure if it's going to pay for itself, but it might be worth it anyway.

Flow temperature 45C (∆21.5) I used @ReedRichards' chart above (thanks!) and interpolated (in my head) a correction factor of 0.63 from ∆30. There are a number of rads that will need enlarging but it's not looking too bad atm. Some are way oversized, and some are in rooms with other heat sources, so I'm just going to wait on the response to my question above before I decide what to do. For a flow of 40C upgrades look a bit more pervasive but will check that later.

BTW, what are the rules regarding RHI, MCS etc when sizing radiators? Must the installer prove the radiators are adequately sized on a per room basis? I know they have to prove heat loss and the suitability of the heat pump, just unsure about emitters. For example, might it be ok to allow some rooms to be slightly undersized and other, next door rooms, oversized?

I don't necessarily doubt them as such. But almost every installer I have spoken to is hand-wavy about the numbers, doesn't want to discuss system design, doesn't really understand things like higher performance building and runs a model that doesn't allow for inputting of all necessary data (such as air permeability or Uw of windows) to produce an accurate heat loss estimate (granted, this might partly be the MCS influence). So I do think the models need checking. My original aim is to (1) keep us warm and (2) optimise cost and maintenance burden. I am yet to "realise" this, because it depends whether the cost of installing extra/larger radiators is covered by the increased RHI payments. I'll run some numbers tonight.

@ReedRichards SORRY IGNORE: that correction factor table is based on T50. I need one based on T30 if I'm going to use correction factors. [Just realised i can use the T50 correction factors by using the T50 output numbers from Stelrad at al] All of this is post MCS calculations!

Looking at the RHI figures then, going from a flow temperature of 55C to 40C will increase the grant by about £1.4k for the full seven years. However to work out how many radiators need replacing, I still need the outputs for the radiators for ∆16.5 (or ∆21.5 for 45C). I can't see charts for this anywhere. Anyone know where I can get this info? I'm just assuming there's a 5C difference in flow and return temperature, and the point for the delta is the mean of those two.

@ReedRichards -4.2C Yes, next stage is to understand the implications on RHI payments, and costs overall.

To make sure I understand the point you are trying to make: ... I thought this was about maximum theoretical output, because it's during the extreme weather you want to make sure you have enough output. i.e. if my rads were undersized, even if the HP was powerful enough to deliver the required Ws the emitters were not large enough, given the delta.

Yes,forgot to say i saw that. Either Stelrad copy and pasted or it's more confirmation ?