gravelld

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 But I can't see it on their website anymore, so maybe this design is obsolete.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 ?

Thanks all. Looks like Kudox's W/m2 for ∆50 works out around: 600x800 double convector = 1430W / 0.48 =~ 2979W/m2 600x1200 double convector = 2146W / 0.72 =~ 2981W/m2 Two sizes there to show the sizing appears to give roughly the same output per m2. Obviously this changes with rad type, e.g. single, double convector. Right now I'm just trying to get some confidence in the model figures. I compared the Kudox output figures to Stelrad's and they come out about the same - about 3% difference. So some agreement there. For ∆30: 600x1200 double convector = 1091W / 0.72 =~ 1515W/m2 Stelrad don't have a chart for ∆30 (instead they have a correction factor). Kudox's ratio is 0.508, and Stelrad's correction factor is 0.515, so more agreement. Now, comparing these authoritative starting points with the original model. The original model hardcoded 1480W/m2 as the output for a double convector. So actually, I think after all the original model was roughly correct for ∆30. If anyone could double check the above I'd be grateful. If the above is true, and we run a slightly higher flow temperature to meet ∆30, it means we have barely any rad upgrades to make.

Width and height - sorry need to be more careful.

Just looking at this again and I think I might have made more inappopriate assumptions... The W/m2 for radiators in the original model are given as: Towel 320 Single panel 640 Single convector 850 Double panel 1121 Double convector 1480 However, sources such as http://simplifydiy.com/plumbing-and-heating/radiators/power suggest this is less than the expected output for Δ50. I found some more sources and the figures are all over the place. Furthering the trouble is that these figures are hardcoded in th emodel so I can't see how they are derived. There's no reference to the flow temperature (and subsequent delta) for example. When I recalculated for a lower delta, I used the above figures as the start point and used a correction factor. But this is invalid if the original figures are not for Δ50. I've found it quite difficult, surprisingly, to find a straight calculator for W given delta and w/h of the radiator. Does anyone know one?

I worked my way through the 'model'. Turns out the model was using an assumed W output given Δ50. We are looking at more like a 45C flow temp, so I think more like Δ30 would be more accurate? Given that, I changed the model (it's just a Excel spreadsheet) and this gives over half of the rooms requiring larger rads. So thanks for making me go back to check that...

Sorry, yeah, not sure why I said "gut feel" - not much help!

From what I read LLHs can be used in a number of different scenarios. The installer is saying the two pumps on either side of the LLH can be run at different speeds and in addition the power output can be modulated. Thanks for the rule-of-thumb about running time and also the link to the study - I'll read in more detail later.

We have a fairly even split of traditional TRVs and smart ones (Heat Genius) which can be time programmed. The latter are used in the rooms we use most often. We also have two towel rails that are always open. I was told about 50l of water circulating was about right. I haven't measured the distribution network fully, but could give a ball park estimate. In terms of the rads alone it looks like about 150l but obviously that's only relevant when the valves are open. How does one get a gut feel for the size of buffer tank?

I kind of agree, but that's what the model says... I'll double check it.

I think I've found an ASHP installer I'm happy with, but one aspect of his design rests a little uneasy on me. Generally we have gone for slightly oversizing the heat pump and having a lower flow temperature to maximise the COP. The pump is a Midea 16kW. The house is a retrofit where we are swapping out an oil boiler. No UFH, all radiators. The heat loss and modelling has shown only one radiator needs to be enlarged. The bit that feels uneasy is that his design doesn't include a buffer tank for the space heating. Having been reading a lot of BuildHub in the past few years, it seems to me that default advice is to have a buffer tank to reduce compressor restarts (improving the life of the pump) and reduce short cycling. Instead of a buffer tank, the installer recommends "low loss headers or plate heat exchangers, both of which act as hydraulic separation". I am not a heating engineer, so I don't really understand the significance of LLHs totally. Reading around, it appears to be a way of allowing two circuits to run at different speeds. I am told Midea heat pumps can operate a second pump, and this is where the LLH comes in. Combined with modulation down to 15%, they think that a buffer tank is not required. Can anyone help me understand this better, or maybe give some ideas to probe a little more with further questions of the installer?

Vermiculite is the common suggestion up to the thermal envelope. Ventilate with a vent at top and bottom of non filled space. If it's being enveloped in EWI could you consider removing the top down to the level of the thermal envelope e.g. first floor ceiling if cold roof,then sealing that in? Then,no need to fill and the space might become a useful service cavity e.g. for ducting.

The EWI gets complicated quickly, if you're doing it right. Avoid caps at the top of the insulation e.g. at gable verges and extend the roof line instead. You might have to move drains. You might have to move meters. You'll have to extend any penetrations. Extend the insulation through the roof at any lean-tos to meet the insulation there (depends on cold/warm roof). Consider using higher performance insulation (e.g. aerogel) at the reveals. Ideally go further than 300mm underground, foundations permitting.

Tried JJ Crump?