JohnMo

I tried them, but due to my post code, they wanted both my arms and legs in postage - made them way to expensive. Wasn't sold on the design service either, cram floor full of loops, one spacing fits all rooms. So designed and sourced myself.

I think you maybe somewhat overthinking this. Have you calculated what bridging you actually get? Then ask yourself are the gains worth it to remove the bridging?

Write here comparing properties of each material https://www.theplasticpeople.co.uk/blog/polycarbonate-vs-acrylic/

If you don't have radiators, or on S or Y plan boiler, do you need one?

Insensitive moment - Is that another way of saying, a spoilt sh!te.

Add "Scottish Building Regulations" to your search. Get information like this from source. Then you actually know what is correct or otherwise.

Here you go, a simple image search, explain how it all works and how to adjust. ST.04.04.00 - Control Unit For Underfloor Heating System.pdf

First thing to remember is this setup is heat pump specific. So is basically playing with the coldest water for as long as possible. As long as the water goes back into the cylinder without too much churn the cold should stay at the bottom. So say the bottom of cylinder is at room temp (20 Deg), the heat pump would start flowing at approx 25 (dT5) then slowly ramp up temp as the return temp increases. So slowly heat over 40 mins + until bottom of cylinder gets to same temp as above the thermocline. If this isn't hot enough, it will just continue heating from the bottom - similar to a bottom immersion.

There are a couple of intermittent heating modes to protect the heat pump, the anti frost one - circulation pump on at or around a sensed 5 degs. The other is to keep the lube oil above dew point and a crankcase heater will fire up but is generally 30 to 40W. Neither really explain the the spike you see. As @JamesPa says the ASHP may be firing to keep the buffer happy. If the circulation pump runs all the time (some do by default) and it's cool outside the the temperature of the buffer will over an hour or so will drop, possibly enough for the heat pump to fire up. Why with no demand for heat? A buffer cuts the heating system in half and both are hydraulically separate. Your thermostats depending on wiring may only affect the CH side and not the ASHP side. So your timer may only be stopping the CH circulation pump. That is just a poor excuse for sloppiness, there is no reason not to set up now. He knows the design temp of the emitters, so first attempt should be pretty close. By running a schedule you are running a higher than required flow temp - so a hit on CoP, the buffer is another hit on CoP, fixed flow temp another.

May depend on what your thermostats are set too. Maybe the house has started to cool more over night than it did, and is now hitting your set back temperature, so heat pump is blipping heat in to keep things happy. Aren't you running weather compensation?

A fail closed valve with secondary contacts. Valve opens on call for heat, once open triggers pump to start. Keeps it simple, charge when not likely to be used, as whole tank will be stirred up. No cold water draw by accident, no new holes, ok efficiency wisey

The trouble with approach is the two two exchangers can start to work against each other. If you have the PHE as a primary HE, the heat source water leaving the PHE has had all the heat removed, so then can act as a coolant in the secondary coil. Would take plenty of calculations and compromises.

I'm in the same place. I have all sorts of expensive stuff that comes up on eBay for pennies in the pound sat in the plant room.

https://www.outsourcedenergy.co.uk/shop/ 8 port manifold £160 16 euro cones £36 600m of pipe £560 Bits and bobs £60. Staples 500 £20 Shop about around £800-900 all in

But adding in to the equation - the odd penny extra to reheat the cylinder, takes a long time to recover several hundred pounds spent.

Plenty of systems out there most are pretty much the same with a different label. 16mm Pert-al-Pert pipes for every loop. Single zone Don't waste any money on any self balancing stuff - not needed. I use Ivar manifold - zero issues. Got everything from outsourced energy, put plenty of suppliers. You need pipe Manifolds, ideally get a manifold with auto bleed bottle on the top of the manifold not on the end, as this isn't at a high point. Manifold isolation valves. 16mm euro cones for each end of the loop pipe.

Believe there is another pump for that and it's only used for immersion use. It's mentioned in the thread I linked to . Not sure you would get those conditions with a heat pump as the it runs a low dT typically 3 to 6 doing DHW. A heat pump will slowly ramp up temp to maintain a set dT. This way the CoP stays high. The heat pump will generally keep the same flow rate through out the DHW reheat. A typical DHW heating cycle. The CoP is the falling blue line. The grey shaded area is the input electric which increases as CoP falls. So secondary side flow rate would remain at a fixed rate. The difference in approach temperature would drive the primary temperature rise as it maintains dT by adding to flow temp

The screed depending on specific heat capacity will do one or the other not both well. Idea of concrete storage Slab storage For ~100 m² × 100 mm slab: Concrete volume = 10 m³. Mass ≈ 23,000 kg. Heat capacity ≈ 0.88 kWh/K per tonne. Storage ≈ 20 kWh per 1 K rise. So find the heat capacity of screed and compare

As @Nickfromwales I did similar but surface mounted up/down lights. So there are no electrics in the roof section at all. I put a service cavity there but never used it. Didn't even put any MVHR up there. Don't put lights high up, you need a scaffold to replace bulbs etc.

The Mixergy one isn't injecting a 1/4 of the way up, it may enter cylinder a 1/4 of the way but the pipe then drops to the bottom of the cylinder - it deliberately at the bottom, it takes water from bottom puts it back there warmed up. Mixergy don't use a PHE setup for boilers, PHE is designed specifically for heat pumps, to give best CoP.

Couple of ways to look at UFH. 1. Low and slow, so run at lowest temperature, to keep house temperature stable. For this thermal capacity of the floor is helpful. 2. Batch charge, using floor as a storage heater, again thermal capacity is needed. 3. Run like a radiator system, so thermal capacity acts against you. Here you low thermal capacity is needed and thin screed. So what do you actually mean by this?

I am flow 4.5L min per kW, doing DHW and 3.5L min per kW, doing heating from ASHP.

If you look at the mixergy discussion I linked to earlier. The water is taken from the bottom of cylinder the injection point is about 1/3 up the cylinder and then piped down to the bottom again. Reason this is good for a heat pump it is always working in the coldest part of the tank, holding back flow temp rise for better CoP. Hot water will float to top naturally. Would also be good for a boiler as it would hold back on increasing flow temp as long as possible. The main issues injecting high is 1. It destroys stratification instantly as you get a cold slug of water hitting the top of cylinder as cycle starts 2. You have to heat top down, so no hot water available until 45 Deg hot water comes out of PHE.

I have a normal cylinder, no-one even asked if I had a borehole. 25 year guarantee means nothing - they may not be trading. Not sure of your grade of stainless steel but, Stainless steel 316 can be used for the entire pH range from 0 to 14 (provided the chloride content <500 ppm). Edit just looked, SteelFlow is made from Duplex so even more corrosion resistant

Rye Oil Ceder Oil /deck oil, will stop colour change of wood, easy to apply. If you want a colour Jotun Demidekk (not cheap but lasts well) Just taken some old engine oil to the recycling centre - not the nicest smell, reminded me of an old VW Beetle I bought, it was 25 years old and had been wash under and inside every cavity with old engine oil, many times. It stank but zero rust any where. Not sure I would use on wood.