JohnMo

Main differences I see Brendon is actually using a modulating ASHP, trying to simulate real conditions, and controlling heat absorption rates within the simulated house. This goes a long way to represent real life conditions of wanting your house a set temperature. The Kiwa is testing with electric immersion heaters, and seems not to report or include output monitoring or compensation. As you say

If you are not after hot water on demand from the boiler, no need for a combi. If you are just doing central heating any suitably sized system gas boiler will do, you may be better having it as a pressurised system, just to keep air out and therefore less corrosion build up. Will be a simple system.

Auto balancing actuator is there to do one thing. Maintain a set delta T on the loop it is attached too. If flow temp is below 30 degs, it maintains 4 degs over 30 it maintains 7 deg delta T. As zones open and close, this delta is sometimes lost, the actuator open or close to ensure the delta T doesn't change. They don't care or know what they are attached too.

Not sure it does say a different conclusion, but that report is now very old and only really applied to fix speed heat pumps. Report are written early 2000s when most heat pumps didn't modulate. Recommendations states - for Installers Buffer tanks are unlikely to be required when the heat pump can modulate (i.e. if the heat pump is not fixed speed). 3 configurations of buffer, one a 4 port, the other 2 are actually not buffers but used as a volumiser in either the flow or return piping, so no mixing occured between flow and return water. Fig 41 shows a lower return temp for all test when no buffer was installed. Fig 42 shows a long on time time for all buffers, especially so for those in volumiser format. This really is showing the volume of the water system to be inadequate for the kW input. But a volumiser being better than a buffer to combat limited water. Fig 43 clearly shows if you split your system in small zones you do need an extra volume of water. But why not save money by not splitting in small parts? Fig 45, 46 47, when hysterisis was at 10, the highest CoP was in a no buffer configuration. Fig 48 shows by just running one rad with no buffer, you are running low on system water capacity But generally the report shows how much heat pumps have moved on in the last 20 years, they were cops of less than 3.

https://renewableheatinghub.co.uk/how-to-correctly-install-heat-pumps-so-that-they-work-properly-and-efficiently

Basically a buffer and LLH are the same thing, a buffer just has more capacity, both give hydraulic sepereration between the the heat source(s) and heating system. Both add inefficiency to a system; if added to a system that can be run without them being added. Managing zone size, can in most case delete any requirements, in a domestic situation, for a buffer or LLH. Saving capital costs and adding simplicity and efficiency. No LLH or buffer, less thermostats and zone valves, easier system balancing

Most if not all Viessmann products are designed to run weather compensation via their own controllers, and can run two zones at different flow temps if required via a fully open system without thermostats or trvs. So why mess with that? By putting a third party thermostat that will give less control or worse efficiency. Run as the Germans intended

Because they give a set delta T, they auto balance the system as and when actuators open and close, so a loop always has a set delta T. In this situation @Adsibob is supplying too much energy in to a loop and the way to balance this, is to increase delta T over the loop, so the mean flow temperature reduces

You don't need to do anything complex. For the rooms that overshoot 0.4 - do nothing for now. For the 1.9 overshoot you are putting too much energy in the floor. Reduce that loops flow rate by 0.5L/min. Monitor and adjust as required. Less flow less energy, more flow more energy, adjust at the loop flow meters. Auto balance actuators will not help with this. Once your room over shoots are all roughly the same, reduce flow temp a degree at a time. If you hot water and CH are set at different flow temps you can reduce the flow temp to CH at the boiler.

Not many users on the database. Not surprising when they want £600 for a monitoring kits.

Dump the zones go single zone, balance the flow rates to equalise the heat dumped in to room. Gas boilers are usually way to big and struggle on low heat demands.

How do you model the radiator DT, with a variable temperature system, as DT would continually be changing in the WC system. I know on my boiler that if I set the flow temp at 30 degrees the pump will be modulated to manage a DT of 4, if I increase the flow temp to 70 the pump flow rate is managed to give a DT of around 20. Your DT is only really fixed at a set design temperature, form then on it moves, based on flow temp and room temp, the closer the room temp gets to radiator temp the less work the radiator does so the DT changes.

Or a volumiser, in the flow or return piping, then there is no mixing of the flow and return water. Or if installing a buffer install as a 2 port buffer between the flow and return, so its only engaged as zones close off. Or stop zoning everything in to small areas/water volumes. A recent test (simulation) was showing a reduction of 1 on CoP, with buffer compared to without buffer. Both running WC, but with buffer HP required increased HP flow temps to overcome the mixing within the buffer. If your are getting a couple of batches of cheap electric, a large buffer could be beneficial even with the hit in CoP. But you would need a low energy consumption house to make a real benefit or a very large buffer.

But then your CoP takes a hit

That's a good piece of work Think UFH curve is just 1 for 1 instead of 1.3 Just plotted outside temp from -10 to 20 in one column and the formula next column Added my WC curve to your spreadsheet and due to lower flow temps of UFH ended up with a projected CoP of 4.82 on WC, but the savings against a fix flow temp were low only 5%. CoP changes to 4.59.

that subject to not being so large it ends up cycling to much. we are on 300mm centres and loop lengths matched to the heat loss of the room. 16mm tube max length used is 100m. To date we have not had to flow any warmer than 34 degs even at -9 outside temp. We have Ivar manifold and mixer. Did have actuators, then Salus self balancing, now they have all be removed and run a open system on a single zone. Soon to install a 6kW pump, heating house and summer house. The thing with UFH is your house doesn't need to be hot to feel comfortable. Our is rarely above 19 deg unless the wood stove is on or we get solar gain. Glycol would only be needed for a heat pump, or anti freeze valves in leu of glycol

Good idea So just form standalone walls within walls, should be easy enough to do and zero strain on anything

So been reading up. A log building like this can grow and shrink quite a bit. Any battens directly screwed to the logs can place a restriction on this action and lead to splits and cracks. The normal way it seems to attach at batten is to use an angle bracket, this attached to the batten with two screws and to log with a single screw in a slot within the bracket, this allows the building to grow or shrink without effecting the internal wall. The internal wall stops about 50mm short of full height and skirt is formed from the ceiling to cover the gap, as a sliding panel. So my thoughts are a variation on @Iceverge suggestion. Wrap the internal walls in a breather membrane. Then attach 100mm battens at 600mm centres via sliding brackets to the logs. Stop 50mm short of full height. Full fill with rockwool or similar up to roof. VCL fully taped on walls and ceiling. Roof external 100mm PIR. How does that sound?

Interested - So what inputs did you use to get your data points?

That's huge, you will need an intercom system to speak to anyone. We have 3 large bedrooms and 3 bathrooms in the same space. I assume your loo will become the accessibility toilet sink ect, but sounds to small at 3m2. Seems at lot of house for just 2 bedrooms?

Are your calculations allowing for glycol or no glycol in the water mix. This could 10-15% of energy meter reading.

Why would you use a liquid DPM for a new build. Your DPM isn't for airtightness it's to stop ground water transfer in to the building structure.

To many variables to comment on, the house may be huge, the heat pump huge, setting everything at high temps, loads of zones, heat pump cycling, poorly commissioned. Do the same with gshp you would get a similar outcome. PV in winter output is the just about zero anyway, so will have little or bearing on monthly heating bills. Many on here get excellent cost effective heating from an ASHP. Mostly down to how you set things up and operate, keeping flow temps as low as practical.

So what flow temp is the ASHP using to achieve a cylinder temp of 51 in 45 mins. Assume must have a big heating coil. Flow temp 65, CoP close to 1.2 60, CoP close to 2.5 55 cop CoP close to 3 All the above are on a 5 deg day. Depending how many times you heat the cylinder in a day, could have a marked influence on your electric consumption.

Only thing I would say about 35mm battens, with plumbing is there may not be enough room for pipe clips.