Beelbeebub

Grant have a schematic in one of their manuals for a hybrid. It's a pretty simple tee into the flow and return with NRVs to stop back flow (as you mentioned) The HP has a pump fitted already. In the case of the grant units, it's pretty powerful. With a 12 or 10m head (depending on model) vs the usual 6m or even 5m max heads in most normal pumps, so there is some. Leeway for extra pressure to drive the higher flows. But yes, flow might be an issue in some cases where microbore or just plain crappy plumbing is involved. Micro bore has been used successfully with HPs. A common way for MB to be plumbed was via a 22mm manifold in the floor/ceiling and only MB drops/risers to to individual rads. This means the MB only has to support the flow required to each radiator and an 8mm microbore can provide 750w typically with a HP. 10mm is 1kw With the advent of antifreeze valves you no longer need to use glycol and can get away with regular water plus some inhibitor/biocide (basically compatible with boilers).

Resistanc e heating is the cheapest capital expenditure system. And right now it's lower carbon than gas boilers The only problem is electricity is bloody expensive compared to gas (at least in the UK) If we had fusion or whatever magic "too cheap to meter" electricity generation system then we'd all be using resistance heaters. The French, with their nuclear fleet, were pretty big into it. But for now HPs are the way forward, mainly because they drastically reduce the amount of renewable generation we need to build out

The 60% refers to time using HP rather than boiler. The Gov report estimated carbon savings for *continuous hearing* to be 55% ie better than my quick calculation. It is true that 2x a day heating causes those savings to drop drastically. There is a really simple solution to that. Remove the heating timer (and provide an instruction leaflet explain why it's gone) I've been removing timers from our boilers (we get simple wireless thermostats fitted) for ages simply because one of the biggest causes of "my heating isn't coming on" is always the timer being poorly set. Either the time has shifted due to summer/winter time. Or simply drifted or the schedule itself being badly set. You could make removing the (heating) timer part of the install, the boiler is going to be controlled by the new control box anyway. All the boiler has to do is turn on or off at either the DHW temp or the heating temp (or a single temp in a very dumb system)

On that point. Estimates vary for how much of the demand a hybrid HP would take. In the better case it's 80% (occupant uses heating system correctly) In the worst it's more like 20% (occupant uses it like a gas boiler ie long periods off, short high power spikes) Say the average is 60% A HP coukd be expected to get a scop of at least 3 of not more (remember it does t give to operate in the coldest periods or do high temps which is where the hit to scop is). And let's say the average carbon per kwh for the periods the HP operates is 215g/kwh. It's probably lower as the average is lower but I have assumed the HP is operating more often during periods when carbon intensity is higher. So the carbon intensity of 40% of hearing is 1/3 that if a gas boiler... So overall carbon is about 72% that of a boiler alone. Let's say 1/4 of co2 saved. For a fairly easy, zero risk technical solution. Not nothing. Plus we are getting people used to HPs. Their gas boilers won't last forever. Typically about 10 years before they start to get a bit iffy. 15 years is when thry start to really play up. At that point you could upgrade the rest of the system (DHW). Maybe even just stick a 2nd 5kw unit next to the old one and then you have a 10kw system with really good modulation, redundancy and probably better defrost (can defrost alternately)

Though the problem is that it's hard to make HPs "pay for themselves" when the price differential between gas and electric is near 1:4. That said a hybrid system should have an easier job as it can only run when the conditions are such that it can get a CoP of greater than 4:1 and the rest of the time just use gas as per normal. But in carbon terms HPs soundly thump gas boilers. A gas boiler is a bit over 200g per kwh at best Our grid currently provides better than 300g per kwh, often below 200g ie the pout at which direct electric heating is greener than gas boilers. Even *at worst* a HP only has to get to a cop of 1.5 to beat a gas boiler in carbon terms. Pretty much any HP can beat that.

True enough

Yeah, commissioning is everything. That said, if the "kit" is just a HP, 2 NRVs and a controller box that either turns the HP or the boiler on depending on what's best. There isn't much to eff up. In the worst case the HP is rarely turned on, in which case the running cost will be no more than if the hybrid system was never fitted. Obviously the customer is out for the cost of the installation (though if most of that was covered they wouldn't even be out for that). Grant harvesting is always going to be an issue tho

I rent out an old stone cottage. The previous occupant always complained it was cold and damp and cost a fortune to heat. The new tenants say it is surprisingly warm and dry. Now. I did do some upgrades but the biggest thing is how they hear the place. Old tenant was out a lot so would turn the heating off, then come home at 7, turn it on for a few hours so it would run flat out and warm up a degree or two becaue of the massive walls. It would thnr go off overnight and repeat in the morning. It occilated between 12 and 15C and so was humid as well. New tenants work from home alot so leave the heating at 20. Turns off overnight where it drops to 18C then climbs again in the morning. They pay a little bit more as the losses are more but they ah e a warm dry house.

I'd say it's a good thing. The most basic hybrid system just tees the HP into where the boiler F/R pipes with some non-return valves. A control box to fire either the HP or the boiler is then needed. All you need is the HP, probably only a small model 5kw or so. No other changes needed. Boiler handles the DHW via existing cylinder or combi. From a customer perspective there is no risk of the system costing more to run than the gas boiler or performing worse than the gas boiler as their existing system is still in place. If their rads are undersized so the gas boiler has to kick in at a higher temp then they are still saving money, albeit less than they would otherwise. It then creates an incentive - "oh if you swap out these 3 rads, your HP can run more days". They do that and they use less gas. Thry upgrade a few more, maybe a bit more insulation and then the boiler fires only a few times a year. One day it does and they decide to spend the money of the last few rads and a new cylinder and there we go a heatpump house. The onky down side is the capital cost. Appropriate HPs can be a few grand. But if there was a (say) £3.5k grant it coukd end up being nearly free. The remaining 4k could be for the DHW switch if needed. You coukd even imagine the scheme buying back the smaller 4/5/6 kw units with a few years on them when you exchange for the "final" 8/9/10kw units. Then reselling them at a discount for incoming "hybrid" switches.

You mentioned a buffer. Is this a 4 pipe setup? Ie the HP fills a tank and then the UFH pulls water from the tank via it's own pump and blending valve? Grant often set their HPs up as if they are gas/oil boilers. In this case it might be set up to fill the buffer tank to a set temp. Check parameter 21-00. If that is set to 0 your heating temp is fixed. 21-01 gives that fixed heating temp, at a guess 40C If you want it hotter you can change it, but you probably shouldn't put water much hotter than 40C through a UFH setup anyway as you can risk overheating the slab and causing damage.

Can I clear up.... The graph says "underfloor flow". Is it of the flow into your UFH or is it the flow out from your HP? Ie was the 8-12 run getting to 50C a DHW run whilst the midnight to 6am run was for your UFH? Or were they both UFH runs? I assume the first was a DHW run in the basis that 5oC is way to hot for UFH! 😁 So some notes The DHW run seems to have some sort of defrost cycle, the little dropouts? Or are they something else? Secondly the UFH run, whilst it has defrost cycles - it doesn't look like those are the limiting factor in the temp output. It looks like the unit is modulating the temp output (the little wiggles) between the defrost dropouts. On that basis I would say your UFH cycle is being controlled to a set temp (40C at a guess) and that is why you aren't getting higher temps.

I think that is not something that can be changed, it's a readout of a machine parameter calculated from other parameters eg outside temperature. The parameters nearby are things like outside air temp, compressor rpm etc. Check 01-02 discharge temp 01-08 suction temp My gut feel is the suction temp will be near or even below zero for your heating runs but not quite as low for your DHW (defrost temp might also be lower).

Is the coil actually getting iced up? The remote display shows the defrost temp (parameter 01-05) Of you are running the unit hard to get mazimum heat into slab at night the deltaT between outside air and the refrigerant evaporation temp will be larger than normal so the outside temp at which the outside coil goes below zero will be higher. A higher outside temp also means more moisture so even faster icing. Hot water cycle will have a higher output temp and a lower power requirement which might mean the delta T between outside air and evaporation temp is smaller. Basically it might be that your could is getting colder providing 10kw at 35C than 8kw at 45C (figures for example) It's possible you may get better performance by not driving so hard?

When the heating comes on, does the flow pipe out of the HP get warm? You are saying that when the heating comes on, only 2 of your rads gets warm but then the HP shuts itself down even though there is a call for heat. That does sound alot like you're not getting the right flow on the heating circuit. Maybe try this First I assume you have a single 3 port valve that sends the water to the heating or DHW circuit. Remove the power head from the valve. This is easy, you need to isolate the supply then take the cover off thr case (single screw) once inside carefully undo the two screws on opposite corners thwt hold it down and it pops off. Replace the cover and leave safely tucked away. Use a pair of pliers or small spanner to old the shaft in the DHW position Set the system to heat the hot water, the HP should hum away merrily and the flow pipe should get hot and thecpipe to the cylinder. Once that's ticking along nicely use the spanner to switch the valve to heating. The pipe tonthrntqfiatoranshoukd start to get warm pretty quick. If the system then shuts down, your problem is some sort of flow restriction on the heating circuit. Maybe your rads have been turned down on the balancing vlaves. If it keeps running an all your rads get plenty hot, then yous system is hydraulicly OK and the issue might be with the controls, a parameter in the settings or an iffy connection. Alternatively get a local plumber to fit a visual flow indicator so you can see the flow rates.

Shocked, I tell you! SHOCKED!

This may be a case of not seeing the overall efficency wood for the (CoP) trees. At these mild temps the parasitic losses of the system (controls, valves, pumps) will be significant in comparison to the useful heat produced. October used around 200kwh for heat and DHW, which is about 275w continuously. That's a pretty low consumption given your standby consumption is likely to be in the 100w range. Maybe, in mild weather, some sort of scheduling where you turn the thing off might yield better results, but your finial gains are likely to be negligible.

https://www.carbonbrief.org/factcheck-18-misleading-myths-about-heat-pumps/

Is there an isolation valve(s) that was turned off during the building work? Sounds a bit like the heating circuit isn't able to dump enough heat and the HP is shutting down. If you could get a flow indicator fitted it would be helpful.

A2a has a theoretical advantage as the target temperature (and hence pressure) for the compressor to reach can be lower than with a water based system *for a given emitter surface area*. A2W can gain an advantage if it uses underfloor as the surface area can be huge. I think a2a has potential as it can usually be fitted alongside any existing heating system. This negates any fear of "will I be cold" or "will it cost more to run" as the owner can use whichever system is most appropriate at the time. They tend to be cheaper to install too.

The pumps aren't DC in any real sense. They are variable frequency AC, created by an inverter chopping up DC. Chopping up DC created from rectifying AC is no major problem. 240v AC is a a useful "universal" form of power - you power wall will output it efficiently, and your HP will accept it readily. Your electrician will be able to work with it and components like breakers, monitors, switches etc are easily availble. I doubt the efficency gains (if any) would be worth the extra hassle of a non standard setup.

Creativity isn't my problem. It's the restrictions. They, in turn add cost. I have a nice cladding system i am trialing on an out of the way building. No way I would be allowed to fit it to my main buildings because of planning restrictions combined with it's industrial look Personally,, I think there is a pint when how warm and cheap to run a building is for the occupants trumps how it looks for the passers by. But my view is very much in the minority, so solid walls and single glazed windows it is.

The thing is, I don't think it requires any creative or novel engineering. The major hurdles are finance and regulations (sound, visual etc)

That was the doc I was trying to remember. I think my error was I was focused on the older housing as that is where my professional interest lies as I manage rental properties, most of which are victorian or early 1900's vintage. My main interest in. HPs is because I can see I am goi g to have to deal with the upgrades in the future and am trying to work out how to approach it.

The house we just moved into is fairly well insulated and has good heat recovery system though it is stupidly big which pushes up the demand. My old self build had a demand of around 3kw at -5C and was stupidly easy to heat. I don't think the heating has come on yet (my parent now live there) Both are still on gas as the boilers are trucking along nicely and no point in chucking them out. My old house will be very easy to convert as I designed it to use a HP. The new one (my parents) will be a pig as the UFH has packed up and it's massive so the HP will cost more than ideal. Both will get swapped when they die.

I think the average is closer to 11kw, but yes a bare HP for a typical house can be had for as little as £2k but more likely £4k. But the point holds that a bigger unit will cost more than a smaller unit. Then you also have a higher likelihood of having to upgrade pipes, emitters etc. at extra cost.