SteamyTea

You are not building a block of flats, the fire issue was caused by a number of failings, not just one.

Not necessarily. It really comes down to how variable the weather is. It could work out cheaper if you do not have to 'overheat' to get the temperature you want later. An ASHP works best when it is doing the least work.

I did not include MVHR in my calcs. Just trying a basic model out and I tend to see how close it gets to my actual data collection.

Can you reduce that. Try it at 32°C.

I think the trick is to get both right at the start of the design stage. Then it is relatively easy to do the rest. The one thing that is hard to model is the effect of windwashing. A stiff SW wind is generally warm, but even a relatively slow NE is anything but. I may try and incorporate some solar gain and wind effects later. The trouble with even a basic model is verifying it against real data. I can make just about any model fit existing data, not so easy the other way around.

Using min OAT and adding a bit to allow the temperature to change is probably good enough. I was, just because I was up early and bored, knocked up a very basic calculator. The thermal losses via ventilation dominated.

A slightly left field look at this, and in no way am I suggesting this can be done safely, but: As the boiler usually has water circulating around it, which limits the temperature (until it boils and can release hundreds of times the energy), would it not be possible to pump air though it instead. It may need a relatively high pressure pump to give a decent mass flow rate, which needs to be at least 4 times the usual water mass flow rate, and probably 12 to 15 times in reality as you don't need air coming out at 80°C. Then that warm air can be piped to where it is needed. This dose run a risk of filling the house with smoke, or worse, carbon monoxide, if the boiler jacket leaks. So I would not try it. Probably much better to get a Honda Generator and run an Air to Air heat pump from it.

No, you need to use the minimum OAT that the Met Office supply, and preferably the daily data not the monthly data. https://catalogue.ceda.ac.uk/uuid/b37382e8c1e74b849831a5fa13afdcae I think soil temperatures are buried in there as well. To give you an example, my Feb (coldest month) temperatures have a mean of 4.3°C, but a minimum of -0.8°C (the whole month, in 1986) Is this just the footprint of your house, or the total floor area, or even the total liveable area? Just thinking that @joe90's place is about 200m2 and his HP is 4 kW, and that does his DHW as well (I know that we are in the very mild SW, but you are not so different being on the west side of Scotland (Isle of Sky climate is very similar to Cornwall, within a degree).

Assuming ground floor, UFH can loose more energy to the ground, which generally has a lower temperature for longer parts of the year. On a second floor, it should realistically make no difference. If by you mean mechanical ventilation and heat recovery, then no practical difference as that is to do with air changes and not the losses though the walls, floors, roof, windows, doors etc. Depends on the view and if you are an artist. If the thermal losses are manageable, then no problem. Near me is a small cove, if a house has a south view, it would be of industrially scarred land, but the north view is of the Atlantic.

What happens if the cylinder is not up to the desired temperature after 30 minutes, does it totally isolate from the rest of the system. And was the system working correctly before the Nest was fitted?

It may make the numbers worse as the surface area to volume ratio is 6/a. Basically large houses have a better kWh/(y.m2) number than smaller ones. But then I think using the mean air temperature is wrong. There will be no excess heating for a large proportion of the year. I think this has to be modelled on a weekly basis, the MET Office probably has better data. I use a daily mean air temperature of 10°C as the point where I need to turn on or off my heating, using your number of 9.4°C would mean I have the heating on all the time.

From my understanding, condensing boilers are more like turbocharged cars. They reclaim some of the energy that usually goes to waste. If you run a turbocharged car at too low an engine speed, it is basically 'running rich' as there is not enough air to burn all the fuel. A similar thing can happen at the top end as the fuel injection system tries to put in more fuel, but the turbo has 'run out of puff'. So there is a sweet spot where all the fuel gets burnt, and maximum torque is produced. Now a boiler is obviously not the same as a TDi. Rather than having a 'rev range' is has a thermal range. This is just a range of temperature differences where the boiler can transfer the most energy for the least fuel. This is easier as a formula: Q = U×A×ΔT where, U is the overall heat transfer coefficient A is the overall heat transfer surface area and ΔT is the mean temperature difference between hot and cold side The trouble is that the cold side i.e. the water is not a constant, it varies, and as it varies in temperature i.e. gets hotter, the coefficient U would have to changes to keep the efficiency the same. As a rule, the flame temperature will be constant (within 10°C or so), A, the area of the heat exchanger within the boiler will stay constant, so all that can be changed is the temperature difference ΔT. As heating is not a linear process but follows an exponential curve: T(t) =1- t- exp(-k * t) Where T is temperature, t is time and k is a constant. This produces a chart that shows that when there is a large temperature difference i.e. cold store, the energy transfer is large, but as the store warms up, the energy transfer decreases, even though the fuel burnt per unit time, is the same. Or in simpler language, the hotter you get, the more fuel you burn. The trick there is to find a lower bound temperature that satisfies your hot water needs i.e. 40°C and an upper bound for safety i.e 60°C Using the made up chart below you can find out the amount of time the boiler needs to run at (bare in mind this is showing % change, not absolute temperature). So what you need to find is the range where the boiler is condensing, the water never goes below an acceptable temperature, and never goes above a safe temperature. And runs for the least amount of time, as I think oil boilers do not modulate (I may be wrong here, but the physics is basically the same, just another variable in the mix). I have highlighted this with coloured lines. So for the same temperature change between the blue lines is 7 times units, and between the yellow lines is 22 time units.

It will be in the wording if the deal somewhere I am sure. Their compliance lawyer will have checked. So just change. There are plenty of others that are about to go pop. Or, phone 0161 836 1346 You and yours likes this sort of thing. I think Tuesdays are 'energy day'.

nO eXiT fEe. So free to change. If an offer is too good to be true, it probably is. Why I avoid all this swapping nonsense in a mature marketplace.

I find all this very interesting. I like logging data, and analysing it even more.

Having made air filter, you are going to need a very large area to reduce VOCs, they are not removed the same way as dust. So maybe a sensor and a flap. In fact, cant you fit an ordinary spring loads flap the wrong way around. Though it may rattle a bit if the spring is not strong enough.

You could get a cheap PlantPower particulate sensor, stick it into the MVHR input pipe, then with a bit of code, set a limit for it to turn the MVHR off.

About 10m of trench for every kW So 300m long Trenches can not be tightly packed, so say a 2 m gap between them. and they are about 1 m wide, that area becomes ~ 1000m2 Or about the same as PV (ish). This is not surprising as GSHP are really solar powered, just that the ground is buffering the annual solar input.

And now the area of an ASHP. Or shall we call it no more than 1.5m2

Me too, but it is alright, as I live right by the 3rd word polluted road of 2017/8. I would love to see the time serious data as there is no gas, so possibly it is all the people who burn coal and timber that is the real problem, not people with EURO4,5,6 cars (I missed the opportunity to work on the project a decade ago).

When I was working all this stuff out, I made my own spreadsheet. Seemed to work. Would be interesting to make up a calculator for working out UFH piping, then compare it to LoopCad.

Of dry timber, not sure if the FC table is for that. And just for a giggle, work out the area of land needed, with PV on it, to supply the same energy at the same time of year.

Possibly it. It may be hard to convince people that after being told they need everything less powerful i.e. vacuum cleaners, light builds, kettles, cars; to save the environment, to then come along and say, 'well actually, you need a 10 kW system, so we are fitting a 15 kW one. I think it is up to the manufactures to get this message across, and offer a scaleable system i.e. 4kW increments.

Only on new builds. It does not change existing installations as far as I know.

There is going to be no choice in a few years. https://www.gov.uk/government/speeches/spring-statement-2019-philip-hammonds-speech Still, your old plumber can service old boilers.