The Optimum domestic hot water and heating system

[willbish]

5 hours ago, JSHarris said:

Last week I had the bright idea that it should be possible to fit a duct cooler in the same place as the pre-filter, and as that's only a few feet from the ASHP,

 

This is interesting, @JSHarris could you elaborate a bit more please? I liked the idea of a brine geothermal heat exchanger for the MVHR but struggled to justify the additional cost. The idea of a duct cooler seems simpler and cheaper, would your ASHP be able to keep up with MVHR flow rates to provide the 12°C input air you mention?

 

 

[MikeSharp01]

5 hours ago, jack said:

 

Vented either means gravity (=low pressure) or thermal store (=less available hot

Nothing in the regs, I don't think, to prevent you using a high pressure cylinder and venting it with a 60 foot length of pipe straight up. Bit of an eyesore but 2 bar and no restrictions.

[Cpd]

5 hours ago, SteamyTea said:

So don't dismiss an ordinary system on a standard heat loss assumption, it can be easily overcome.

The very decrepit system in my house is a standard hot water tank with an immersion, cold water in the bottom. The house is uninsulated and the tank had just the foam on it..... I did some measurements of how much heat was being lost overnight and was terrified! I insulated that tank to within an inch of its life and then re did the calculations and the difference was astonishing. Due to trying to cut down on my electric bill even further I installed a pumped electric shower and a few wall worts above sinks, yes it’s total shite but we get by  and I was reducing my electricity consumption. Then I had kids and all that fluffing around trying to save a bit of cash went west..... way west. 

 

I am in in the early stages of needing to designing the new hot water and heating system for the cottage next door and will be following this thread and many others with interest, trying to learn all I can.  

[Jeremy Harris]

43 minutes ago, willbish said:

 

This is interesting, @JSHarris could you elaborate a bit more please? I liked the idea of a brine geothermal heat exchanger for the MVHR but struggled to justify the additional cost. The idea of a duct cooler seems simpler and cheaper, would your ASHP be able to keep up with MVHR flow rates to provide the 12°C input air you mention?

 

 

 

 

Tough to get any worthwhile geothermal heat in the UK, you need to drill down a few km, even in areas like Cornwall, where the prospect of getting some geothermal energy is reasonable, but even that hasn't really been shown to be worth the effort.  On a domestic scale, geothermal is really just a pipe dream, as the cost to get any worthwhile heat energy would run into many millions.

 

Using solar pre-heating, via a shallow ground heat exchanger is practical, and is the system used by most ground source heat pumps.  This isn't geothermal heat, it's just heat from the sun that's stored in the upper few metres of soil.

 

A duct cooler is essentially just a radiator-type heat exchanger, placed in the duct, or in a chamber with the duct connected either end, with cool or warm water pumped through the radiator in order to either cool or warm the air flowing through the duct.  There's no merit in using warm water on the intake side, as that reduces the efficiency of the heat recovery process in the MVHR, but for summer cooling there is an advantage in pre-cooling the air intake, as that will have a modest impact on cooling the house.

 

My plan is to do this cheaply, so I'm looking at radiators, rather than purpose made duct heat exchangers, as this unit will be mounted outside and can be quite large and custom made to fit whatever suitable radiator I can find (maybe one designed for a plinth heater).  I'll fit a motorised valve, so the cool water only flows through this radiator from the ASHP when cooling mode is selected from the room thermostat.  Water cooled by a buried pipe loop in the ground would work for cooling, as the once down below the top metre or two the soil will be around 8 deg C all year around, enough for summer cooling I think.

[joe90]

4 minutes ago, JSHarris said:

There's no merit in using warm water on the intake side, as that reduces the efficiency of the heat recovery process in the MVHR,

 

But, if you install it between the MVHR unit and the manifold on the intake side or in pipework for a particular room ( I did think of our bedroom, yes selfish but we are normally there on our own).

[Nickfromwales]

1 hour ago, MikeSharp01 said:

Nothing in the regs, I don't think, to prevent you using a high pressure cylinder and venting it with a 60 foot length of pipe straight up. Bit of an eyesore but 2 bar and no restrictions.

The things people suffering with sunstroke come out with can make you laugh !

[AliG]

7 hours ago, Mr Punter said:

 

 

What a cowboy.  This needs to be insulated to comply with building regs in England.  I can't imagine this being different in Scotland. 

 

I had been considering what to do about this. I did ask if it should be insulated before it was all covered up and he said that he didn't think so.

 

Of course I didn't check until I became suspicious about our high use of gas with the heating off, so only hot water.

 

The UFH manifold circuits are insulated, but not the hot water circuit. Having read more about it 19mm Armaflex would reduce the pipework heatloss by around 70%.

 

I am kicking myself that I didn't tell him just to do it, of course he should have known, I can perhaps put it down to not having installed a hot water circulation system before, but the system designers should have known. Also when I checked later I saw that the insulation is very cheap, so to insulate the roughly 60m of pipe would not have cost much at all, £150 for materials plus labour.

 

Much of the pipework goes down a main spine in the hall, maybe 2/3 of it. We could probably open this up relatively easily and insulate the pipe. My wife won't be pleased about the disruption as we are almost finished, but it looks like it needs to be done.

 

I have a FLIR thermal camera that attaches to my phone. I think I will have a look at the ceiling at the weekend and see if the pipes show up which will show the heatloss.

Edited July 10, 2018 by AliG

[Jeremy Harris]

The other point is that in summer that heat is just making the inside of the house warmer than it needs to be.  We had that problem when we had the combination thermal store, in summer the heat loss from it made the services room and the adjacent bedroom very hot indeed.

[willbish]

15 hours ago, JSHarris said:

I'm looking at radiators, rather than purpose made duct heat exchangers, as this unit will be mounted outside and can be quite large and custom made to fit whatever suitable radiator I can find (maybe one designed for a plinth heater).  I'll fit a motorised valve, so the cool water only flows through this radiator from the ASHP when cooling mode is selected from the room thermostat.

 

I would be very interested to follow your progress, please keep us updated.

 

I as alluding to Brine heat exchanger like @Barney12 has installed. Geothermal i think is an incorrect term.

 

Has anyone got something like this plumbed into their ASHP and MVHR unit and using it for cooling? Would the effects be that noticeable?