Posted by: @alexm

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Thanks Derek. Yes, in open ground the pipework should be 1.2m+ below the surface. We unfortunately can't get a long enough trench at those depths but do currently have more shallow trenches dug for our foundations. An insulated floor slab is going to be built off the foundations which might prevent the foundations from getting heated by the sun etc and so they might maintain a constant temperature even though they're not that deep in the ground.  

 

 

Good point about it being a heat exchanger. Yes, it will be combined with an ashp and ufh.

I suspect that the system would still work, but probably not as efficiently as if the pipes are installed further down. As Transparent pointed out, it will be dependent upon the amount of heat energy available, and how readily it can be replenished.

Thanks Derek and Transparent. Yeah, send like the bottom line is whether the foundations can hold and access heat like the ground can at 1.2m+ depth. I'm trying to figure out the precise difference between a heat pump and a heat exchanger... I guess an exchanger transfers heat whereas a heat pump magnifies it. Just wondering whether an exchanger will be able to add much heat to the inlet on the mvhr. Thanks again

Apologies for not appreciating the difference between a GSHP coil and one being used as a heat-exchanger.

Nonetheless, its efficiency is constrained by the surface area of the pipework and the ability of the surrounding medium to pass heat.

I use a concrete floor slab in one part of my house as a 'thermal store', heated hours in advance via ufh pipes, which in turn are heated by solar-thermal panels.
Its significant feature is this thermal lag. It takes a long time for the heat to pass throughout the concrete because it doesn't have high thermal-conduction.

That will also affect the pipe coils which @alexm is considering being buried within the foundation trench.

Whichever way they are to be used (heating or cooling), they will need to have a low flow-rate to slowly transfer heat to/fro concrete.

Personally I'd prefer to place the coils just beneath the concrete foundation rather than within it.
There they will at least be exposed to the underlying damp ground rather than only concrete.

NB you can't place the coils being buried any lower beneath the concrete strip because the Building Control inspector won't approve the construction of the foundation itself.
I'll explain more on this point if you want.

The issue I'm grappling with here is that you want to either heat or cool the air passing through your MVHR.

I have an MVHR unit in the loft... a self-install encouraged by a friendly Building Control officer! 🙂 

For the sake of others wanting to follow this part of the discussion, let me offer this diagram which shows the four ports for the pipework using different colours.

I've added a feature which increases the temperature of the airflow into the living areas, shown using yellow pipes.
But my modification doesn't offer any cooling effect in summer.

I've added a 150mm square radiator at the point where the heat-exchanger supplies air to that yellow pipe. It gets fed with water at 45degC from the nearest UFH manifold.
I've chosen the sort of radiator used for water-cooled PCs, available from the likes of Overclockers.

It's probably cost a let less than @alexm is preparing to spend.

Thanks Transparent. Interesting points. Sounds like the concrete in the foundations will act like an insulator rather than a heat sink. The plan is for the pipe to dispose of heat in the summer and draw the heat in the winter, hopefully turning the foundations into a thermal battery. I'm not sure if concrete is better than soil for this application or not. 

I like your ingenious mod on your mvhr using a computer heat sink plumbed into your central heating. Certainly cheaper than the proposal I'm looking at. The ComfoFond that we're considering does essentially the same as your heat sink (pre-heat the intake) but also cools it in the summer. Just whether it can do it sufficiently!

In general I would always expect 'soil' to be a better heat transfer material than concrete, if only because it contains water.
It's not just the high heat capacity, but that the water can move.

Even if there's no lateral flow of water within the site, it is still the case that warmer water will rise and cooler water will fall.
That allows gradual replenishment of the medium surrounding the pipe.

Hi, I'm Patricia Howard. I have a smallholding with two dwellings and several outbuildings, as well as 5 acres, in the South East, in Kent. My husband and I installed a Ground Source heat system in 2015 using a borehole as the water source, with multiple sources of professional advice (the borehold is dual purpose, as it provides irrigation water as well).

The first issue was that we had to have the borehole drilled three times to get a supply due to faults in drilling, not to a lack of groundwater. I learned more about drilling boreholes than I ever wanted to know in the process - one driller had to refund our money, and a second one had to drill twice, as they failed to line the first borehole properly. After a year or so, we started experiencing problems with water quality: in spite of the fact that we brought in two GSH experts and a Geotechnical company to design the system, we weren't forewarned about this. Due to the ingress of very fine clay particles, we have to flush our system (heat exchanger, pump) up to twice a week; we've had to replace the heat exchanger and the external Grundfos pump due to corrosion. Nowadays, people are advised NOT to use boreholes as water sources in areas with clay substrates. We have been told many times to consider installing a horizontal system to replace the borehole - but the costs of this are unmanageable now that we have the borehole, and we have found that, with persistent maintenance and some replacement of equipment, we can deal with the borehole water quality.

Our installation cost us about 3x as much as the RHI subsidy provided as, among other things, we had to mole underground to place the four-core pipework to bring the supply from our plant room into two buildings on our property. We have a 17th Century Grade II listed house, which we externally insulated (wood fibre) and where we replaced all windows and doors with double glazing. This was the only way to get ourselves off of fuel oil and propane and onto renewables. We also installed 100 solar panels, which subsidise our GSHP costs. Solar was the best investment we ever made! We have a wonderful result in that we have managed to conserve our Grade II listed buildings, bring them up to current insulation standards, eliminate radiators, and heat our buildings with a 40C heat source.

Since that time, we experienced few problems with our Vaillant GeoTherm 17kW GSHP itself - until recently. The GSHP has corroded badly internally, apparently due to problems that could have been foreseen - at least this has been learned in the past few years - such as oxygen ingress from the UFH pipes that we laid also in 2015. This problem is discussed in my recent post, as are the problems with Vaillant's supply of spare parts.

I look forward to participating in this forum. I think that it is vital for people to share their experiences and lessons learned, and to also get together to promote improvements in the renewables industry and keep it expanding.

@phowardstutterheim, welcome to the forums, and we’re looking forward to seeing you get your spare parts issue with Vaillant sorted out: https://renewableheatinghub.co.uk/forums/renewable-heating-grounds-source-heat-pump-gshps/lessons-no-spare-parts-for-vaillant-ground-source-heat-pumps-in-the-uk-major-corrosion-issue-is-another-problem-for-gshp#post-14295

Hi! 🖐️ Just had our heating overhauled a couple of weeks ago, replacing an ancient Camray 5 oil boiler with an 8kW Samsung Mono HT Quiet (AE080BXYDEG) and all new rads throughout — 8 up from 6. Mid-terrace, built 1900 — relatively leaky but improvements ongoing.

So far so good. We were without heat since October, with only portable heaters and immersion for water (£££££), so having our heating back feels like luxury.

I'm heavily invested in Home Assistant, so I'll be looking to get the heat pump integrated as soon as possible.

@Steven, welcome to the forums. Feel free to start a new topic relating to your heat pump, where you can share your experiences and performance.

hi all!

my name is ewan and i got a solar pv and ashp systems intalled about a year ago. i've got some issues with both and i'm planning on learning as much as i can about how everything works to try to sort them out.

i've been looking at messages on this site and i see there are great discussions going on. i'm hoping to get the help i need and happy to contribute when i know enough myself (but that may take a while 😉)

Hi Ewan and welcome.  I'm sure you know more than you think!  Please feel free to contribute and/or start your own thread if you have a specific question or problem.