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Author Topic: GSHP Install - opinions please  (Read 18988 times)
marshman
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« on: September 21, 2015, 03:52:49 PM »

Been considering this for a while. 

House approx 240 sq m,  well insulated (12"+ insulation in loft, double glazed, cavity wall insulation) currently heated by woodburning boiler stove (14kW to water & 8kW to room) driving underfloor heating upstairs and downstairs. Surrounding land of approx 1 acre with good access. Woodburner burns any wood I can find - mainly old pallets.

Looking at changing system because a) woodburner is now 30 years old, b) its getting harder to get the wood and chop it up and c) it would be nice to put the heating on a timer so you don't come home to a cool house in the middle of winter.

Had an EPC done which laughingly quoted space heating requirement of 30546 kWh per year & 3772 kWh per year.

Rang round and got a whole range of quotes up to 30k but one local guy came round and seemed to talk sense his quote is as follows:

21157.50  for

5 ground loops (no slinkies but a total run of 1100m)   -  overdone because we are on a shingle bank and he is concerned ground conditions.

Thermia Diplomat Optimum G2 10 SP  heat pump with built in hot water tank    (predicted heat output 21163 kWh/year heat + 3300 kWh per year to water) SPF 3.97

120ltr buffer tank

Lowara inverter driven booster pump to increase hot and cold water pressure throughout the house

Powerflushing existing UFH ssytem

Includes commissioning and all electrical work.

Questions:

1. Does the price sound right?   - should be straight forward install as easy access to everything with little or no making good to do.

2. Buffer tank and hotwater tank don't seem very big to me. At present we have a massive 500 ltr tank which gets heated once every 2 or 3 days.

3. How reliable will the system be?  (current system is 30 years old and never (never!) given trouble - even got the same circulating pump - it's a simple system!). The pressure booster worries me for a start!

4. Is Thermia a "good" make of GSHP?

Biggest worry is the massive outlay and potential running costs approaching 1000 per year (electric cost) when at the moment the cost is almost 0 - well maybe 100 per year in electric for circulating pump and diesel getting & cutting the wood - my time is free Wink  Also there is the very real danger of the RHI being cut before it is commissioned.

Any info/opinions appreciated.

Roger




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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
Mostie
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« Reply #1 on: September 21, 2015, 04:32:22 PM »

Roger, I often wonder if something like this is too complicated for a domestic dwelling and the cost of a failed compressor may frighten you  faint
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todthedog
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« Reply #2 on: September 21, 2015, 04:47:55 PM »

What about a new wood burner a tad more efficient, buy in wood. I'm getting too old, and hate chainsawing.
Plus an ASHP, we have one which we use in the shoulder months just in the downstairs about 50m2. Instant heat.
Less fuss and a deal cheaper.
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JonG
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« Reply #3 on: September 21, 2015, 05:05:22 PM »

That price looks about right pretty much in line with what we would price at for a similar job, but we would offer the NIBE over the Thermia, better control interface, better UK back-up and we have had less issues with NIBE in comparison with Thermia/Danfoss.

NIBE would suggest a 200 litre buffer but it is designed to work differently to your existing system, given that it doesn't store as much energy, more to guarantee flow rate and flow volume and avoid short cycling.

We also fit the Lowara pumps which are very good, you need to keep on top of servicing and especially expansion vessel pressure and integrity.

If the RHI goes it would more than likely be next Spring so could easily be up and running before then?

A good install should last around 20 years but there will be repairs along the way inevitably due to the number of moving bits compared to your existing set up.
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dhaslam
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« Reply #4 on: September 21, 2015, 05:50:08 PM »

It does seem a little expensive  but  it takes the  away a lot of the work if that is what you want.     The way to keep cost down is to use off peak electricity as far as possible.    It helps if there is a a period of low cost daytime electricity  but  by using your existing tank as a buffer  as well as  the heat capacity  in the floor you should be able to minimize daytime electricity.   My electricity usage   for 2014 was  1278 kWh for the heat pump and  two circulation pumps. Practically all was at off peak rate.   I do use the woodstove as well and that covers about  50% of the heat requirement.  If I was starting again I would  use a non boiler stove  and  bigger heat pump because the stove costs ten times more to run.   

The heat pump you are considering seems to be only available in three phase and has built in immersion which needs to be used with caution.   With a budget of that size it might be better to  use two smaller heat pumps. Applying the  Linbergh rule means double  risk of  failure  with two  but  you would still have sufficient heat in most circumstances with one working while repairs are organized.

           
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brackwell
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« Reply #5 on: September 21, 2015, 06:19:08 PM »

Presuming you still have your PV then i would use that to power a ASHP via a Immersun programmed to switch a relay when excess leccy exists. A small unit will take a big load of the heating leaving a smaller more efficient wood fire to help with the worst.

The bigger question is how come your EPC threw up such a large heating requirement. Maybe you also need to address this also.

Ken
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marshman
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« Reply #6 on: September 21, 2015, 07:56:06 PM »

Roger, I often wonder if something like this is too complicated for a domestic dwelling and the cost of a failed compressor may frighten you  faint

I kind of wonder about this to which is why I am asking for peoples opinions.

What about a new wood burner a tad more efficient, buy in wood. I'm getting too old, and hate chainsawing.
Plus an ASHP, we have one which we use in the shoulder months just in the downstairs about 50m2. Instant heat.
Less fuss and a deal cheaper.

Again have thought about this, a newer more efficient woodburner is a plan "B", one concern is that the logs I can buy in have a lot less heat output than the pallet wood I currently burn - I know I've tried them. see below for comment on ASHP.

Presuming you still have your PV then i would use that to power a ASHP via a Immersun programmed to switch a relay when excess leccy exists. A small unit will take a big load of the heating leaving a smaller more efficient wood fire to help with the worst.

I did get a quote on a ASHP, the saving was not as great as I would have thought. I only got it for comparison. Not overly keen on them as we live right on the coast and I would be worried about corrosion. The only saving is on the ground loops as far as I know. They are not as efficient (though they are  not bad) and the RHI is a lot less. Yes I still have the PV and it's still going really well BUT it's output in the winter when you need the heating is not great - this is not helped by the shallow angle its mounted at. We don't need much heat on the still sunny days, its when the easterly wind gets up and down here that usually means cold and grey and the PV is doing a few hundred watts at best. The other issue with having a wood burner in tandem is the requirement for a heat meter which adds to the cost.

Thanks for the thoughts

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
marshman
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« Reply #7 on: September 21, 2015, 07:58:54 PM »

That price looks about right pretty much in line with what we would price at for a similar job, but we would offer the NIBE over the Thermia, better control interface, better UK back-up and we have had less issues with NIBE in comparison with Thermia/Danfoss.

NIBE would suggest a 200 litre buffer but it is designed to work differently to your existing system, given that it doesn't store as much energy, more to guarantee flow rate and flow volume and avoid short cycling.

We also fit the Lowara pumps which are very good, you need to keep on top of servicing and especially expansion vessel pressure and integrity.

If the RHI goes it would more than likely be next Spring so could easily be up and running before then?

A good install should last around 20 years but there will be repairs along the way inevitably due to the number of moving bits compared to your existing set up.

Thanks, are you saying the Thermia is less reliable?

Also is the Lowara pump necessary, why not stay with the unvented system - the tanks are already there so why complicate it? - its a question for my guy really but interested to hear other views.

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
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« Reply #8 on: September 21, 2015, 08:09:28 PM »


The bigger question is how come your EPC threw up such a large heating requirement. Maybe you also need to address this also.

Ken

Yes, initially not happy about that but its just a number!  It's a stupid quirk of the system. Its a very old property with very thick walls. It has been renovated and has an inner skin of 5" thermal blocks and a 2" filled cavity. However as the EPC guy could not see the blocks or the cavity he has assumed it is a solid wall. The house is also pretty large (240 sq m). I have been told that in a way it is good as the RHI is based on the figure quoted on the EPC and not on reality. As I said in my first post the existing wood boiler keeps the house toasty and in the coldest bits of the winter its going around  6 hours a day, so totally over estimating I get 6 x 20kWh x 180 days = 21000kWh - pretty close to what the estimate from the installer says - not the 30000 odd kWh per year stated in the EPC.

Once I've sorted the heating I will be replacing the windows - currently old wooden (rotten, but draughtproof) 16mm double glazed units with some triple glazed units which will help.

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
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« Reply #9 on: September 21, 2015, 09:10:57 PM »

Roger,

Is it correct that you estimate the electrical cost to run the GSHP at 1000/yr  ie x cop of 3.97 = 3970 worth of heat  ??

I agree a poor EPC is to your benefit if you are claiming RHI but of course the the installation then has to be MCS standard.  The MCS standard is calculated on virtually every room being maintained at 21C so it is easy to reduce your actual requirement below the EPC/MCS value.  I have forgotten now but do you need to have a EPC rating to claim RHI=could this be a problem?

I share your concern regarding ASHP corrosion-bad idea.

Does GSHP work in shingle?  I really dont know but i have some doubts.    If the tubes are packed in heat transmitting material perhaps but does heat travel down from the surface of shingle?

My philosophy is always to reduce the outputs first ie DG and the efficiency ie modern stove perhaps burning half the wood.

Ken
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gravelld
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« Reply #10 on: September 21, 2015, 09:43:03 PM »

Have you looked into reducing demand? It's all relative of course but I would not call your house "well insulated", it's about the bare acceptable minimum, and that's not talking about air tightness, thermal bridges (sounds like an unusual construction, is the cavity bridged much?) etc. Had a thermal imaging survey done? Can you insulate externally?
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JonG
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« Reply #11 on: September 21, 2015, 10:12:31 PM »

MCS Standard for a retro is 21 in living and dining, 18 in kitchen, hallways and landings and 22 in bathrooms.

There are differences between NIBE and Danfoss, in terms of the product and the companies. We are installers and service agents for both so have seen them from all sides.

Danfoss had a UK presence which was haemorrhaging cash, Danfoss pulled the plug and a family owned Irish firm (Ashgrove) bought the rights to market Thermia in the UK. They are rebuilding things slowly.

They have brought a better technical knowledge to the product but many installers had lost faith in the interim due to the collapse of the UK support. We have repaired many more Danfoss units than NIBE, but there is a caveat here. Danfoss UK and Ashgrove inherited a stack of 10 year warranty installs from the bad old days which in some cases resulted in premature failure, that said we have had to work on plenty of good installs that also have a high failure rate. Mainly, 3-ports, soft starts, circulators and sadly some compressors.

In all of our NIBE installs we have only had 1 soft start fail and a collapsed flexi on a ground loop circuit. NIBE also offer a 7 year warranty as standard, which you pay for as an option with the Thermia, this is supported by a network of NIBE service engineers, so if your installer is away or busy you still get support.

Performance is very similar, but the Thermia does not allow you to have a set point for HW, it works on a pressure stat on the fridge circuit that cuts out when the HW is at around 48-52 degrees, with the NIBE if you want less than this or higher you can make the choice and/or top it off with the immersion.

If you have a multifunction relay in your inverter you can link it direct to the NIBE and use it to bring it on for HW prep if there is excess generation, I am not aware that this is feasible on the Thermia, a MF relay is about 140 so much cheaper than an Immersun. This is also possible with an IDM unit if you fancy some Austrian bling instead. 

Thermia do have some interesting stuff in the pipeline though like an inverter driven single phase unit,they already have this in the 3-phase products but haven't reworked for 1 phase yet.

In terms of the cylinder you could stay with a vented option fed from header tanks, but you would need an up-sized coil sized to match the flow rate and heat output from the heat pump, but there is a fair chunk of wasted heat in a vented installation due to peculation of heat up the vent, you would also want it as close to the HP as possible to avoid distribution losses and flow rate issues across the coil.
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JonG
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« Reply #12 on: September 21, 2015, 10:31:03 PM »

Sorry meant to say that the cylinder would need 2 sensor pockets for a Thermia install too.

Our clients have experimented with E7 but due to the long run times on heat pumps they end up using too much higher rate leccy during the day which negates the benefit of the lower rate overnight.

If you have a non-RHI system with multiple options it may work OK , but the rules around metering and bivalents under the RHI make it difficult to design systems of this nature.

If you did decide to go ahead in a post RHI world, we would recommend ditching the ridiculous 100% sizing rule and go with a bivalent.
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marshman
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« Reply #13 on: September 21, 2015, 10:38:36 PM »

Roger,

Is it correct that you estimate the electrical cost to run the GSHP at 1000/yr  ie x cop of 3.97 = 3970 worth of heat  ??

I agree a poor EPC is to your benefit if you are claiming RHI but of course the the installation then has to be MCS standard.  The MCS standard is calculated on virtually every room being maintained at 21C so it is easy to reduce your actual requirement below the EPC/MCS value.  I have forgotten now but do you need to have a EPC rating to claim RHI=could this be a problem?

I share your concern regarding ASHP corrosion-bad idea.

Does GSHP work in shingle?  I really dont know but i have some doubts.    If the tubes are packed in heat transmitting material perhaps but does heat travel down from the surface of shingle?

My philosophy is always to reduce the outputs first ie DG and the efficiency ie modern stove perhaps burning half the wood.

Ken

Hi Ken,

I think so! the illustration quotes an energy use (i.e input) of around 6150 kWh per year.

Share your doubts about shingle and it's conductivity, however most of it is not "big" shingle it's more like wet dirty pea beach with strips of clay in places. It's difficult as the ground varies enormously from chunks of sold grey clay through dirty peabeach to clean free running shingle. Having said that we are not that much above the water table in fact in the winter the pipes will be mostly in the water table which I think could be a good thing.

Agree about reducing outputs first but the stupid RHI discourages this. You want a high number on the EPC to get maximum RHI (needed to pay for the inflated cost of the installation), then reduce the heat requirement after the installation to save on running costs. Having said that the MCS requirement makes the installation more expensive so in the end all that happens is my head explodes trying to work it all out!  The house has an EPC rating of D (59) according to the report and as it already has loft and cavity insulation as far as I know I am eligible for the RHI. You are correct about the requirement for sauna temperatures in all living rooms but the guy has done the calculations and has sized the heat pump accordingly - i.e. oversized. I suspect if I go ahead and the replace the windows as well the running costs will be a lot less than quoted.

It is not a clear cut decision by any means. Perhaps I should get another quote forgetting RHI and MCS etc and see what that runs out at.

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
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« Reply #14 on: September 21, 2015, 10:50:23 PM »

Have you looked into reducing demand? It's all relative of course but I would not call your house "well insulated", it's about the bare acceptable minimum, and that's not talking about air tightness, thermal bridges (sounds like an unusual construction, is the cavity bridged much?) etc. Had a thermal imaging survey done? Can you insulate externally?
The figures given are from the EPC - a box ticking exercise where if there isn't the right box you tick the nearest available one. The house has bits dating back to the late 1700's, its a big 5 bedroom detached house in a very exposed location.  It is well insulated, in excess of 12" of insulation in the loft, double glazed, draught proofed, Solid walls 18" thick, then a 2" filled cavity, then 5" thermal blocks inside that. Of course it can be improved but I at the moment I am trying to juggle EPC figures, RHI/MCS requirements and long term running costs and reliability.

I agree the house could be better but its been wet and windy here all day, no sun, and the outside temp is now down to around 11 deg C. Inside the house is still 20 deg C. No heating on - last time the fire was lit was yesterday for about 2 hours to heat the water. I know there is a lot of thermal mass but given the very exposed location its not that bad.

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
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