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Author Topic: GSHP Install - opinions please  (Read 18973 times)
marshman
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« Reply #15 on: September 21, 2015, 10:54:32 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.

Thanks JonG for taking the time to explain still lots to think about and discuss with the potential installer.

The existing cylinder and manifolds for the UFH are all in the same small room where I want to site the heatpump so long pipe runs are not an issue.

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.
brackwell
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« Reply #16 on: September 22, 2015, 08:20:36 AM »

Roger,

You have been a long time member of this forum and therefore i am sure you have most of the issues in hand.

Standing back and looking at the big picture then i would say that if the RHI payments over the 7yrs meet the installation and running costs then what have you got to loose and you should go for it.  If after 7 yrs you do not like it, well so what dont use it.

Ken
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Bodidly
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« Reply #17 on: September 22, 2015, 08:51:09 AM »

From the maintenance point of view we are around 8 years in using a GSHP for DHW and part of the space heating with total maintenance costs to date being 0. One of the circulation pumps is getting a bit tired so that's 45 when I change it. Pretty good in my book.
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billi
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« Reply #18 on: September 22, 2015, 09:09:00 AM »

sure if it sums  up with the RHI ....., still  21000 GBP  is hefty  and  equivialent to   25000 kwh of pv units  per year
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Mostie
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« Reply #19 on: September 22, 2015, 12:52:01 PM »

.. and you can buy a 10kw ASHP for about a grand, at that price if it broke you could just get another, it wouldn't be worth getting someone to fix it.  stir
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titan
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« Reply #20 on: September 22, 2015, 02:10:18 PM »

I have just read through the whole thread and clearly you need to do the maths but I would have thought that an ASHP sized for your actual heating requirement instead of the ridiculous RHI requirements may work out more cost effective than an oversized system which will have to be installed by an MSC approved installer ( expensive). just to get the RHI. You say you are by the coast on shingle, unless it is permanently waterlogged I can't see that being very good as a ground array. However the proximity to the sea should give a frost free environment and probably be a good  location for a ASHP in the UK.
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marshman
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« Reply #21 on: December 12, 2015, 09:43:08 PM »

Thought I would post a brief update.

After much agonising, discussion, to'ing and fro'ing I went for it.

Basic spec of the system was similar to before:

10kW GSHP
120 ltr buffer tank driving existing underfloor heating
1200m gound loops
300 ltr DHW cylinder -  conventional vented system

Guy who installed it did listen to my concerns over the complexity of the original proposal and I am happy with the solution he installed.

Ground loops were put in at around 1.3 to 1.4m in the shingle (the trenching machine does not like shingle!) but luckily when we got to the back of the field we hit lovely wet clay and got the pipes down to 1.5m and into the water table. So I have just over 600m of the groundloops (about half of each of the four loops) in what I think are ideal conditions - wet clay.

The system was fired up for the first time on Thursday afternoon and has been running ever since. After deep and meaningful discussions about heatcurves and integral figures the initial heatcurve was set at 40 deg C. As we have a good underflooor system I have decided to leave it running 24/7 (i.e. heating is on all the time as it has such a slow response and the house is occupied most of the time. I can balance the flow round the underfloor loops to get an even temperature through out the house. Since then I have dropped the heatcurve to 38 degrees C because the house is simply too warm!  At the moment the pump is running for 20 minutes (using 2.4kW) in every 90 minutes - its around 11 degrees C outside (7 last night).  The house is still on the warm side so will see how it's doing in the morning and will back it off some more. but at the moment I am deeply, deeply  impressed. Heats the hot water up in around 20 mins to 55 degrees C, have made sure all auxilliary heaters are off! Have also installed an Apollo Gem PV power diverter to heat the hot water via the immersion when we have excess PV. 

The ground loops seem OK at the moment - incoming is sitting at 13 degrees C and out going drops to 7 or 8 degrees C, we will see what they are at the end of the heating season!

Some pics are attached.

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.
Iain
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« Reply #22 on: December 13, 2015, 08:38:30 AM »

Hi
You say you have dropped the temps for the heating.
I have my hot water cylinder set to 42 deg C (just a normal cylinder,boiler fed) This is quite hot enough for all we need.
So just wondering if the HW temp can come down a bit, without noticing.

Iain
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marshman
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« Reply #23 on: December 13, 2015, 10:12:58 AM »

Hi
You say you have dropped the temps for the heating.
I have my hot water cylinder set to 42 deg C (just a normal cylinder,boiler fed) This is quite hot enough for all we need.
So just wondering if the HW temp can come down a bit, without noticing.

Iain
Hi Iain, funny you should say that as this is exactly what I have now done. I have reduced the upper limit. Not as low as 42 though. The tank has two temperature sensors, one at the top and the other mid way down. It is the one midway down that triggers a heating cycle when the tank gets down to 41 deg C at the midway point.  The heat cycle will then run until the whole tank is up to the set temperature. It is this set temperature that I am reducing. There is also a weekly Legionella cycle where the tank is heated to 60 degres C. Never bothered about that before, we will see how it goes but I might delete that. When you say your temp is set to 42 deg C is that on the boiler or on a simple tank stat clamped to the side of the tank?

House still too warm this morning so heatcurve now down to 37 deg C and flow in the UFH loops adjusted again.

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.
Bodidly
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« Reply #24 on: December 13, 2015, 01:01:16 PM »

Slightly confused by your use of the term "heat curve".  I thought the heat curve was was the balance to how much the GSHP compensates for external changes in temperature. Is your heating system going up to 40C? Sounds hellishly hot for a well insulated building or is through rads and not UFH?
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titan
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« Reply #25 on: December 13, 2015, 01:40:00 PM »

I was wondering also about the term heat curve. The control on my GSHP is done via the return temperature setting which Kensa say is 5 deg C lower than the flow. It is currently set at 29 deg C so the flow is 34 deg C which is fine
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Iain
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« Reply #26 on: December 13, 2015, 01:54:32 PM »

Hi Roger

Quote
.When you say your temp is set to 42 deg C is that on the boiler or on a simple tank stat clamped to the side of the tank?

My boiler has an electronic temp sensor on the tank/cylinder, it cuts in at 40 deg C and cuts out at 42 degC. A lot more accurate than the mechanical thermostats normally fitted. I adjust the set temp on the boiler panel.

Iain
« Last Edit: December 13, 2015, 01:56:41 PM by Iain » Logged

1.98kWp PV (11 x Sharp 180 and SB 2.5)
20 x 65mm Thermal and 180ltr unvented
Powervault 4Kw - G200 Lithium-Ion (LiFePO4)
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marshman
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« Reply #27 on: December 13, 2015, 03:44:33 PM »

Slightly confused by your use of the term "heat curve".  I thought the heat curve was was the balance to how much the GSHP compensates for external changes in temperature. Is your heating system going up to 40C? Sounds hellishly hot for a well insulated building or is through rads and not UFH?

Sorry Titan/Bodidly I'm a bit new to heatpump terminology but trying to learn fast. The heatpump is a Thermia Diplomat Duo G2 10kW, (apparently similar to Danfoss), Yes the heatcurve as far as I can see is a curve which relates the maximum flow temperature (to the buffer tank and hence heating) to the outside temperature. According to the book of words a 40 degree heatcurve sets the flow at 40 deg C when the temperature outside is 0 degrees C. So if its warmer outside the maximum  flow temp will be less if it is colder then it will be more (up to a preset maximum). Thermia seem to base everything around the heatcurve. There is a Room Temp setting which effectively adds an offset to the curve, 3 degrees C on the curve for every 1 degree C increase in the Room Temp. setting.

The way the pump is operating at the moment when the buffer tank, and hence the water circulating in the UFH drops to around 25 deg C, it fires up and heats the water to what appears to be the temperature set by the heatcurve/current outside temperature (I think!). It then shuts off and sits there until the temperature in the buffer has dropped again. So at the moment it is coming on once for 15 to 20 minutes every 90 minutes or so.  I also think it looks at the rate of heat loss from the buffer tank to determine the current heat load of the house (and therefore the current indoor temperature) and varies the start temperature accordingly. Effectively you have to average out the temperature of the water circulating in the UFH, which I guess is averaging around 28 degrees C at the moment. So yes initially the temp of the water crirculating does hit 40 (or so) degrees C but rapidly drops (decays) to much lower temps. I am letting the system just run 24/7 (including the UFH circulating pump) and tweaking the temperature settings down every morning to allow it time to stabilise, the house has a lot of thermal mass, (huge inglenook and chimney stack and 2 foot thick walls),  when the house starts to get too cold I will know I have gone too far and can then step it back up one notch.

The attached pic is of the flow temp graph taken just after install. It shows the flow temp getting up to around 42/43 degrees C then dropping away down to 25 degrees C before another heat cycle. At that time the heatpump was running for 20 minutes in every hour.

Have attached another close up pic of the trenching machine - impressive bit of machinery. They said if it wasn't for the shingle they could have done all 4 x 300m loops in a day.

Roger



« Last Edit: December 13, 2015, 03:56:04 PM by marshman » Logged

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.
JonG
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« Reply #28 on: December 13, 2015, 04:56:55 PM »

The start time for the heat pump is via the value labelled Integral, which looks at the actual flow temp, required flow temp (as predicted by the curve) and the time elapsed between measurements.

As the integral drops at -60 it recruits the compressor at -600 it recruits the back-up source. As the actual flow approaches the required flow it climbs to 0 and the unit switches off.

Anti cycling is also built in in terms of start intervals.

The Danfoss /Thermia curve is built around a required FT at 0, more usually the FT is set to match the design criteria whatever that may be (i.e. -3 or -4 around here).

Ideally a room unit measures internal temp and adjusts the curve in line with internal ambient, otherwise on a cold windless day the curve may be higher than it needs to be because heat loss is lower.
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Bodidly
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« Reply #29 on: December 13, 2015, 05:25:05 PM »

No need to apologise Roger just interested as I was never quite sure myself what a heat curve is. Got a quick talk through on ours when commissioned and not really done much to it since setting it up as the darn thing is far smarter than me. Ours is set to a heat curve of 1.5 (whatever that means) and this is tied to the weather compensation software. Basically once we got the heat curve right the house stays at a steady temperature not from guidance from an internal thermostat but from the external temp gauge. Apparently running it this way is more efficient but don't ask me why just what I was told Cheesy

Hope your setup works as well as ours has. You sound like you have ample ground loops which should keep you well supplied with lots of cheap trouble free heat.
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