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Author Topic: GSHP Install - opinions please  (Read 18903 times)
titan
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« Reply #30 on: December 13, 2015, 05:55:11 PM »

From the other posts it looks like the heat curve is actually some form of weather compensation.My unit has this but it is not used, Kensa say the response is too slow with UFH but OK with rads. Any increase in the flow temperature above 35 will drop the COP.
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Bodidly
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« Reply #31 on: December 13, 2015, 06:04:31 PM »

From the other posts it looks like the heat curve is actually some form of weather compensation.My unit has this but it is not used, Kensa say the response is too slow with UFH but OK with rads. Any increase in the flow temperature above 35 will drop the COP.

Strange they think it would be to slow. Thought it was devised to give the system time to anticipate a potential change in internal temps before they happen. Certainly works for us but we have IVT unit so maybe different brands behave differently.
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marshman
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« Reply #32 on: December 13, 2015, 09:52:23 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.

That is what I'm hoping for my system, will gradual tweak it over the coming weeks and see how it performs. The UFH does respond slowly but with the thermal mass of the house I think the weather/outside temp. compensation should work.

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 #33 on: December 13, 2015, 10:04:06 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.


Thanks Jon , That's what I was attempting to say Smiley

I did think that there should be some internal temp sensor not only to compensate for wind/rain etc but also changes in occupancy.  At the moment there are four people in the house but over Christmas there will be up to 9 (possibly 11) plus Xmas cooking which has to have a big effect. Will be interesting to see if my theory that the heatpump controller senses the heatload by the rate of heat extraction from the buffer tank.

I need to ask the installer about the possibility of a room sensor - other than the one connected to the largely redundant programmer (set to continuous at the moment). Also I have seen mention of "Tarif Control" which I assume means settings to take advantage of economy 7 - however can't find it in any of the menus - service or user.

Also would like to know more about the Brine flow and return temps and temp differentials.  Mine is incoming at about 13 degrees C and out at 8 or 7 degrees C which is a drop of 5 or 6 degrees which seems a bit high. As far as I can tell the Brine pump is running at maximum. Maybe the ground loops are too good??  As I said still on a bit of a learning curve, but very happy so far.


Forgot to say earlier total install took 8 days from start to finish including the weekend. Ground loops were installed by a sub contractor and took 2 1/2 days in total. All the rest was done by 2 guys in 6 working days. (actually it was only 10 man days as one was off for 2 days).

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.
JonG
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« Reply #34 on: December 13, 2015, 10:50:35 PM »

You would usually have a stat to control system side circulation if the buffer is in parallel and a load compensating control back to the heatppump to refine the curve.

Delta on the brine is ideally 3 but 1200 m is a lot of pipe for a 10kw we would have around 600m up here but obviously ground conditions dictate. What is each loop length?

Also not sure which unit u have but the opti pro has some fuzzy logic that settles the delta over time provided pump is man enough.
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« Reply #35 on: December 13, 2015, 11:13:34 PM »

We had lots of discusion on the loops. We are on a shingle bank with pockets of clay.  The installer recomended oversizing the loops as he was worried about running the loops through lots of shingle. There are 4 loops, each 300m. Separation is better than 1m. 150m of each loop is in wet clay, the rest in dirty shingle.  If the ground array is an issue then I guess I could close 1 or even 2 loops off i  the manifold chamber.

Is too much ground loop an issue?

What's the consequence of a temp difference greater than 3 degrees on brine side?

I suspect the controller does learn and has a bit of fuzzy logic, time will tell. It's a diplomat duo g2.

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.
JonG
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« Reply #36 on: December 14, 2015, 10:16:26 PM »

Hi Roger, too much loop can be an issue (see my comments on the other thread about slinkys in Scotland), but provided the coil rating of the cylinder is high enough should be OK.

We experimented with 300m loops on the Danfoss Opti Pro, which I believe is identical to yours in terms of pump head/flow rate etc. and on the 2 units that we used 300m loops we have had similar delta's, and therefore reverted to 200m runs.

The risk is that if the delta gets too wide you can end up with low pressure errors, (refrigerant cooled too much), it hasn't happened on the 2 we have done but I do keep an eye on it at service or routine visits to the property (it is 2x10kw units cascaded), type of glycol used will impact (ethylene based better) just keep an eye on it as the temps drop and the brine gets more sluggish due to the glycol.

The duo g2 does have a modulating pump with some learning ability so it will take time to settle.
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marshman
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« Reply #37 on: December 14, 2015, 10:55:18 PM »

Hi Roger, too much loop can be an issue (see my comments on the other thread about slinkys in Scotland), but provided the coil rating of the cylinder is high enough should be OK.

We experimented with 300m loops on the Danfoss Opti Pro, which I believe is identical to yours in terms of pump head/flow rate etc. and on the 2 units that we used 300m loops we have had similar delta's, and therefore reverted to 200m runs.

The risk is that if the delta gets too wide you can end up with low pressure errors, (refrigerant cooled too much), it hasn't happened on the 2 we have done but I do keep an eye on it at service or routine visits to the property (it is 2x10kw units cascaded), type of glycol used will impact (ethylene based better) just keep an eye on it as the temps drop and the brine gets more sluggish due to the glycol.

The duo g2 does have a modulating pump with some learning ability so it will take time to settle.


Thanks for the info Jon. I assume the problem is low flow rate, thus the wide delta. I would have thought that 4 parallel loops would be OK though. They added Fernox HP-15C (monopropylene glycol) at around 33% concentration to the ground loops, (about 350 litres iirc). Wouldn't have been happy using an ethylene based glycol as the pipes are mainly in the water table , we are in an SSSI and next to a bird reserve so I would be worried about any leaks. Apparently propylene glycol is less poisonous, if a little more viscous.  I did have a play with the speed of the brine pump but I didn't see any difference in the deltas.

You are correct about it taking time to settle. Every time I change the heat curve by 1 degree it takes all day to "adjust" the start and stop temperatures and settle down. Its easy to see at the moment as the outside temperature has been fairly constant.

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 #38 on: December 15, 2015, 01:29:51 PM »

The temperature drop of about seven degrees  implies that the flow is only something like 1000 litres per  hour  or about the same as an ordinary circulation pump with 22mm pipes.   The input temperature  of 13C does seem very high, pipe surface readings can be influenced  by a degree or two  by the surrounding air temperature.    High input temperatures  greatly increase efficiency and also improves output.     I have a  buffer tank on  the input side of the heat pump as  well as on the output side.   It means having an extra pump but it does allow the option to run  two heat pumps  or mix input  sources.   The buffer tank allows a  high circulation rate and the temperature differential stays  under two degrees.  One option for me  is a small wind generator connected to an immersion  in the  input buffer tank.   
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Gavferg
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« Reply #39 on: December 15, 2015, 02:00:57 PM »

I tried much the same pantomine for over a year as apart of the planing process for a complete stone walled cottage refubishment and new build extension for a smaller building up here in scotland and after many many quotes and sales visits the lowest i got was 21.000 , not including the bore holes that seem to be the lastest and only option being offered locally which is likegivingthecompany open access to your bank account until they hit the depth required.It Seems groundloops are dropping rapidly in effiecency arond here after a few years. So we gave up and specified a cheap oil boiler into underfloor heating and spending more insulation and waiting for something better to come along. even the calcs for rhi werent very good running costs were very high. snow
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titan
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« Reply #40 on: December 15, 2015, 04:11:24 PM »

I am glad I didn't read this thread before I installed my system, bloody hell it makes a simple system complicated. I have to say I don't think  a GSHP with a UFH needs weather compensation. A modulating gas boiler maybe or GSHP with rads even. The costs associated with GSHP installations just seem to be rising which is a big disincentive for potential users. Why are buffer tanks used with UFH they are not needed, just more expense, pipework, standing losses. A GSHP with UFH should be as simple as it gets for heating, direct flow from the GSHP at 35 deg C ( + or - a few deg) to the manifold no blender needed and controlled by zone stats what could be simpler.

The flow from my ground array is 9.5 Deg C which is the sort of temperature to be expected at this time in the heating season.
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marshman
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« Reply #41 on: December 15, 2015, 10:15:02 PM »

The temperature drop of about seven degrees  implies that the flow is only something like 1000 litres per  hour  or about the same as an ordinary circulation pump with 22mm pipes.   The input temperature  of 13C does seem very high, pipe surface readings can be influenced  by a degree or two  by the surrounding air temperature.    High input temperatures  greatly increase efficiency and also improves output.     I have a  buffer tank on  the input side of the heat pump as  well as on the output side.   It means having an extra pump but it does allow the option to run  two heat pumps  or mix input  sources.   The buffer tank allows a  high circulation rate and the temperature differential stays  under two degrees.  One option for me  is a small wind generator connected to an immersion  in the  input buffer tank.   

I assume the sensors are properly connected to the pipes and not influenced by the outside air - but you never know. My buffer tank also has an immersion fitted, but its not connected to anything yet. I suspect if I did put some heat into it the controller would get confused and its calculations would get even more fuzzy Grin

I checked the flow rate of the ground loops today at the manifold chamber. Each loop is fitted with a crude flow meter. All loops were reading the same level of flow, as you would expect, and all were showing just above 8 litres per minute. So four loops at 8 litres per minute gives a total of 32 ltrs / min = 32 * 60 = 1920 ltrs per hour minimum.

The heat pump can control, modulate as Jon says, the speed of the brine pump. I have set it to max but this is just the start up speed, not sure if it falls back to what the controller is happy with. I'm tempted to dive in with a calibrated thermometer and measure the flow and return temps direct to see if the displayed temperatures are correct, or even monitor the volts on the pump to see if it is running flat out.

I wouldn't be bothered except everyone seems to be saying the differential is quite large and if it is "stressing" any part of the heat pump I would like to get it sorted to ensure it has a long life!

Roger
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« Reply #42 on: December 15, 2015, 10:48:05 PM »

I am glad I didn't read this thread before I installed my system, bloody hell it makes a simple system complicated. I have to say I don't think  a GSHP with a UFH needs weather compensation. A modulating gas boiler maybe or GSHP with rads even. The costs associated with GSHP installations just seem to be rising which is a big disincentive for potential users. Why are buffer tanks used with UFH they are not needed, just more expense, pipework, standing losses. A GSHP with UFH should be as simple as it gets for heating, direct flow from the GSHP at 35 deg C ( + or - a few deg) to the manifold no blender needed and controlled by zone stats what could be simpler.

The flow from my ground array is 9.5 Deg C which is the sort of temperature to be expected at this time in the heating season.
Hi titan,

The weather compensation is really just the cost of the outside sensor and some software in the controller, doesn't really add to the cost of the system. I agree regarding the buffer tank, it is a waste of space & money, but AFAIK the MCS regs call for it to ensure that the heat pump doesn't cycle too often - more for radiators than UFH - the result of a one size fits all policy! My system is simple really, one Grundfos circulation pump moving water round all the UFH loops via two manifolds, one upstairs, one down, and back through the buffer tank. No stats, no valves, no nothing other than the expansion vessel.

The original UFH installed in the mid 1980's had a permanently pumped system with two thermostic valves and a bypass. One thermostatic valve acted to limit the maximum water temperature flowing through the floor to around 45 deg C. The other was the room stat. As the room warmed up it gradually reduced the temperature of the water flowing through the UFH until such time as an equilibrium was reached. This in my opinion, and the opinion of Wirsbo at the time, was the best way to set up and control their UFH. The modern  "conventional" way seems to be the same as with radiators, keep the water temp constant then start and stop the circulation pump. The problem with that is UFH, especially the one in this house has a very slow response time, so the system is very sluggish and is almost never the right temperature.  My "new" heatpump system does the same thing as the my original system. It controls the temperature of the circulating water to achieve a constant temperature in the house. The only difference is that it does it by monitoring the outside temperature, deriving the heat loss from the house and hence its heat requirement. So I end up with it running 24/7, a nice even temperature everywhere and a heat pump that at the moment is cycling once every 90 minutes or so.

The other thing is my heat pump compressor is not inverter driven so as far as I know it is on or off so it couldn't maintain a constant temperature unless it had a massive buffer tank and some form of temperature mixing valve.

Having said all that every house is different, every install is different, heating system and UFH systems are different and have different characteristics, finally, the house occupants needs/objectives are different. So what works well in one situation is no good for another. I've lived with a Wirsbo UFH system for over 25 years and love it. Its basically a 20mm (might be 22mm) PEX pipe sitting in an aluminium spreader plate that is sandwiched under the floor boards against insulation. The contact area between the pipe, the aluminium plate  and the underside of the floorboard is very good. Pipe spacing is about 12" (300mm). I have 4 loops covering about 100 sq m down stairs and a similar amount upstairs.

Time will tell what the long term temperature of the ground loops will be but I appear to be lucky that they are sitting in the ground water for the most part.

Just the mystery of the large delta to solve Huh


Roger
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« Reply #43 on: December 16, 2015, 09:24:40 AM »

... It Seems groundloops are dropping rapidly in effiecency arond here after a few years. ...

Interesting. Any idea why that might be?
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titan
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« Reply #44 on: December 16, 2015, 11:50:19 AM »


I'm tempted to dive in with a calibrated thermometer and measure the flow and return temps direct to see if the displayed temperatures are correct, or even monitor the volts on the pump to see if it is running flat out.


I use one of these    http://www.ebay.co.uk/bhp/infrared-thermometer
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