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Discuss Intergrating stove ,solar thermal and ground source heat pump. in the Renewable Energy area at PlumbersForums.net

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voivod

Plumber
Gas Engineer
Have been asked to quote to fit the above in a house . Have done them all individually or linking two out of three but usually with gas or electric back up.
the only time have see all three linked (not by me ) the customer was complaining about lack of hot water from their thermal store especially when heating running and no stove fired up.

Its a 16kw ground source heat pump .Just looking for ideas and drawings of best practise as customer supplying :cuss:, and seems to be from different manufacturers. Want to get ahead of the problems before they turn up lol

Thanks in advance
Steve
 

snowhead

Esteemed
Plumber
What's the total Kw rating of all 3 and who specified the 16kw ground source?
What size Thermal store?

It's going to struggle I suspect.
 
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V

voivod

Plumber
Gas Engineer
Its a new kit built . Specs by sap calcs and architect.
They hadnt thought about how to do it all so have asked me to work something out with their choice stove /heat pump and solar thermal .
I can stipulate specs of buffer etc
 

Nostrum

Plumber
Gas Engineer
Question to ask is why?

Just because you can doesn't mean it's the best solution.

If the heat pumps sized right it should be sufficient. Solar through a twin coil cylinder would be advantageous. Keep the wood burner for room heating only rather than wet side.
 
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voivod

Plumber
Gas Engineer
its the customers idea...trying to figure out best way.
And also to figure best bugger tank size for it :(
Fecking hate when customer wants to get own stuff. usually get 1 manufacturer and get them to help spec .
 
I think I would be talking them out of it or walking away especially without the supply margin. ST only saves a truly marginal amount PA based on several studies incl. EST.

High temps in the store from the stove and ST could trip the HP stat or cause high return errors.

Stove is gravity (usually) and the rest sealed, which side has the HEX therefore and how do you design the control strategy?

It will also make the RHI complex too.
 

Nostrum

Plumber
Gas Engineer
Buffer tank or store?

Buffer volume will depend on total system volume and minimum cycle time etc specified by heat pump manufacturer. You may need 200 litre's, you may need none at all.

Don't go for a thermal store for the reasons above. A twin coil cylinder would work best if you want to include solar thermal.

The costs involved in a wet system wood burner installation outweigh they gains to be had unless it's is entirely your only source of heat. Get them to rethink and stick with a dry stove.
 

Worcester

Plumber
And then you've got to control the heating / emitter side correctly depending upon the temperature in the store and heat load. It can be done, though needs to be designed FIRST. There's a charge for that :)

SAP not adequate for the full heating design in this instance either - if you install heat pumps under MCS you know this though..

New build? - any MVHR?

Check the Akva site for possible schematics, though you won't get design details from there.
 
OP
V

voivod

Plumber
Gas Engineer
Thanks all. Been to visit them today . They have decided to have heating by ground source (no buffer). And seperate hwc fitted heated by ground source and solar thermal.With an electric back up . This is the manufacturers spec so should be ok
Told them stove would be not good as they have turned house upside down (bedrooms down / living upstairs , cylinder downstairs.
And full MVHR so can spread heat from stove .
They also didnt seem to realise how big a buffer tank would be needed .
Common sense seems to be taking hold ...for now lol
 

Worcester

Plumber
Even good practice would put a 10 litre/kW buffer in for the GSHP .. makes a big difference to the efficiency, cycling etc - I don't know of a single GSHP that recommend no buffer - what make is it that they are looking at?

GSHP's aren't generally inverter driven like ASHP's so they don't modulate, they are either on or off, hence the buffer...

!6kW, single or twin / cascade, if twin compressor or cascade, you only need to buffer size for the larger of the two - think about it... so if twin 8KW, only need an 80 litre buffer.
 
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N

Norcs

The wet stove is good option. About 8kw to water is ample and only use it to heat the bedroom floor + heat leak rad.
If ufh is being fitted then fit rads for the stove.
On its own separate system then the controls are simplified.

Usual set up with hi-lo stats, injector T, 28mm primaries, gravity rad on the first floor and pumped to the ground floor.
Then the customer has back up when the heat pump fails and cheap to implement.
 
Plenty of manufacturers are happy without, Danfoss, IVT, IDM, Heliotherm (which also modulates), Kensa all have schematics without buffers.

Generally they are better going straight to screed than rads but provided the flow volume, flow rate and min system volume is available it can make for a very simple system. We have done plenty where with good design the UFH can be totally open circuit.

Small buffers can often cause more cycling due to mixing, especially with units that sample the system to effect a response and in any event TP controls can quickly upset the stratification pumping in and out even if the HP circulator is off. Some of the Austrians recommend 30 litres per kw for this reason.

Combined buffer and hot water buffers are also common in Austrian installs, which save some space but are generally 500l plus to give a similar tapping volumes to a 300l cyl.
 
N

Norcs

The buffer connected in parallel means no mixing can occur. Longer run times in theory should be possible than in series where mixing will inevitably occur.
 
We thought that, but testing by Kiwa(?) proved otherwise, their research indicated that the best layout for run times was actually in series on the return.
 
N

Norcs

None of those schematics represent the viessman and kensa "series" connection design.
Because they fit the buffer on the by pass loop and fit stats at the top and bottom of the buffer. (kensa fit a 0.4 bar by-pass valve)
So their buffer is heated from the top down and cooled from the bottom up. Ideal for twin stats operation and eradicating cycling.
Its a shame kiwa didn't run that test.
The engineers at viessman are no slouches. Kensa copied their design as viessman were using it decades ago.

And of course as the buffer is being depleted in the CH any demand from the HW can still be fulfilled by the heat pump.
 
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N

Norcs

kiwa state
"If the required system volume is not available the system should be supplemented by a two pipe buffer tank placed in the return pipe to the heat pump."

The problem with that statement with its corresponding schematic in fig 26 is that the space heating may be satisfied and the buffer is not recharged fully. So when the system starts again the heat pump just cycles on instead of using stored energy alone as per the viessman design.
 

Nostrum

Plumber
Gas Engineer
The buffer should always be fully charged at the end of a cycle as the heat pumps set point is based on the buffer / return temperature and not switched by the room stat or similar. Likewise when an emitter circuit draws off some heat, the heat pump is triggered by a drop in buffer/ return temp.

The buffer on the return in series is purely to increase the total open circuit system volume, with the exception of defrost cycle on air source.
 

Worcester

Plumber
We thought that, but testing by Kiwa(?) proved otherwise, their research indicated that the best layout for run times was actually in series on the return.
Not quite...

What they said was:

If the required system volume is not available the system should be supplemented by a two pipe buffer tank placed in the return pipe to the heat pump.
That's a volumiser not a buffer. See their schematics.

Also fully read my thread on two and four port buffers. There is a shed load more experience out there since that report was published in 2013.

I still stand by my quote that
I don't know of a single GSHP that recommend no buffer
Yes they do have schematics without buffers and permanently open loops in ufh is one way of dealing with it, if you ask them, they will always say that a buffer is best.

As KIWA point out there is quite a big difference between ASHP and GSHP, most ASHP's are inverter driven so modulate down to 30% or less, most GSHP's are fixed output, on or off, so no modulation,

Out of interest, which GSHP's are inverter driven / can modulate their output (not twins / cascades that switch on or the other on or off) ?
 

Worcester

Plumber
Sorry guys, duplicated some of your comments, didn't realise it had popped on to page 2 of the thread !! :)
 

Worcester

Plumber
Also shame that for the DHW consumption they didn't use the official standard - they exist specifically for this reason.

Tapping Cycle No.2 from EN 13203-2. Tapping cycles are set daily profiles of hot water draws, including the start times and energy per draw, developed by industry to enable different appliances to be tested with exactly the same hot water load.


Tapping Cycle No.2 means 5.845 kWh of energy is contained within the water drawn per day.

The actual volume of water drawn depends on the inlet and outlet temperatures – if the water is heated from 10 to 50°C, this equates to 124 litres per day. This unit under test is set to 55°C as per the manufacturer instructions; actual tank temperature varies between 49.4 and 57°C as it cycles on and off on the controls. The cold water feed average for February is 10.7°C.

Results for February (1st – 20th) show the daily hot water volume to be an average of 114.6 litres, with a minimum of 111 and maximum of 118. For comparison, a 2008 study by EST [1] found the mean household consumption to be 122 litres/day, using data from about 120 houses. The Government’s Standard Assessment Procedure, SAP 2009 [2] uses 36+(25*N) litres per day, so for 3 people this is 111 litres and for 4 people 136 litres. The tapping cycle is therefore very representative.

If a lower set point were used, e.g. 50°C, then more hot water volume would be drawn to make up the 5.845kWh daily demand.

For more details, please look to BS EN 13203-2:2006


That's the problem with govt appointed consultants - making up their own tests !
 
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Nostrum

Plumber
Gas Engineer
Thermia diplomat inverter, 3 phase only for the minute but single phase is coming.

You'll see them enter the market in the next 12-18 months from most manufacturers. I've been to Sweden to see thier factory and spoken to some of the head honchos about inverter technology.

It seems that the only reason they're investing into it is because the likes of Mitsibishi, Samsung etc have forced the market down this route with their air con technology.

Buffer volumes up to about 200 litres tend not to allow for very efficient stratification, so mixing will occur on a 4 port set up. We've still been advised to use them in this way where hydraulic separation is required, but return in series is favoured.

Another configuration is a 3 port whereby the flow passes through the buffer in series, but with the addition of a return from buffer if flow rates through emitter circuits drop off.
 
Heliotherm and Mastertherm (i think) make fully modulating ground source units. The Heliotherm is very expensive and in tests performs no better in terms of SCOP than high end GSHP's like IDM etc.

They and IDM are more than happy for you to go direct to screed provided volume and flow rate are available. The reason we started doing 4 pipe buffers at 30l per kw was due to the mixing that occurred in the smaller buffers.

Over the long haul the impact is probably negligible and so many other factors to take into consideration like location of buffer, type of property, interlock, cyclical rate of downstream controls etc. There is no perfect solution.
 
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