GSHP likely to be better choice...

[Digmixfill]

I'm going to have underfloor heating and am still undecided on ASHP or GSHP to feed. Periodically i hunt around for new learning and make some notes here and there.

Hunting around this morning i came across this pdf from Kensa.  GSHP vs ASHP V4

 

 "Conclusion
ASHPs appear to be a straightforward and easy technology for salesmen to “box shift”.
There is a lack of expertise of those selling and installing ASHPs – and this extends to those that are buying
them because the technology has been “over-sold”.
In practice, GSHPs are likely to be the better choice, for the longer time, in most applications."

 

ASHP must be competing favourably.

[ProDave]

What else do you expect a manufacturer of GSHP's to say?  They are hardly likely to endorse ASHP's are they?

 

I went through the same decisions, initially I was sold on the idea of a GSHP.  That was until I found out the cost of all the pipe you have to bury.  Even though at the time I had my own digger so installation would have been "cheap" it was still a lot of work.  Then there is a considerable amount if antifreeze to fill the ground collector pipes with which is supposed to be replaced every 10 years with replacement and disposal costs.

 

And all that extra expense for what?  A small improvement in the COP compared to an ASHP.

 

Another deciding factor for me was noise.  Generally a monoblock ASHP sits outside so the compressor and fan, the but that makes noise, is outside and completely inaudible from inside the house.  But a GSHP (and a split ASHP) has the compressor inside the house, so you have to think very carefully where you are going to put it and if necessary how you will soundproof it.

 

I have only wired one GSHP  and the owner decided under a unit in the kitchen was a good place. It was like having an extra noisy fridge running all the time.

 

Also I take issue with their statement that an ASHP must be used with a buffer tank. I can assure you mine has been working fine all winter without one.

[Jeremy Harris]

I looked at this in detail, and the small Kensa unit was initially my preferred unit.  However, the cost was astronomical compared with an ASHP, and would never have been recovered from the small saving through the life of the unit.

 

The GSHP install, with me doing most of the work, was going to be around £8k, and would run with a true COP (allowing for pump losses, which often aren't mentioned) that would have been about 8% better overall than an ASHP.  Our ASHP cost around £2k (installed).

 

Our ASHP costs maybe £200 a year in electricity (I've not checked lately but suspect this is a big over-estimate), so if we had a GSHP we'd save maybe £16 a year.  To recover the ~£6k premium for installing a GSHP, and ignoring the higher maintenance costs for a GSHP then it would take around 375 years to recover the additional cost just from the small energy saving.

 

We've been consistently getting a COP of over 3.5 from our ASHP, often it runs at around a COP of 4, so there isn't much difference between it and a GSHP in practice.

[joe90]

I agree that there are some issues with badly installed ASHP,s but I installed my own with basic plumbing skills and lots of helpful knowledge from this forum, it’s not rocket science but needs doing properly. I have plenty of ground for an GSHP but it didn’t stack up for us at all.

[scottishjohn]

as said above cost of GSHP is far too high

in Uk we do not get the very low temps like canada where an ASHP would not work  due to being -20 for long periods 

only time i would consider a GSHP is if i had a lake i could throw a big loop in --then the costs for installation  change dramatically  and make it the right choice 

[Digmixfill]

Now that our floor has 200mm of insulation i'll need to rework the calculations, but originally it was proposed that we needed a 10kW GSHP.

Installation costs won't be a factor because i'll self install for either.

 

I'm right in the middle of the fence regards one over the other. SWMBO is on the side of the GSHP at the moment. She thinks the ASHPs look a bit flimsy and wouldn't fare well against a badger etc.

 

 

[Jeremy Harris]

Even DIY the installation costs for a GSHP will be a great deal higher, just because GSHPs tend to be more expensive, they a ground loop and also require pretty expensive antifreeze.  I doubt that any GSHP will ever recover the higher initial cost through life (and, FWIW, I was going to self-install a GSHP, and my costings above were based on that).

[TerryE]

19 hours ago, Digmixfill said:

the ASHPs look a bit flimsy and wouldn't fare well against a badger etc

 

I really don't think that this is an evidence-based view, and is hardly a good reason for adding £10K or so to your costs as well as digging up a large chunk of your site.

[Triassic]

19 hours ago, Digmixfill said:

I'm right in the middle of the fence regards one over the other. SWMBO is on the side of the GSHP at the moment. She thinks the ASHPs look a bit flimsy and wouldn't fare well against a badger etc. 

 

Ask her what she'd like to spend the £10k difference on, maybe a nice holiday, nicer fixtures and fittings! I know what mine would say!

[scottishjohn]

gshp will give same cop all year round --even in really cold weather,ASHP could be done to near 1-1 in very cold weather  --that's the difference

and some will also support that they  give better COP than ashp  all the time 

but without a lake to dump your coil in --never going to be better than ASHP in uk climate.

10 k difference between air +ground -- will be more than that   in some cases -if ithas to be bore hole and not trenches 

I was quoted 13k just to drill the bore hole +no warranty that i wouldn,t need another one -but if done when drill rig was still there it would save 3k

all depends on the ground you have 

 

Edited March 23, 2019 by scottishjohn

[Jeremy Harris]

ASHP COP is more affected by humidity than temperature in practice; changes in outside air temperature alone don't make a massive difference to performance, which is why places like Finland have so many ASHP installations (cold, dry air is pretty good, as it doesn't give much evaporator icing).  The biggest single cause of a poor COP is asking any heat pump to operate with a higher temperature differential than it was designed for.  This differential is more critical for an ASHP, as most single-stage heat pumps (whether ground, water or air source) won't operate efficiently with more than about a 60°C temperature differential. 

 

The impact of this is greater with an ASHP than a ground or water source heat pump just because a ground or water source heat pump will have a fairly steady input fluid temperature.  Whether this is actually important or not depends on the desired output temperature.  For example, I run our ASHP at 40°C flow temperature, which is more than enough for the heating and hot water pre-heat (we could drop this by another 5°C with no significant impact).  This means that our ASHP carries on working fine down to about -20°C outside, when it starts to limit because of the working limitations of the refrigerant gas used (there's still plenty of heat available in air at -20°C). 

[Stones]

When I looked at GSHP vs ASHP, I found that with a heating demand below 5000 kWh/yr it would actually cost MORE to run a GSHP vs an ASHP once you had taken into account the energy cost for the additional pumps required in a GSHP system, and that was before factoring in the cost of replacement antifreeze, or the higher capital costs. I recall pointing this out to the salesmen and they all, to a man, responded by saying 'but look at the RHI payments you would get'.  Enough said.

[TerryE]

23 hours ago, scottishjohn said:

ASHP could be done to near 1-1 in very cold weather

 

This is misleading as a general observation.  Yes, the heating system has to cope with worst case conditions, but the expected running costs are based on appropriately seasonal weighted averages.  For example if you are running one of the Mitsubishi Ecodan's with an outlet temp of 35°C (the sort of temp to feed into UFH) then the CoP is just over 4 at an external temp of 7°C falling to around 2.8 at -3°C.  How many days a year do we have average temperatures below -3°C?

[scottishjohn]

1 minute ago, TerryE said:

 

This is misleading as a general observation.  Yes, the heating system has to cope with worst case conditions, but the expected running costs are based on appropriately seasonal weighted averages.  For example if you are running one of the Mitsubishi Ecodan's with an outlet temp of 35°C (the sort of temp to feed into UFH) then the CoP is just over 4 at an external temp of 7°C falling to around 2.8 at -3°C.  How many days a year do we have average temperatures below -3°C?

no  it is not as it was used in comparsion to a gshp where the cop does not suffer in very cold temps 

i have already said ashp is best choice for uk 

UNLESS you have a lake where yo can simply throw a big coil of pipe in --eg no costs for laying pipes and remaking ground  or drilling bore holes

then and only them is a GSHP  worth considering 

[Digmixfill]

On 23/03/2019 at 13:52, TerryE said:

 

I really don't think that this is an evidence-based view, and is hardly a good reason for adding £10K or so to your costs as well as digging up a large chunk of your site.

My better half needs no real reason to add £K to anything.   Her point is reasonable though. When a badger wants into something they can make quite a mess of things.

 

The ground here is pretty moist marl. If i were to install a ground loop it would be straight pipe about 5ft deep.

 

I've got a few years worth of recoded temperature and humidity, it might be useful for some ASHP number crunching.

 

Are the above ASHP COP figures of 4@7°C and 2.8@-3°C sensible to work with and achievable with an average install? (By average i mean one that isn't specifically tuned to achieve maximum figures)

[Ferdinand]

57 minutes ago, Digmixfill said:

badger

 

What is the cost of a badger proof cage for an ASHP? Less than the difference?

 

F

[Onoff]

13 hours ago, scottishjohn said:

no  it is not as it was used in comparsion to a gshp where the cop does not suffer in very cold temps 

i have already said ashp is best choice for uk 

UNLESS you have a lake where yo can simply throw a big coil of pipe in --eg no costs for laying pipes and remaking ground  or drilling bore holes

then and only them is a GSHP  worth considering 

 

Hypothetically what sort of area & depth would a lake need to be, to get reasonable performance numbers from a GSHP?

 

Half thinking of people with sloping sites. Would it be worth berming the lower end and creating a big "pond"?

 

I know some on here have lakes already and are planning a GSHP, others have dug ponds. Presumably the pipes have to be insulated from the point of entry into said body of water and some distance in to it too?

 

Fascinating.

[Triassic]

1 hour ago, Ferdinand said:

 

What is the cost of a badger proof cage for an ASHP? Less than the difference?

 

F

What sort of Badgers do you have! At worse ours eat the odd plant and head butt to odd car late at night!

[Onoff]

3 minutes ago, Triassic said:

What sort of Badgers do you have! At worse ours eat the odd plant and head butt to odd car late at night!

 

Ours plough the lawn looking for yellow jacket grubs! Make a right mess:

 

 

[Ferdinand]

6 minutes ago, Onoff said:

 

Ours plough the lawn looking for yellow jacket grubs! Make a right mess:

 

 

 

Bet that lot came from Thanet.

 

Quite some badgers who can nearly tip over a mini-tractor.

Edited March 25, 2019 by Ferdinand

[Onoff]

19 minutes ago, Ferdinand said:

 

Quite some badgers who can nearly tip over a mini-tractor

 

He was jet washing it...

[ProDave]

16 minutes ago, Onoff said:

 

He was jet washing it...

That is one clever badger.

[Jeremy Harris]

3 hours ago, Digmixfill said:

I've got a few years worth of recoded temperature and humidity, it might be useful for some ASHP number crunching.

 

Are the above ASHP COP figures of 4@7°C and 2.8@-3°C sensible to work with and achievable with an average install? (By average i mean one that isn't specifically tuned to achieve maximum figures)

 

In practice I've found that the COP of our ASHP is always well over 3, often over 4 for a lot of the time.  The lowest outside air temperature we've seen has been about -8°C, but that's irrelevant. as all you need to work out the overall running cost/energy use is the mean outside temperature (and, perhaps, humidity).  From that, and from knowing the flow rate, operating time and temperature you can work out the mean COP, which is all that matters.

 

The worst case we've found is when the air temperature is a few degrees above zero, but the air is very humid.  That can create a situation where the ASHP needs to defrost, but only if it's heavily loaded.  By making sure that ours never needs to deliver water at more than 40°C I've been able to stop it defrosting under any condition we get here, which makes a significant difference to its efficiency.  I can sit down later this week and work out the mean COP, but at a guess I'd say it's well over 3.5.  In worked out that the mean COP of a GSHP could be around 8% more efficient at best.

[Digmixfill]

8 hours ago, Triassic said:

What sort of Badgers do you have! At worse ours eat the odd plant and head butt to odd car late at night!

 

They've not had at a car here yet, but they once made quite a mess of a corner of a tin shed that they seemed interested in.

 

@JSHarris I've got temperate and humidity records.  Just had a quick scan through the database and the min and avg recorded temperatures between August and March for the past 5 years are:

 

2014-2015 min -2.9 avg 14.36
2015-2017 min -3.0 avg 13.23
2016-2017 min -3.8 avg 9.46
2017-2018 min -7.4 avg 11.74
2018-2019 min -5.3 avg 15.16

 

 

[Big Jimbo]

On 25/03/2019 at 07:46, Onoff said:

 

Ours plough the lawn looking for yellow jacket grubs! Make a right mess:

 

 

After they have finished with your lawn, do they do the maintainance on your mower ? Very impressive if they do. My mower is out of action at the moment. Could you have a word with your Badger gang please ?