Crazy ASHP idea?

[Jeremy Harris]

44 minutes ago, mike2016 said:

Just curious - what is the cost multiplier of GSHP over ASHP? Is it more than 2x?

It depends a fair bit on the ground work needed, but double the price of an ASHP seems about right unless you're lucky enough to have a big lake or perhaps a stream flowing through your garden, where you can just drop in a collector mat.

[ProDave]

I looked at a GSHP. The cost of the pipes AND the antifreeze to fill them is as much again as the heat pump. I could have done the ground work myself with my own digger but it still would have been a lot of work. then there is the anti freeze needs replacign every 10 years, another expense and a problem to dispiose of the old antifreeze.  I just decided it wasn't worth it.

Niow a heat pump fed from the water in a burn, Too much regulatory hurdles, but one might "experiment" later on when it's all signed off and nobody is looking........

[SteamyTea]

On 14 June 2016 at 13:31, mike2016 said:

Maybe with all this global warming we'll not get below 6 degree much anymore anyhow?!!

Would be nice, but as air temperatures get higher, so does the variation and negative skew of the distribution, so you will still get extreme cold occasionally.

You will also get extreme rainfall, which in itself is not a problem, but when mixed with rapidly changing air temperature, higher solar radiation levels, plus faster windspeed, humidity levels can be higher.  It is the relative humidity that is the real problem with ASHP.

Basically what you end up with is two variables that are both non-linear to each other.  This is not usually a problem as you can disregard half the solutions e.g. you may end up with an extreme answer that is impossible e.g. -100K or RH +200.

The trouble starts where you get to a point where the external air temperature and RH are in the range where the ASHP is at its least efficient.  You may have noticed that there are 'gaps' in the manufacturers' performance data.  This may well be where the performance is not to good e.g. 3°C.  This is why there is not a simple equation that gives a correct answer.  Performance data is generally created from observation.

Thankfully ASHP now modulate to take this into account, so this is where you can get an advantage.  If you get the largest ASHP that you can practically install, but one that will modulate down to your minimum requirements (we usually look at maximum requirements only), you will reduce the chance of frosting, or at least extend the time it takes to frost up.  A secondary advantage is that they will be working at the lowest fan speeds, this keeps the noise down (not that they are noisy these days).

The main thing to remember is that they are not gas or oil burners, they work within different temperatures ranges.

If money is not so much of a problem, then consider a GSHP, but one with boreholes rather than a horizontal pipe array.  These are much more consistent.  Depending on your location and geology, get a water supply fitted at the same time, that may save you a few hundred quid a year.

[mike2016]

Thanks!

Interesting the suggestion to "Go Large" on ASHP's! I'll have to look closely at the manufacturer specifications. I've just installed an energy meter in my current house and plan to extend this in my new build to get more granular readings, especially the ASHP. I was talking to one company yesterday about several Heating/hot water options, now just need the BER file to send over to them to see what they suggest.  

 

[Jeremy Harris]

31 minutes ago, mike2016 said:

Thanks!

Interesting the suggestion to "Go Large" on ASHP's! I'll have to look closely at the manufacturer specifications. I've just installed an energy meter in my current house and plan to extend this in my new build to get more granular readings, especially the ASHP. I was talking to one company yesterday about several Heating/hot water options, now just need the BER file to send over to them to see what they suggest.  

 

By accident (because it was available at the right price, as surplus new stock) I bought a 7 kw inverter controlled heat pump, even though I knew our house would never need more than 2 kW of heating at the very most.  It has proved to be an excellent match to our needs, as when at low power levels it seems to be extremely efficient, primarily because it rarely, if ever, defrosts.  The other benefit is that when running at these very low outputs it is extremely quiet.  ST here has stood next to it when I turned it on to illustrate the noise, and can attest to the fact that it's hardly audible above the background noise.  The MVHR air intake, high up on the wall behind the ASHP, is noisier, although even that isn't as noisy as a normal extractor fan.

[dogman]

An interesting result of a ground source heat pump is the change in ground and air temperature, I will no doubt get told not possible but a house near mine had an extremely large pipe field built . The field is used by local people to ride horses and the ground and air over the field is noticeably colder when the pump is running. My daughter had noticed it herself 

[mike2016]

I'd heard about the impact in ground temperature in that it takes 4 years to stabilize but hadn't heard about air temperature being affected! With a large pipe field I guess this is the impact it can have. I'd be tempted to drill an angular borehole under my favourite neighbours house and drop their temperature a bit! Be useful around Halloween too....

[reddal]

23 minutes ago, mike2016 said:

I'd heard about the impact in ground temperature in that it takes 4 years to stabilize

I've always been a bit dubious of this - the idea that ground temperature impacts can persist between seasons. I understand a GSHP can change the ground temp in the short term - but the idea that the change in temperature will hang around for months or even years doesn't make sense to me.

We build houses with all kinds of fancy insulation - and even with all that - with no heatsource any temp difference between the inside and outside of the house will equalise within a few days. And yet a temp difference in the ground made of soil and wet mud with no insulation at all will remain for months/years?

Surely any temperature impact a GSHP has on the ground will equalise in a few days at most?

- reddal

p.s. apoligies for the derail...

[SteamyTea]

Also worth remembering that the majority of the energy that a horizontal array receives is from rain water, that is then heated slightly by solar radiation.

It would be possible to make a rough calculation as to how much it may cool the ground.  The air temp is a red herring I suspect.  Air temperature is generally by mass movement and not really affected much at the very small scale.

There have been cases where the array has not been buried very deep and the ground has frozen.  This causes some heaving as the liquid water turns to ice and expands.  I have only heard of one incidence of this over at the 'other place'.  It was apparently caused by undersized pipework being too shallow.

[Inchbyinch]

On 13/06/2016 at 14:27, joe90 said:

Using an ASHP to get water to 40' and boosting for "hot " water is exactly what I plan to do. I did wonder if it was possible to get the ASHP to recognise when it was just about to run a defrost cycle and get it to stop itself, that way you could get the ASHP to get the max temp out of it without ruining the COP.

Joe/Jeremy,

Is the in line stieble the best option for "boosting" the water? water at 40 + 5 deg @ 10-14l per minute would give a demand of 4.9 kw which means you could run two showers at the same time off a 12kw unit?

An immersion would then boost to 65 once a month or so?

This sound like the correct solution? I'm thinking a 500l UVC for hot water. no Solar

Thanks

Ed

[Jeremy Harris]

6 hours ago, Inchbyinch said:

Joe/Jeremy,

Is the in line stieble the best option for "boosting" the water? water at 40 + 5 deg @ 10-14l per minute would give a demand of 4.9 kw which means you could run two showers at the same time off a 12kw unit?

An immersion would then boost to 65 once a month or so?

This sound like the correct solution? I'm thinking a 500l UVC for hot water. no Solar

Thanks

Ed

There may be other options around, but I've not found them.  I looked around a fair bit and there were one or two that I thought might modulate power the way the Stiebel Eltron one does, but Stiebel were the only company that could confirm that they were OK with a warm water feed and would work as a variable boost heater (their technical chap was very helpful and the reason I bought their unit).

What you describe does sound like a simple and easy solution.  The reason I didn't go for the 12kW version was only down to the capacity of my CU, I couldn't find RCBOs that were rated at higher than 50A for it and you need a 60A one for the 12kW version.  If I was starting from scratch I'd probably fit a separate small CU just for the water heater, to avoid having a 50A load through the main unit.

[Inchbyinch]

Thanks Jeremy,

Yes it sounds almost too simple to work. Is once a month for a "sanitary" clean  good enough and is 500L UVC enough do you think. We have a young family and hot water can be in demand but not always.

 

[PeterW]

500 is ample - you may want twin immersions though. 

Once a month or once a fortnight for leigionella is fine  

[Inchbyinch]

Thanks Pete.

I'd say that's our solution alright. Now to try and get a handy ASHP. eBay here I come.

[PeterW]

There are a few !