Thermal mass and ground loop heat pump question
Gareth Jones
Hi Folks,
Although this is a posting from the UK, you US people seem to have a
load of experience in this area so please don't let a small stretch of
water put you off replying ;-)
One question in two halves:
I want to install a ground loop heat pump to drive a wet underfloor
heating system in the house I'm building. This is constructed from
conventional twin wall concrete blocks with a well insulated cavity. It
has two solid floors, both of which will be approx. 6in thick with the
Pex pipe embedded in the top 2 inches. There is a fairly high degree of
insulation under the slab, in the walls and the roof. We're using good
old USA Anderson windows (as they seem to be better than most of the
British rubbish!) low e, argon filled, so for the UK, its a well
insulated dwelling (without going mad!).
Because it has such a large mass (and all the internal walls are 4in
solid block as well) I am hoping that I can use economy7 electricity to
run the heat pump. (Don't know if you have this outside the UK - its
where you can use off peak power between midnight and 7am at about a
third of the price).
I could spend weeks doing research into all the co-efficients and trying
to work out thermal mass and heat transfer calculations, but frankly,
most of the time, an experienced HVAC engineer will have come across
similar situations and will have a gut feeling about what can and can't
be done.
So I'm wondering, if you heat up the floors in the night, will the
thermal mass of the house be enough to keep a reasonable temperature for
the 17hr off period until the next 7 hour heating cycle?
(We will probably have a small wood burner in the main living area just
as a backup ;-)
Which leads me on to the second half of the question:
I have located a supplier of heat pumps. There are three models in their
range. They provide 4, 7 and 11kW outputs.
The house is a reasonable size - say 5 bed, approx. 4000 sq ft. I've
found a study on a similar property where they put in a 4kW GLHP. They
calculated it would provide around 50% of their needs, but in reality
provided 80%.
So I'm guessing the 7kW would be fine - however our own calculations for
room by room heat loss indicate that we need much more than this (but
this is using standard calculations designed for standard houses!)
So this makes me think the 11kW would be the safe option, but of course
it uses a fair bit more juice (and also, the starting current is 111amps
which worries me slightly!!). I'd rather use the 7kW if I could.
Again, if anybody has experience in this area, I'd be very grateful for
your comments.
--
__________________________________________
<Gareth Jones> usenet@_ns_swansea.demon.co.uk
"Reality sucks - go watch a Star Trek"
To email, remove the '_ns_' from
usenet@_ns_swansea.demon.co.uk
__________________________________________
Nick Pine
>I want to install a ground loop heat pump to drive a wet underfloor
>heating system in the house I'm building. This is constructed from
>conventional twin wall concrete blocks with a well insulated cavity...
>The house is a reasonable size - say 5 bed, approx. 4000 sq ft...
With 2000 ft^2 of US R10 walls (2" Styrofoam) with 200 Btu/h-F of conductance?
>It has two solid floors, both of which will be approx. 6in thick with the
>Pex pipe embedded in the top 2 inches. There is a fairly high degree of
>insulation under the slab, in the walls and the roof.
US R10 again? With about 4000 ft^2/R20 = 200 Btu/h-F of conductance and
4000x6/12x25 = 50K Btu/F of floor heat capacitance and 4000ft^2/R10
= 400 Btu/h-F of roof conductance?
>We're using good old USA Anderson windows (as they seem to be better
>than most of the British rubbish!) low e, argon filled...
Say 400 ft^2 of R4 windows with 100 Btu/h-F of conductance?
>Because it has such a large mass (and all the internal walls are 4in
>solid block as well)
Another 2000x4/12x25 = 16.7K Btu/F of heat capacitance...
>...if you heat up the floors in the night, will the thermal mass of
>the house be enough to keep a reasonable temperature for the 17hr
>off period until the next 7 hour heating cycle?
With a total thermal conductance G = 900 Btu/h-F and C = 66.7K Btu/h-F,
RC = C/G = 74 hours. If the house is 70 F at 7 AM on a 40 F day, it will
cool to 40+(70-40)exp(-17/74) = 64 after 17 hours.
>I'm guessing the 7kW would be fine - however our own calculations for
>room by room heat loss indicate that we need much more than this (but
>this is using standard calculations designed for standard houses!)
The heat pump power requirement depends more on conductance than mass.
The example needs about (70-40)900 = 27K Btu/h (8 kW) to stay 70 F
on a 30 F day...
Nick
Gareth Jones
<ni...@acadia.ee.vill.edu> writes
>
>With a total thermal conductance G = 900 Btu/h-F and C = 66.7K Btu/h-F,
>RC = C/G = 74 hours. If the house is 70 F at 7 AM on a 40 F day, it will
>cool to 40+(70-40)exp(-17/74) = 64 after 17 hours.
>
>
>The heat pump power requirement depends more on conductance than mass.
>The example needs about (70-40)900 = 27K Btu/h (8 kW) to stay 70 F
>on a 30 F day...
>
These sound about the most realistic figures I've seen so far.
I'll sit and digest them and see what implications they have.
A drop of 6 F would mean its going to be a bit chilly going to bed ;-)
As the ground floor has already been built, there's not much I can
change there - but maybe extra insulation in the roof might be prudent.
But at least my proposed 11kW heat pump might have a chance.....
Thanks!
Abby Normal
If it is slab on grade it would be advisable to insulate the perimeter of
the slab. You may want to extend this perimeter insulation down below grade.
GerryFerns
gareth@_ns_swansea.demon.co.uk wrote on 1/24/01 6:04 AM:
> In article <94i841$g...@acadia.ee.vill.edu>, Nick Pine
> <ni...@acadia.ee.vill.edu> writes
>>
>> With a total thermal conductance G = 900 Btu/h-F and C = 66.7K Btu/h-F,
>> RC = C/G = 74 hours. If the house is 70 F at 7 AM on a 40 F day, it will
>> cool to 40+(70-40)exp(-17/74) = 64 after 17 hours.
>>
>>
>
>> The heat pump power requirement depends more on conductance than mass.
>> The example needs about (70-40)900 = 27K Btu/h (8 kW) to stay 70 F
>> on a 30 F day...
>>
>
> These sound about the most realistic figures I've seen so far.
> I'll sit and digest them and see what implications they have.
> A drop of 6 F would mean its going to be a bit chilly going to bed ;-)
>
> As the ground floor has already been built, there's not much I can
> change there - but maybe extra insulation in the roof might be prudent.
>
> But at least my proposed 11kW heat pump might have a chance.....
>
> Thanks!
The capacity of the ground source unit should be based upon the anticipated
entering loop temperature, (ELT), at the end of the heating season. In
summer the loop will return to ground temperature.
In the Great White North of Canada, we generally see closed loop
temperatures bottom out at 16 to 20 degrees F. below the average soil
temperature by the middle of Feb.
Select your capacity similarly if you don't want to use auxiliary heat in
the coldest part of winter.
An extended range unit designed for 30 degree F ELT is required for
durability.
Depending somewhat upon internal gains, solar gains and construction
quality, has been shown that over and over that buildings require less heat
over a year than is indicated by single measure calculations such as degree
days and heat loss alone.
Assuming an 8 kW. Heat loss, a fraction of the design load, probably around
5 kW. of capacity, (at the average soil temperature minus 16 to 20 degrees
F., ELT), probably somewhere around 30 degree F. will be required to satisfy
99.9% of the annual Btu's.
Use a suitable antifreeze to protect your unit. A de-natured ethyl alcohol
is the "LoopSolution" of choice here.
Also the Entering Load Water Temperature, (hydronics side), affects capacity
and COP directly so maximizing the potential of the unit by using an outdoor
temperature, reset water temperature controller is recommended.
Does your manufacturer have software to size the loop for your contractor,
they should.
I can assist you in this matter if you require this.
Regards,
Gerry Ferns,
NextEnergy Solutions,
Renewable Energy Division
a_bee_...@my-deja.com
> The capacity of the ground source unit should be based upon the
anticipated
> entering loop temperature, (ELT), at the end of the heating season.
In
> summer the loop will return to ground temperature.
I would base the capacity of a ground source hea pump on the loop
temperature expected in Late January or early Feb when you could expect
to be at the design ambient
> In the Great White North of Canada, we generally see closed loop
> temperatures bottom out at 16 to 20 degrees F. below the average soil
> temperature by the middle of Feb.
Ground temp of 16F , where are you Tuktoyatik or Iqaluit?
I grew up in Thunder Bay and the only people who can tell me I was not
from the great white north were those in MB, Sask or the NWT's. I am
talking 10,000 plus F degree Days and an ambient design temp lower than
-30C.
I have never seen a ground loop bottom out at 16 or 20 F. Worst case I
ever measured was 29F. Are you installing loops under plowed parking
lots?
The coldest loop temperatures will occur in late March or Early April
however the heat load experienced in this time frame will not be as
great as will be experienced in Jan or Feb.
> Select your capacity similarly if you don't want to use auxiliary
heat in
> the coldest part of winter.
>
> An extended range unit designed for 30 degree F ELT is required for
> durability.
I would say select a unit to due 75 to 80% of the heat load at design
ambient conditions based on an EWT (ELT) of 30 or 32 F.
True ethanol is the antifreeze of choice, however your numbers suggest
to me that you are replying based on something you have read in books.
I have never witnesssed a loop in Canada to fall significantly below
the freezing point of water.
Sent via Deja.com
http://www.deja.com/
Tom Beckner
<a_bee_...@my-deja.com> wrote in message
news:94tjg4$4ei$1...@nnrp1.deja.com...
> > In the Great White North of Canada, we generally see closed loop
> > temperatures bottom out at 16 to 20 degrees F. below the average soil
> > temperature by the middle of Feb.
>
> Ground temp of 16F , where are you Tuktoyatik or Iqaluit?
This here is what you call a reading comprehension problem.
Maybe mine, I don't know.
Tom Beckner
Abby Normal
insulting. You stated that the ELT would be 16 to 20F below the 'Average
Soil Temperature' not that it was the soil temperature. Again, my apologies.
GerryFerns <gerry...@look.ca> wrote in message
news:B6964DBD.781%gerry...@look.ca...
> in article hCC9TAA1...@swansea.demon.co.uk, Gareth Jones at
> gareth@_ns_swansea.demon.co.uk wrote on 1/24/01 6:04 AM:
>
> The capacity of the ground source unit should be based upon the
anticipated
> entering loop temperature, (ELT), at the end of the heating season. In
> summer the loop will return to ground temperature.
>
> In the Great White North of Canada, we generally see closed loop
> temperatures bottom out at 16 to 20 degrees F. below the average soil
> temperature by the middle of Feb.
In Canada, I believe the loop temperature is related to the freezing point
of water rather than average soil temperature. 32 + 16 = 48 and 32 + 20 =
52. I would say that freezing of water is the limiting factor.
Having grown up in the North, I do not consider Toronto the Great White
North but rather the banana belt. Snow cover and the latent heat of soil
moisture and moisture migration tend to make a few degrees below the
freezing point of water an asymptote that the loop temperatures will
approach.
Early in the heating season the ground is quite warm and you have high
ELT's, as you progress into the heating season the loop temperature drops.
Consider December and the heating system is perhaps running for long periods
of time without using auxiliary heat. It could very well be running for a 40
minute cycle. At the beginning of the heat cycle, the ELT could be say 36F.
As the heat cycle progresses, this ELT will slowly drop and could fall below
freezing suggesting that some frost is being formed around the loop. The
unit cycles off for ten minutes and then comes back on. The Loop temperature
is now above freezing again, probably back to about 36F. To me this suggests
that sensible heat from the surrounding earth has conducted towards the
loop, and thawed out the frost that was forming. Perhaps some small amount
of moisture has migrated to the cold 'line' in the soil bringing with it
some sensible and latent heat.
I would estimate that by mid January, there is 'permfrost' forming around
the loop that will not thaw out until after the heating season. This frost
will actually increase conductivity around the loop as frozen soil is more
conductive than thawed soil, based on the conductivity of water vs ice. At
this point, the loop temperature will be hovering just below freezing. I
think the majority of heat that a heat pump absorbs is latent heat.
With the loop hovering around freezing, the selection of a unit based on a
30F ELT is pratical.
The lowest loop temperature will be in early spring, just before the snow
melts due to this is when the 'ring of frost' around the loop would be at
its thickest; however the heat demand, is not the same as the first week of
February so an ELT of a few degrees below design will not facilitate the
need for auxiliary heat..
> Select your capacity similarly if you don't want to use auxiliary heat in
> the coldest part of winter.
>
> An extended range unit designed for 30 degree F ELT is required for
> durability.
> Depending somewhat upon internal gains, solar gains and construction
> quality, has been shown that over and over that buildings require less
heat
> over a year than is indicated by single measure calculations such as
degree
> days and heat loss alone.
Sounds like you were trained by Water Furnace, in my opinion, the balance
point method is a ploy to increase the sales of GSHPs. It undersizes
equipment, and smaller units with shorter loops are less expensive to
install. Therefore a lower price will increase GSHP sales over straight
electric or fossil fuel alternatives in areas not serviced by natural gas.
Not much solar gain at 3 AM when its -30C outside. I would go for 75 to 80%
of the design loss. Larger than that and I feel you are into diminishing
returns.
>
> Assuming an 8 kW. Heat loss, a fraction of the design load, probably
around
> 5 kW. of capacity, (at the average soil temperature minus 16 to 20 degrees
> F., ELT), probably somewhere around 30 degree F. will be required to
satisfy
> 99.9% of the annual Btu's.
>
> Use a suitable antifreeze to protect your unit. A de-natured ethyl
alcohol
> is the "LoopSolution" of choice here.
>
> Also the Entering Load Water Temperature, (hydronics side), affects
capacity
> and COP directly so maximizing the potential of the unit by using an
outdoor
> temperature, reset water temperature controller is recommended.
For radiant floor I think he should use a buffer tank and a mixing valve. I
agree that you do not want the GSHP trying to make hot water. For his floor
heating system, it depends on how it was laid out but I do not think that in
the UK he will need water tempertures much higher than 85F or 90F out of the
mixing valve. Could reset the buffer tank temperature up and down with the
outdoor ambient.
> Does your manufacturer have software to size the loop for your contractor,
> they should.
In the original poster's situation, I think it would be a good idea if the
manufacturer sized the loop. If as the poster claims it is a newly applied
technology in the UK, then a manufacturer's rep should be on hand to
supervise or show the contractor how to do the instalation. The manufacturer
should also be able to project the difference in the installation cost vs
operating costs of the various size units the original poster was
considering.
ClimateMaster used to babysit all my former competitors through their first
installs back in the late 80's, prior to the days of the old CEEA. Climate
Master also was recommending the shortest loops I had ever seen in Canada,
with too much reliance on latent heat.
Nick Pine
>...I would say that freezing of water is the limiting factor... Snow cover
>and the latent heat of soil moisture and moisture migration tend to make
>a few degrees below the freezing point of water an asymptote that the loop
>temperatures will approach...
Hmmm.
>I would estimate that by mid January, there is 'permfrost' forming around
>the loop that will not thaw out until after the heating season. This frost
>will actually increase conductivity around the loop as frozen soil is more
>conductive than thawed soil, based on the conductivity of water vs ice. At
>this point, the loop temperature will be hovering just below freezing. I
>think the majority of heat that a heat pump absorbs is latent heat... With
>the loop hovering around freezing, the selection of a unit based on a
>30F ELT is pratical.
How about making the loop a hose containing antifreeze in a big water tank?
Wasn't there a system with an acronym like ACES that made ice in the winter
and used it for AC in summer? With a COP close to 3?
We might freeze a $500 24' diameter x 4' deep 15K gallon swimming pool
solid with 15Kx8x144 = 16.7M Btu, enough heat for a month or two.
It might have a solar pool cover...
Nick
Abby Normal
apologize below
Gareth Jones
<a_bee_normal@spam_yahoo.com> writes
>For radiant floor I think he should use a buffer tank and a mixing valve.
I've been thinking about this. As I'm hoping to run the heat pump mainly
in the night, the buffer tank would help smooth out the heating profile,
but I've seen nothing in the UK giving me details of prices or
installation methods (this to me means its gonna be expensive and I
ain't got no money left!!!)
Anyone care to give me an idea of ways of achieving this?
> I
>agree that you do not want the GSHP trying to make hot water.
I'll have to go back and read the last post... remind me why?? It would
be great if I could - or at least pre-heat the water.
> For his floor
>heating system, it depends on how it was laid out but I do not think that in
>the UK he will need water tempertures much higher than 85F or 90F out of the
>mixing valve.
The unit we have in mind has a 50C output.
>> Does your manufacturer have software to size the loop for your contractor,
>> they should.
>
>In the original poster's situation, I think it would be a good idea if the
>manufacturer sized the loop. If as the poster claims it is a newly applied
>technology in the UK, then a manufacturer's rep should be on hand to
>supervise or show the contractor how to do the instalation.
The manufacturer of the system will in fact install and commission it.
They did send a representative out last week to check soil conditions
and have quoted 450m of loop buried at least 4ft deep for their 11kW HP.
We get frost where we are, but its an abnormal winter if it freezes the
ground for deeper than about 5-6 inches, and then I guess its for a
couple of weeks if its a bad year! .... It just rains here a lot :-(
Abby Normal
Gareth Jones wrote in message ...
>In article <98060961...@RedRat.CandW.ky>, Abby Normal
><a_bee_normal@spam_yahoo.com> writes
>>For radiant floor I think he should use a buffer tank and a mixing valve.
>
>I've been thinking about this. As I'm hoping to run the heat pump mainly
>in the night, the buffer tank would help smooth out the heating profile,
>but I've seen nothing in the UK giving me details of prices or
>installation methods (this to me means its gonna be expensive and I
>ain't got no money left!!!)
>Anyone care to give me an idea of ways of achieving this?
>
>> I
>>agree that you do not want the GSHP trying to make hot water.
My post was misleading. Nothing wrong with making domestic hot water. You
don't want it pushing 50C or higher all the time when you are heating your
house. The hotter the water, the higher the head pressure, and the more
electricity you will consume. Gerry's post referred to this and he suggested
an outdoor reset to control how hot the heating loop water would be.
You can do partial domestic hot water using a desuperheater or you can get
on demand models, that will divert their entire heat output into domestic
hot water production.
>
>I'll have to go back and read the last post... remind me why?? It would
>be great if I could - or at least pre-heat the water.
>
>
>> For his floor
>>heating system, it depends on how it was laid out but I do not think that
in
>>the UK he will need water tempertures much higher than 85F or 90F out of
the
>>mixing valve.
The required water temperature that the radiant floor requires could be in
the 85 or 90F range. I can't say for sure as I did not design the tubing
layout. The buffer tank I mentioned would be heated by the heat pump. Your
floor won't need 50C, it will require a lower temp. The circulator that
supplies the water to the floor can draw water from a mixing valve, that you
set for a certain temperature. The valve mixes hot water from the buffer
tank with some of the return water coming back from the floor to supply 85
or 90F water to the floor.
>The unit we have in mind has a 50C output.
>
>>> Does your manufacturer have software to size the loop for your
contractor,
>>> they should.
>>
>>In the original poster's situation, I think it would be a good idea if the
>>manufacturer sized the loop. If as the poster claims it is a newly applied
>>technology in the UK, then a manufacturer's rep should be on hand to
>>supervise or show the contractor how to do the instalation.
>
>The manufacturer of the system will in fact install and commission it.
>They did send a representative out last week to check soil conditions
>and have quoted 450m of loop buried at least 4ft deep for their 11kW HP.
>We get frost where we are, but its an abnormal winter if it freezes the
>ground for deeper than about 5-6 inches, and then I guess its for a
>couple of weeks if its a bad year! .... It just rains here a lot :-(
Thats about 1500 feet. Is it 450m of pipe in 450m of trench? At what ELT is
the 11KW rating taken at?
Abby Normal
Nick Pine wrote in message <94uvtq$e...@ufo.ee.vill.edu>...
>We might freeze a $500 24' diameter x 4' deep 15K gallon swimming pool
>solid with 15Kx8x144 = 16.7M Btu, enough heat for a month or two.
>It might have a solar pool cover...
I guess anything is possible but you would have to have a cistern below
ground to be insulated from the elements. Need a bigger, heavy duty cistern
for 10,000 plus degree days, more like 30000 kwh for a cold Canadian winter.
Have to have room for ice expansion, I think it would be cheaper to dig
trenches and install the loops than it would be to bury 5 swimming pools a
few feet below grade.
Nick Pine
>>We might freeze a $500 24' diameter x 4' deep 15K gallon swimming pool
>>solid with 15Kx8x144 = 16.7M Btu, enough heat for a month or two.
>>It might have a solar pool cover...
>I guess anything is possible but you would have to have a cistern below
I'm not sure about that. Exposing the top to the sun and the bottom to
warmer earth seems useful. The sides don't have much surface compared
to the top and bottom, but they might have R10 foamboard insulation.
>Need a bigger, heavy duty cistern for 10,000 plus degree days...
Maybe not, if the sun shines in the winter. International Falls, MN has
10487 DD, with a 36.8 F deep ground temp. The average air temp is 7.2 in
December, and 750 Btu/ft^2-day of sun falls on a south wall, with 350 on
a horizontal surface. Say a 400 Btu/h-F house sucks 30d24h(70-7.2)400
= 18.1M Btu out of the pool, and it gains 30x450ft^2x0.9x350 = 4.2M from
the sun and loses 30dx24h(32-7.2)450ft^2/R1 = 8M to the air...
Well, maybe the pool needs a reflector, eg a white semi-cylinder 12' above
the south wall that adds 5.8M Btu in December. Then again, maybe the house
keeps itself warm on an average December day, with an average amount of sun,
and the pool only supplies DHW and cloudy day heat...
Nick
Tom Beckner
Abby Normal <a_bee_normal@spam_yahoo.com> wrote in message
news:98063261...@RedRat.CandW.ky...
> Called shouldn't read after being at the pub, place foot in mouth and
> apologize below
Why didn't you say so? Pub Speed Reading is Ok.
Tom Beckner
Gareth Jones
<a_bee_...@spamyahoo.com> writes
>>The manufacturer of the system will in fact install and commission it.
>>They did send a representative out last week to check soil conditions
>>and have quoted 450m of loop buried at least 4ft deep for their 11kW HP.
>>We get frost where we are, but its an abnormal winter if it freezes the
>>ground for deeper than about 5-6 inches, and then I guess its for a
>>couple of weeks if its a bad year! .... It just rains here a lot :-(
>
>
>Thats about 1500 feet. Is it 450m of pipe in 450m of trench? At what ELT is
>the 11KW rating taken at?
450m pipe in about 100m of trench which is 3ft wide
Don't know about the ELT question.
Abby Normal
>
> 450m pipe in about 100m of trench which is 3ft wide
Is it a 6 foot deep trench with pipes at the 4' and 6' level perhaps?
> Don't know about the ELT question.
The heat output of the heat pump varies with the Entering Loop Temperature.
For example I was wondering if your 11 KW heat rating was based on a high
ELT, say pushing 10C?
What is a cold day there, -5C?
Gareth Jones
<a_bee_normal@spam_yahoo.com> writes
>
>>
>> 450m pipe in about 100m of trench which is 3ft wide
>Is it a 'slinky' type of piping, like a crokscrew?
Probably, but not definitely. The 'other' UK GLHP company certainly does
use this method.
>
>Is it a 6 foot deep trench with pipes at the 4' and 6' level perhaps?
No, just 4'
>
>> Don't know about the ELT question.
>
>The heat output of the heat pump varies with the Entering Loop Temperature.
>For example I was wondering if your 11 KW heat rating was based on a high
>ELT, say pushing 10C?
>
>What is a cold day there, -5C?
About that. We had a week of very cold weather around Xmas (you know,
brought the whole country to a standstill.....) I had a temp sensor
dangling out of the trailer we are living in while we build and -5C was
the lowest it went. Mind you, some parts of the UK were supposed to have
-12C. But then some years it hardly freezes at all!
Abby Normal
Nick Pine wrote in message <950qsk$e...@ufo.ee.vill.edu>...
>I'm not sure about that. Exposing the top to the sun and the bottom to
>warmer earth seems useful. The sides don't have much surface compared
>to the top and bottom, but they might have R10 foamboard insulation.
>
>>Need a bigger, heavy duty cistern for 10,000 plus degree days...
>
>Maybe not, if the sun shines in the winter. International Falls, MN has
>10487 DD, with a 36.8 F deep ground temp.
Sounds right
>The average air temp is 7.2 in
>December, and 750 Btu/ft^2-day of sun falls on a south wall, with 350 on
>a horizontal surface. Say a 400 Btu/h-F house sucks 30d24h(70-7.2)400
>= 18.1M Btu out of the pool, and it gains 30x450ft^2x0.9x350 = 4.2M from
>the sun and loses 30dx24h(32-7.2)450ft^2/R1 = 8M to the air...
Average could be 7F, but there is also -40F. Ice would form at the surface
as fast as it formed around the loop.
Back to digging the trench and burying pipe.
No way to work solar in here. Accept the fact that a ground source heat pump
is already a solar collector system combined with thermal storage. The earth
is the collector that thaws out the frozen storage medium each spring.
In the UK, or more southerly states maybe it is more of a sensible heat
process but in Frostbite Falls MN and points north it is latent.
There are a few loops anchored to the bottom of Rainy Lake on both sides of
the border. Sort of a natural, large scale version of your swimming pool
theory.
Abby Normal
Gareth Jones <gareth@_ns_swansea.demon.co.uk> wrote in message
news:OgyWbIAt...@swansea.demon.co.uk...
> In article <98069797...@RedRat.CandW.ky>, Abby Normal
> <a_bee_normal@spam_yahoo.com> writes
> >
> >>
> >> 450m pipe in about 100m of trench which is 3ft wide
> >Is it a 'slinky' type of piping, like a crokscrew?
>
> Probably, but not definitely. The 'other' UK GLHP company certainly does
> use this method.
>
> >
> >Is it a 6 foot deep trench with pipes at the 4' and 6' level perhaps?
>
> No, just 4'
Get the ground loop and circ pump designed by the heat pump manufacturer.
You want the flow in the loop to be turbulent not laminar. The loop sounds
short to me but if a week of -5C is the extent of your winter then I it
should be fine. Where I grew up, -5C is a mild winter day or an
overnight low in April.
GerryFerns
a_bee_normal@spam_yahoo.com wrote on 1/27/01 10:45 AM:
> Sorry Gerry, I should read your whole post carefully before I rant and get
> insulting. You stated that the ELT would be 16 to 20F below the 'Average
> Soil Temperature' not that it was the soil temperature. Again, my apologies.
A loop operating at 16 to 20 degree below average soil temp appears to be
true right across Canada when following the industry accepted loop lengths,
i.e., 500 ft per ton of unit cooling capacity, 1.25" diameter pipe, 2 pipes
per trench.
Soil moisture content affects the 4 degree variance as I have occasionally
seen loops run down to 25 degrees F. in dry sand in S. Ontario.
> In Canada, I believe the loop temperature is related to the freezing point
> of water rather than average soil temperature. 32 + 16 = 48 and 32 + 20 =
> 52. I would say that freezing of water is the limiting factor.
25% ethanol solution is the loop juice of choice to provide anti-freeze
protection in Ontario and Methanol solution is often used outside Ontario
even though it is toxic.
> Early in the heating season the ground is quite warm and you have high
> ELT's, as you progress into the heating season the loop temperature drops.
> Consider December and the heating system is perhaps running for long periods
> of time without using auxiliary heat. It could very well be running for a 40
> minute cycle. At the beginning of the heat cycle, the ELT could be say 36F.
> As the heat cycle progresses, this ELT will slowly drop and could fall below
> freezing suggesting that some frost is being formed around the loop. The
> unit cycles off for ten minutes and then comes back on. The Loop temperature
> is now above freezing again, probably back to about 36F. To me this suggests
> that sensible heat from the surrounding earth has conducted towards the
> loop, and thawed out the frost that was forming. Perhaps some small amount
> of moisture has migrated to the cold 'line' in the soil bringing with it
> some sensible and latent heat.
This is an interesting observation isn't it. It answers the question when
does a loop recover heat -- whenever there is a temperature difference
between the loop and the ground.
> I would estimate that by mid January, there is 'permfrost' forming around
> the loop that will not thaw out until after the heating season. This frost
> will actually increase conductivity around the loop as frozen soil is more
> conductive than thawed soil, based on the conductivity of water vs ice. At
> this point, the loop temperature will be hovering just below freezing. I
> think the majority of heat that a heat pump absorbs is latent heat.
Latent heat of fusion of water does contribute heat to loops but it's affect
on delaying loop cooling varies across the country depending upon soil
moisture content, degree days and soil temps.
>
> With the loop hovering around freezing, the selection of a unit based on a
> 30F ELT is pratical.
If you install a loop in Manitoba, i.e., Winnipeg, using industry accepted
loop lengths we see loops running at 25 degrees F. or lower commonly. You
can add pipe till you run out of money but it doesn't change loop temps.
much at all. Average soil temp around Winnipeg is 43 degrees F.
> The lowest loop temperature will be in early spring, just before the snow
> melts due to this is when the 'ring of frost' around the loop would be at
> its thickest; however the heat demand, is not the same as the first week of
> February so an ELT of a few degrees below design will not facilitate the
> need for auxiliary heat..
Lowest loop temp will vary regionally depending on degree days. Here in
London, Ont. We just about always have a thaw for a week in late Jan or Feb.
after that moisture goes into the ground we never see loops close to
freezing for the rest of the season.
>
> Sounds like you were trained by Water Furnace, in my opinion, the balance
> point method is a ploy to increase the sales of GSHPs. It undersizes
> equipment, and smaller units with shorter loops are less expensive to
> install. Therefore a lower price will increase GSHP sales over straight
> electric or fossil fuel alternatives in areas not serviced by natural gas.
> Not much solar gain at 3 AM when its -30C outside. I would go for 75 to 80%
> of the design loss. Larger than that and I feel you are into diminishing
> returns.
The balance point method you mention is based upon the Modified Degree Day,
multiple measure energy analysis approach from ASHRAE Fundamentals,
WaterFurnace just adopted it. I believe that it is a valid approach if it
is applied honestly.
75 to 80% of the design loss is not appropriate for the entire country. It
will result in over sizing and perhaps short cycling in Southern Ontario, or
Vancouver or parts of the Maritimes. In parts of the country further North
than Thunder Bay, the system may still be under sized. A sophisticated
analysis of each application is required.
>
> For radiant floor I think he should use a buffer tank and a mixing valve. I
> agree that you do not want the GSHP trying to make hot water. For his floor
> heating system, it depends on how it was laid out but I do not think that in
> the UK he will need water tempertures much higher than 85F or 90F out of the
> mixing valve. Could reset the buffer tank temperature up and down with the
> outdoor ambient.
Good approach.
> In the original poster's situation, I think it would be a good idea if the
> manufacturer sized the loop. If as the poster claims it is a newly applied
> technology in the UK, then a manufacturer's rep should be on hand to
> supervise or show the contractor how to do the instalation. The manufacturer
> should also be able to project the difference in the installation cost vs
> operating costs of the various size units the original poster was
> considering.
You'd think so wouldn't you but some manufacturers just sell boxes.
> ClimateMaster used to babysit all my former competitors through their first
> installs back in the late 80's, prior to the days of the old CEEA. Climate
> Master also was recommending the shortest loops I had ever seen in Canada,
> with too much reliance on latent heat.
ClimateMaster now has very nice loop design software and a real commitment
to geothermal.
Gareth Jones
<a_bee_normal@spam_yahoo.com> writes
>
>Get the ground loop and circ pump designed by the heat pump manufacturer.
>You want the flow in the loop to be turbulent not laminar.
Sheessh..... I don't know enough about fluid mechanics to comment on
this, but if you've got a 30m run of pipe supplying the 450m ground
loop, how do you have any control on the flow profile other than
controlling the pump speed?
> The loop sounds
>short to me but if a week of -5C is the extent of your winter then I it
>should be fine.
<Smile>
One week of -5..... 51 weeks of 24C ...... perhaps not ;-)
But I'm sure you know what I mean, I've just glanced at the thermometer
and its 6.1C outside, 10.30pm, so not too bad.
Pity about the rain........
Sechler
> Sheessh..... I don't know enough about fluid mechanics to comment on
> this, but if you've got a 30m run of pipe supplying the 450m ground
> loop, how do you have any control on the flow profile other than
> controlling the pump speed?
By keeping the Reynolds # (a function of fluid velocity, viscosity, pipe
roughness, pipe diam) in the turbulent flow region for better heat transfer.
Velocity and pipe diam are key. Don't oversize pipe.
Joe
Abby Normal
What is the circulation rate of water/antifreeze, is it in the range of say
0.66 litres per second?
Nick Pine
>A loop operating at 16 to 20 degree below average soil temp appears to be
>true right across Canada when following the industry accepted loop lengths,
>i.e., 500 ft per ton of unit cooling capacity, 1.25" diameter pipe, 2 pipes
>per trench... Latent heat of fusion of water does contribute heat to loops.
Maybe you should also bury a soaker hose :-)
Nick
Tom Beckner
Nick Pine <ni...@ufo.ee.vill.edu> wrote in message
news:959e8e$f...@ufo.ee.vill.edu...
Discharge from sump pumps works, too.
Tom Beckner
pwate...@gmail.com
> <Posted from the alt.hvac group>
> Hi Folks,
> Although this is a posting from the UK, you US people seem to have a
> load of experience in this area so please don't let a small stretch of
> water put you off replying ;-)
>
> One question in two halves:
> heating system in the house I'm building. This is constructed from
> Pex pipe embedded in the top 2 inches. There is a fairly high degree of
> insulated dwelling (without going mad!).
> Because it has such a large mass (and all the internal walls are 4in
> run the heat pump. (Don't know if you have this outside the UK - its
> where you can use off peak power between midnight and 7am at about a
> third of the price).
> I could spend weeks doing research into all the co-efficients and trying
> to work out thermal mass and heat transfer calculations, but frankly,
> most of the time, an experienced HVAC engineer will have come across
> similar situations and will have a gut feeling about what can and can't
> be done.
> So I'm wondering, if you heat up the floors in the night, will the
> the 17hr off period until the next 7 hour heating cycle?
> as a backup ;-)
>
> Which leads me on to the second half of the question:
> I have located a supplier of heat pumps. There are three models in their
> range. They provide 4, 7 and 11kW outputs.
> The house is a reasonable size - say 5 bed, approx. 4000 sq ft. I've
> found a study on a similar property where they put in a 4kW GLHP. They
> calculated it would provide around 50% of their needs, but in reality
> provided 80%.
> So I'm guessing the 7kW would be fine - however our own calculations for
> this is using standard calculations designed for standard houses!)
> it uses a fair bit more juice (and also, the starting current is 111amps
> which worries me slightly!!). I'd rather use the 7kW if I could.
>
> Again, if anybody has experience in this area, I'd be very grateful for
> your comments.
> __________________________________________
> <Gareth Jones> usenet@_ns_swansea.demon.co.uk
>
> "Reality sucks - go watch a Star Trek"
>
> To email, remove the '_ns_' from
> usenet@_ns_swansea.demon.co.uk
> __________________________________________
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