geothermal solar thermal storage

[Jamie M]

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

cheers,
Jamie

 

[Rick C]

On Sunday, January 26, 2020 at 8:33:15 PM UTC-5, Jamie M wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

cheers,
Jamie

Interesting. They only give the barest of details on how much energy they expect to provide to the homes. I believe they said the homes are constructed to use 30% less energy and the solar heating system is expected to provide 90% of that. I believe they mentioned a total power output of the garages, 1.5 MW. They don't say how many homes/garages that is for. Google maps show 52 homes, so 29 kW per home. Obviously that's a peak number, I wonder what the factor is to get an average energy use per home?

The most interesting part is the seasonal storage of heat in the borehole storage system. I'm surprised that can work efficiently over the winter. They don't talk at all about the storage capacity. Still, interesting claims.

The homes have to be oriented to the sun, so rectilinear layout. They stand out in a larger community with the typical curved streets and varied orientations.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

cheers,
Jamie

That's an insane amount of hardware to heat 52 homes. I wonder who is
paying for this "energy showcase."




--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

 

[Jamie M]

On 2020-01-26 6:53 p.m., Rick C wrote:

The most interesting part is the seasonal storage of heat in the borehole storage system. I'm surprised that can work efficiently over the winter. They don't talk at all about the storage capacity. Still, interesting claims.

The efficiency should go up with the effective volume (and storage
capacity) of the thermal battery, as there would be a smaller fraction
of heat lost (volume to surface area ratio).

One problem could be underground water flow, which could take a lot of
heat out of the thermal battery. Putting the battery in a place that
has a low year round water table would be necessary I guess.

Having deeper bore holes might be a way to reduce the required
insulation on the surface, ie since the surface is only about 1/6th of
the surface area of the thermal battery, there is not a lot to be gained
by insulating the surface rather than just increasing the depth of the
boreholes and depth of the thermal battery.

Also the type of solar collectors could be different, maybe it is
cheaper to use mirrors and a heating tower etc.

cheers,
Jamie

 

[Rick C]

On Sunday, January 26, 2020 at 11:09:44 PM UTC-5, Jamie M wrote:

On 2020-01-26 6:53 p.m., Rick C wrote:

The most interesting part is the seasonal storage of heat in the borehole storage system. I'm surprised that can work efficiently over the winter.. They don't talk at all about the storage capacity. Still, interesting claims.


The efficiency should go up with the effective volume (and storage
capacity) of the thermal battery, as there would be a smaller fraction
of heat lost (volume to surface area ratio).

That goes without saying, but even so, I'm surprised this could store heat from summer to winter. That's a lot of heat and a lot of time.

One problem could be underground water flow, which could take a lot of
heat out of the thermal battery. Putting the battery in a place that
has a low year round water table would be necessary I guess.

Sure, again that goes without saying. 100 foot wide and 115 feet deep. That's a lot of thermal mass. I'm just surprised it is large enough to store heat for a winter. But I'm sure they've done their homework.

Having deeper bore holes might be a way to reduce the required
insulation on the surface, ie since the surface is only about 1/6th of
the surface area of the thermal battery, there is not a lot to be gained
by insulating the surface rather than just increasing the depth of the
boreholes and depth of the thermal battery.

I would expect that unless there is a limit on land used, they would try to minimize the surface area by keeping the volume close to round. Notice they cut the corners from the bore hole pattern. I'm sure they insulated the surface rather than just burying the whole thing in more dirt because that is the most economical.

Also the type of solar collectors could be different, maybe it is
cheaper to use mirrors and a heating tower etc.

It's a community. Aesthetics!

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Jamie M]

On 2020-01-26 9:26 p.m., Rick C wrote:

On Sunday, January 26, 2020 at 11:09:44 PM UTC-5, Jamie M wrote:
On 2020-01-26 6:53 p.m., Rick C wrote:

The most interesting part is the seasonal storage of heat in the borehole storage system. I'm surprised that can work efficiently over the winter. They don't talk at all about the storage capacity. Still, interesting claims.


The efficiency should go up with the effective volume (and storage
capacity) of the thermal battery, as there would be a smaller fraction
of heat lost (volume to surface area ratio).

That goes without saying, but even so, I'm surprised this could store heat from summer to winter. That's a lot of heat and a lot of time.


One problem could be underground water flow, which could take a lot of
heat out of the thermal battery. Putting the battery in a place that
has a low year round water table would be necessary I guess.

Sure, again that goes without saying. 100 foot wide and 115 feet deep. That's a lot of thermal mass. I'm just surprised it is large enough to store heat for a winter. But I'm sure they've done their homework.


Having deeper bore holes might be a way to reduce the required
insulation on the surface, ie since the surface is only about 1/6th of
the surface area of the thermal battery, there is not a lot to be gained
by insulating the surface rather than just increasing the depth of the
boreholes and depth of the thermal battery.

I would expect that unless there is a limit on land used, they would try to minimize the surface area by keeping the volume close to round. Notice they cut the corners from the bore hole pattern. I'm sure they insulated the surface rather than just burying the whole thing in more dirt because that is the most economical.


Also the type of solar collectors could be different, maybe it is
cheaper to use mirrors and a heating tower etc.

It's a community. Aesthetics!

This is probably the solar collector (800 of them for 52 houses, about
15 panels per house) used:

https://enerworks.com/downloads/Heat-Safe-Collector.pdf

They are flat plate collectors, not the evacuated tube type.

https://en.wikipedia.org/wiki/Solar_thermal_collector#Comparisons_of_flat_plate_and_evacuated_tube_collectors
I agree it is a bit surprising the thermal mass per house, ie if the
thermal battery is a 100foot sphere for 52 houses, then that would
require a 13.4foot sphere for a single house. This smaller
sphere would have to be heavily insulated to have the same efficiency as
the larger thermal mass.

cheers,
Jamie

 

[Jamie M]

On 2020-01-26 9:53 p.m., upsidedown@downunder.com wrote:

On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

What so special about this ? There are a lot ground loop heat pump
installation, in which a large ground loop is installed 1-2 m below
ground in the garden. While some people call this "geothermal" but it
is just seasonal storage. The ground is heated in the summer and that
heath energy is extracted in the winter. The snow cover in the winter
reduces the heat loss directly from the ground.

Hi,

The thermal battery with solar collectors doesn't require a heat pump as
long as the thermal battery temperature is high enough, 80 Celcius max
temperature at the start of winter, and maybe the thermal battery is at
30Celcius by the end of winter.

cheers,
Jamie

If the garden is too small and too much heat is extracted from the
ground, the ground temperature may fall below 0 C, in the spring
freezing the ground and nothing will grow in the garden during the
early summer. Some house owners dump air condition heat in the summer
into the ground loop, melting the garden soil and enabling plant
growth. If a solar thermal collector is added to the system, it can be
used to heat the house earlier in the spring and also earlier dump
some heat into the ground loop, making it possible to start the
growing season earlier.

With a larger garden loop, there is not even a risk for freezing the
ground towards the spring.

"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

That is insane. If dumped into the soil, it dry up the soil
completely. If some wells drilled into the ground water that would be
a very bad idea, since the heat would flow away and may be illegal if
ground water is used for drinking water in the area.

,

 

On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

What so special about this ? There are a lot ground loop heat pump
installation, in which a large ground loop is installed 1-2 m below
ground in the garden. While some people call this "geothermal" but it
is just seasonal storage. The ground is heated in the summer and that
heath energy is extracted in the winter. The snow cover in the winter
reduces the heat loss directly from the ground.

If the garden is too small and too much heat is extracted from the
ground, the ground temperature may fall below 0 C, in the spring
freezing the ground and nothing will grow in the garden during the
early summer. Some house owners dump air condition heat in the summer
into the ground loop, melting the garden soil and enabling plant
growth. If a solar thermal collector is added to the system, it can be
used to heat the house earlier in the spring and also earlier dump
some heat into the ground loop, making it possible to start the
growing season earlier.

With a larger garden loop, there is not even a risk for freezing the
ground towards the spring.

"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

That is insane. If dumped into the soil, it dry up the soil
completely. If some wells drilled into the ground water that would be
a very bad idea, since the heat would flow away and may be illegal if
ground water is used for drinking water in the area.

,

 

[Rick C]

On Monday, January 27, 2020 at 12:53:28 AM UTC-5, upsid...@downunder.com wrote:

On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

What so special about this ? There are a lot ground loop heat pump
installation, in which a large ground loop is installed 1-2 m below
ground in the garden. While some people call this "geothermal" but it
is just seasonal storage. The ground is heated in the summer and that
heath energy is extracted in the winter. The snow cover in the winter
reduces the heat loss directly from the ground.

I've never heard anyone say heat pump geothermal is intended to store energy in the ground. Rather it uses the ground as a heat sink which is at a better temperature than the air which improves the efficiency of the heat pump. If the ground temperature changes much it would defeat the advantages of the constant temperature heat sink.

I also don't think the few feet of earth on top would be adequate insulation for seasons.

If the garden is too small and too much heat is extracted from the
ground, the ground temperature may fall below 0 C, in the spring
freezing the ground and nothing will grow in the garden during the
early summer. Some house owners dump air condition heat in the summer
into the ground loop, melting the garden soil and enabling plant
growth.

Why would the ground be frozen in the summer??? Around here the garden is growing earlier than the heat is turned off.

If a solar thermal collector is added to the system, it can be
used to heat the house earlier in the spring and also earlier dump
some heat into the ground loop, making it possible to start the
growing season earlier.

With a larger garden loop, there is not even a risk for freezing the
ground towards the spring.

"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

That is insane. If dumped into the soil, it dry up the soil
completely. If some wells drilled into the ground water that would be
a very bad idea, since the heat would flow away and may be illegal if
ground water is used for drinking water in the area.

Don't you think they've considered water???

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[Jamie M]

On 2020-01-27 12:47 a.m., Rick C wrote:

On Monday, January 27, 2020 at 12:59:06 AM UTC-5, Jamie M wrote:
On 2020-01-26 9:26 p.m., Rick C wrote:

On Sunday, January 26, 2020 at 11:09:44 PM UTC-5, Jamie M wrote:
On 2020-01-26 6:53 p.m., Rick C wrote:

The most interesting part is the seasonal storage of heat in the borehole storage system. I'm surprised that can work efficiently over the winter. They don't talk at all about the storage capacity. Still, interesting claims.


The efficiency should go up with the effective volume (and storage
capacity) of the thermal battery, as there would be a smaller fraction
of heat lost (volume to surface area ratio).

That goes without saying, but even so, I'm surprised this could store heat from summer to winter. That's a lot of heat and a lot of time.


One problem could be underground water flow, which could take a lot of
heat out of the thermal battery. Putting the battery in a place that
has a low year round water table would be necessary I guess.

Sure, again that goes without saying. 100 foot wide and 115 feet deep. That's a lot of thermal mass. I'm just surprised it is large enough to store heat for a winter. But I'm sure they've done their homework.


Having deeper bore holes might be a way to reduce the required
insulation on the surface, ie since the surface is only about 1/6th of
the surface area of the thermal battery, there is not a lot to be gained
by insulating the surface rather than just increasing the depth of the
boreholes and depth of the thermal battery.

I would expect that unless there is a limit on land used, they would try to minimize the surface area by keeping the volume close to round. Notice they cut the corners from the bore hole pattern. I'm sure they insulated the surface rather than just burying the whole thing in more dirt because that is the most economical.


Also the type of solar collectors could be different, maybe it is
cheaper to use mirrors and a heating tower etc.

It's a community. Aesthetics!


This is probably the solar collector (800 of them for 52 houses, about
15 panels per house) used:

https://enerworks.com/downloads/Heat-Safe-Collector.pdf

They are flat plate collectors, not the evacuated tube type.

https://en.wikipedia.org/wiki/Solar_thermal_collector#Comparisons_of_flat_plate_and_evacuated_tube_collectors
I agree it is a bit surprising the thermal mass per house, ie if the
thermal battery is a 100foot sphere for 52 houses, then that would
require a 13.4foot sphere for a single house.

I get a 26 foot sphere. Divide 100 feet by the cube root of 52 or 3.7.

Oops, that sounds correct, I forgot I was using radius.

This smaller
sphere would have to be heavily insulated to have the same efficiency as
the larger thermal mass.

There is going to be more loss for a smaller sphere no matter what. But why would you think this is a good solution for a single home? I expect this only works if you can apply an economy of scale.

What thermal loss would the 26 foot sphere have compared to a 100 foot
sphere? If it is within 2x or 3x, it is still interesting to consider
possibly, although a standard geothermal heat pump would be simpler and
cheaper.

For a single house maybe instead of 15 panels, 30 panels would be
required to account for larger thermal battery losses in a 26 foot
sphere. That is a large up front cost, but has some advantages by not
having a heat pump, also the solar collector panels could be cheaper
(molded plastic types) in the future or integrated into roof.

Also for a single home, having the thermal battery under the basement
of the house might increase the overall efficiency etc.

cheers,
Jamie




>

 

[Rick C]

On Monday, January 27, 2020 at 12:59:06 AM UTC-5, Jamie M wrote:

On 2020-01-26 9:26 p.m., Rick C wrote:

On Sunday, January 26, 2020 at 11:09:44 PM UTC-5, Jamie M wrote:
On 2020-01-26 6:53 p.m., Rick C wrote:

The most interesting part is the seasonal storage of heat in the borehole storage system. I'm surprised that can work efficiently over the winter. They don't talk at all about the storage capacity. Still, interesting claims.


The efficiency should go up with the effective volume (and storage
capacity) of the thermal battery, as there would be a smaller fraction
of heat lost (volume to surface area ratio).

That goes without saying, but even so, I'm surprised this could store heat from summer to winter. That's a lot of heat and a lot of time.


One problem could be underground water flow, which could take a lot of
heat out of the thermal battery. Putting the battery in a place that
has a low year round water table would be necessary I guess.

Sure, again that goes without saying. 100 foot wide and 115 feet deep. That's a lot of thermal mass. I'm just surprised it is large enough to store heat for a winter. But I'm sure they've done their homework.


Having deeper bore holes might be a way to reduce the required
insulation on the surface, ie since the surface is only about 1/6th of
the surface area of the thermal battery, there is not a lot to be gained
by insulating the surface rather than just increasing the depth of the
boreholes and depth of the thermal battery.

I would expect that unless there is a limit on land used, they would try to minimize the surface area by keeping the volume close to round. Notice they cut the corners from the bore hole pattern. I'm sure they insulated the surface rather than just burying the whole thing in more dirt because that is the most economical.


Also the type of solar collectors could be different, maybe it is
cheaper to use mirrors and a heating tower etc.

It's a community. Aesthetics!


This is probably the solar collector (800 of them for 52 houses, about
15 panels per house) used:

https://enerworks.com/downloads/Heat-Safe-Collector.pdf

They are flat plate collectors, not the evacuated tube type.

https://en.wikipedia.org/wiki/Solar_thermal_collector#Comparisons_of_flat_plate_and_evacuated_tube_collectors
I agree it is a bit surprising the thermal mass per house, ie if the
thermal battery is a 100foot sphere for 52 houses, then that would
require a 13.4foot sphere for a single house.

I get a 26 foot sphere. Divide 100 feet by the cube root of 52 or 3.7.

This smaller
sphere would have to be heavily insulated to have the same efficiency as
the larger thermal mass.

There is going to be more loss for a smaller sphere no matter what. But why would you think this is a good solution for a single home? I expect this only works if you can apply an economy of scale.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Jamie M]

On 2020-01-27 1:42 a.m., Jamie M wrote:

On 2020-01-27 12:47 a.m., Rick C wrote:
On Monday, January 27, 2020 at 12:59:06 AM UTC-5, Jamie M wrote:
On 2020-01-26 9:26 p.m., Rick C wrote:

On Sunday, January 26, 2020 at 11:09:44 PM UTC-5, Jamie M wrote:
On 2020-01-26 6:53 p.m., Rick C wrote:

The most interesting part is the seasonal storage of heat in the
borehole storage system.  I'm surprised that can work efficiently
over the winter.  They don't talk at all about the storage
capacity.  Still, interesting claims.


The efficiency should go up with the effective volume (and storage
capacity) of the thermal battery, as there would be a smaller fraction
of heat lost (volume to surface area ratio).

That goes without saying, but even so, I'm surprised this could
store heat from summer to winter.  That's a lot of heat and a lot of
time.


One problem could be underground water flow, which could take a lot of
heat out of the thermal battery.  Putting the battery in a place that
has a low year round water table would be necessary I guess.

Sure, again that goes without saying.  100 foot wide and 115 feet
deep.  That's a lot of thermal mass.  I'm just surprised it is large
enough to store heat for a winter.  But I'm sure they've done their
homework.


Having deeper bore holes might be a way to reduce the required
insulation on the surface, ie since the surface is only about 1/6th of
the surface area of the thermal battery, there is not a lot to be
gained
by insulating the surface rather than just increasing the depth of the
boreholes and depth of the thermal battery.

I would expect that unless there is a limit on land used, they would
try to minimize the surface area by keeping the volume close to
round.  Notice they cut the corners from the bore hole pattern.  I'm
sure they insulated the surface rather than just burying the whole
thing in more dirt because that is the most economical.


Also the type of solar collectors could be different, maybe it is
cheaper to use mirrors and a heating tower etc.

It's a community.  Aesthetics!


This is probably the solar collector (800 of them for 52 houses, about
15 panels per house) used:

https://enerworks.com/downloads/Heat-Safe-Collector.pdf

They are flat plate collectors, not the evacuated tube type.

https://en.wikipedia.org/wiki/Solar_thermal_collector#Comparisons_of_flat_plate_and_evacuated_tube_collectors

I agree it is a bit surprising the thermal mass per house, ie if the
thermal battery is a 100foot sphere for 52 houses, then that would
require a 13.4foot sphere for a single house.

I get a 26 foot sphere.  Divide 100 feet by the cube root of 52 or 3.7.

Oops, that sounds correct, I forgot I was using radius.



This smaller
sphere would have to be heavily insulated to have the same efficiency as
the larger thermal mass.

There is going to be more loss for a smaller sphere no matter what.
But why would you think this is a good solution for a single home?  I
expect this only works if you can apply an economy of scale.

Another way to do a single house more efficiently could be to lower the
thermal battery temperature and make it larger, ie instead of a 80
Celcius max, 26 foot diameter, it could be 50 Celcius max, ~35+ foot
diameter. This has a more shallow temperature gradient and also would
make the roof solar collectors more efficient to operate at a lower
temperature, so more heat could be pumped into the thermal battery.

The working fluid pump rate would have to be increased for winter
heating as the fluid temperature is lower, but as long as it stays
above 30C or so it should work.

cheers,
Jamie

What thermal loss would the 26 foot sphere have compared to a 100 foot
sphere?  If it is within 2x or 3x, it is still interesting to consider
possibly, although a standard geothermal heat pump would be simpler and
cheaper.

For a single house maybe instead of 15 panels, 30 panels would be
required to account for larger thermal battery losses in a 26 foot
sphere.  That is a large up front cost, but has some advantages by not
having a heat pump, also the solar collector panels could be cheaper
(molded plastic types) in the future or integrated into roof.

Also for a single home, having the thermal battery under the basement
of the house might increase the overall efficiency etc.

cheers,
Jamie

 

[Bill Sloman]

On Monday, January 27, 2020 at 7:39:49 PM UTC+11, Rick C wrote:

On Monday, January 27, 2020 at 12:53:28 AM UTC-5, upsid...@downunder.com wrote:
On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

What so special about this ? There are a lot ground loop heat pump
installation, in which a large ground loop is installed 1-2 m below
ground in the garden. While some people call this "geothermal" but it
is just seasonal storage. The ground is heated in the summer and that
heath energy is extracted in the winter. The snow cover in the winter
reduces the heat loss directly from the ground.

I've never heard anyone say heat pump geothermal is intended to store energy in the ground. Rather it uses the ground as a heat sink which is at a better temperature than the air which improves the efficiency of the heat pump. If the ground temperature changes much it would defeat the advantages of the constant temperature heat sink.

I also don't think the few feet of earth on top would be adequate insulation for seasons.

If I remember rightly, the temperature 45cm below the surface lags the seasons by six months (or 180 degrees) which is exactly what you want.

A few feet of earth would be a bit more than that ...

If the garden is too small and too much heat is extracted from the
ground, the ground temperature may fall below 0 C, in the spring
freezing the ground and nothing will grow in the garden during the
early summer.

A shallow-rooted plants would grow fine.

Some house owners dump air condition heat in the summer
into the ground loop, melting the garden soil and enabling plant
growth.

Why would the ground be frozen in the summer??? Around here the garden is growing earlier than the heat is turned off.

Finland is a chilly place.

If a solar thermal collector is added to the system, it can be
used to heat the house earlier in the spring and also earlier dump
some heat into the ground loop, making it possible to start the
growing season earlier.

With a larger garden loop, there is not even a risk for freezing the
ground towards the spring.

"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

That is insane. If dumped into the soil, it dry up the soil
completely.

Depends where the water table is. Getting the soil dry would be a neat trick in a lot of places - the water vapour would move down as well as up.

If some wells drilled into the ground water that would be
a very bad idea, since the heat would flow away and may be illegal if
ground water is used for drinking water in the area.

Don't you think they've considered water???

Bore water comes from quite a bit further down.

--
Bill Sloman, Sydney

 

Rick C <gnuarm.deletethisbit@gmail.com> wrote in
news:1f719ac5-a8e9-4307-b9e9-68190abf4e65@googlegroups.com:

I've never heard anyone say heat pump geothermal is intended to
store energy in the ground.

Geothermal is great except for being on unstable ground in most
cases.

I think a better choice for a heat boost to a steam system would be
the interior of a huge salt dome. They are very hot, and very stable.
It is like a huge golf tee the size of Everest buried in the ground.
Within its heart is a hot core.

Also, I suggested this nearly twenty years ago.

 

[Rick C]

On Monday, January 27, 2020 at 7:12:06 AM UTC-5, Bill Sloman wrote:

On Monday, January 27, 2020 at 7:39:49 PM UTC+11, Rick C wrote:
On Monday, January 27, 2020 at 12:53:28 AM UTC-5, upsid...@downunder.com wrote:
On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

What so special about this ? There are a lot ground loop heat pump
installation, in which a large ground loop is installed 1-2 m below
ground in the garden. While some people call this "geothermal" but it
is just seasonal storage. The ground is heated in the summer and that
heath energy is extracted in the winter. The snow cover in the winter
reduces the heat loss directly from the ground.

I've never heard anyone say heat pump geothermal is intended to store energy in the ground. Rather it uses the ground as a heat sink which is at a better temperature than the air which improves the efficiency of the heat pump. If the ground temperature changes much it would defeat the advantages of the constant temperature heat sink.

I also don't think the few feet of earth on top would be adequate insulation for seasons.

If I remember rightly, the temperature 45cm below the surface lags the seasons by six months (or 180 degrees) which is exactly what you want.

Not really. It is an irrelevant statistic. The issue at hand is heat loss.. The fact that the thermal losses in winter cause the temperature to turn around in mid winter is not the important aspect. Consider the amount of insulation that will cause that effect, then add more insulation and you have a better storage system even though the temperature peak is now a different time.


> A few feet of earth would be a bit more than that ...

And a better insulator.

If the garden is too small and too much heat is extracted from the
ground, the ground temperature may fall below 0 C, in the spring
freezing the ground and nothing will grow in the garden during the
early summer.

A shallow-rooted plants would grow fine.

Some house owners dump air condition heat in the summer
into the ground loop, melting the garden soil and enabling plant
growth.

Why would the ground be frozen in the summer??? Around here the garden is growing earlier than the heat is turned off.

Finland is a chilly place.

Non sequitur. Now you sound like JL.

--

Rick C.

++ Get 1,000 miles of free Supercharging
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[Rick C]

On Monday, January 27, 2020 at 4:42:15 AM UTC-5, Jamie M wrote:

On 2020-01-27 12:47 a.m., Rick C wrote:
On Monday, January 27, 2020 at 12:59:06 AM UTC-5, Jamie M wrote:

This is probably the solar collector (800 of them for 52 houses, about
15 panels per house) used:

https://enerworks.com/downloads/Heat-Safe-Collector.pdf

They are flat plate collectors, not the evacuated tube type.

https://en.wikipedia.org/wiki/Solar_thermal_collector#Comparisons_of_flat_plate_and_evacuated_tube_collectors
I agree it is a bit surprising the thermal mass per house, ie if the
thermal battery is a 100foot sphere for 52 houses, then that would
require a 13.4foot sphere for a single house.

I get a 26 foot sphere. Divide 100 feet by the cube root of 52 or 3.7.

Oops, that sounds correct, I forgot I was using radius.



This smaller
sphere would have to be heavily insulated to have the same efficiency as
the larger thermal mass.

There is going to be more loss for a smaller sphere no matter what. But why would you think this is a good solution for a single home? I expect this only works if you can apply an economy of scale.

What thermal loss would the 26 foot sphere have compared to a 100 foot
sphere? If it is within 2x or 3x, it is still interesting to consider
possibly, although a standard geothermal heat pump would be simpler and
cheaper.

The thermal loss would be proportionally 3.7 times larger than the 100 foot sphere assuming all losses are relative to the surface area.

A geothermal heat pump will save money, but it won't reduce the energy consumption by 90%. That's an impressive number. With the emphasis on reducing the carbon footprint it's ironic that they burn gas as the backup heat for the 10%. I'm not sure if a geothermal unit will even cut your electric use by 50%. It is supposed to pay for itself.

For a single house maybe instead of 15 panels, 30 panels would be
required to account for larger thermal battery losses in a 26 foot
sphere. That is a large up front cost, but has some advantages by not
having a heat pump, also the solar collector panels could be cheaper
(molded plastic types) in the future or integrated into roof.

I don't know how expensive the thermal collection panels are. I have always heard that solar hot water is a better financial proposition than solar PV, but that likely has been mitigated by the relatively recent reductions in cost of solar PV.

Also for a single home, having the thermal battery under the basement
of the house might increase the overall efficiency etc.

Not if you ever need to dig it up for repair!

I think to get seasonal storage of energy it would require both more solar collectors and a larger size of the bore hole storage system. Double the collectors and you likely need to double the capacity of the storage, or 25% larger diameter than we figured before, 34 feet now.

I just did a calculation and in winter my roof pitch is 16.6° off the angle of the sun and in summer it is 30.4° off. That is not bad.

--

Rick C.

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[George Herold]

On Monday, January 27, 2020 at 12:53:28 AM UTC-5, upsid...@downunder.com wrote:

On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

What so special about this ? There are a lot ground loop heat pump
installation, in which a large ground loop is installed 1-2 m below
ground in the garden. While some people call this "geothermal" but it
is just seasonal storage. The ground is heated in the summer and that
heath energy is extracted in the winter. The snow cover in the winter
reduces the heat loss directly from the ground.

If the garden is too small and too much heat is extracted from the
ground, the ground temperature may fall below 0 C, in the spring
freezing the ground and nothing will grow in the garden during the
early summer. Some house owners dump air condition heat in the summer
into the ground loop, melting the garden soil and enabling plant
growth. If a solar thermal collector is added to the system, it can be
used to heat the house earlier in the spring and also earlier dump
some heat into the ground loop, making it possible to start the
growing season earlier.

With a larger garden loop, there is not even a risk for freezing the
ground towards the spring.

"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

That is insane. If dumped into the soil, it dry up the soil
completely. If some wells drilled into the ground water that would be
a very bad idea, since the heat would flow away and may be illegal if
ground water is used for drinking water in the area.

,

80 C does seem crazy, I wonder if it comes close in practice?
I would like to see some analysis, but storing energy as heat
looks inefficient to me... why not PV and run heat pumps from the
50 F/ 10 C ground temperature (water?) to heat in winter and cool in summer.
(You'd need batteries for the PV's.)

George H.

 

[Clifford Heath]

On 27/1/20 4:53 pm, upsidedown@downunder.com wrote:

On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:
"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

That is insane. If dumped into the soil, it dry up the soil
completely. If some wells drilled into the ground water that would be
a very bad idea, since the heat would flow away and may be illegal if
ground water is used for drinking water in the area.

It talks about heavy insulation. I can't imagine that dumping heat into
the ground would be very efficient (over the span of seasons) unless you
had very good insulation to keep the heat from flowing away.

CH

 

[Bill Sloman]

On Tuesday, January 28, 2020 at 4:32:03 AM UTC+11, Rick C wrote:

On Monday, January 27, 2020 at 7:12:06 AM UTC-5, Bill Sloman wrote:
On Monday, January 27, 2020 at 7:39:49 PM UTC+11, Rick C wrote:
On Monday, January 27, 2020 at 12:53:28 AM UTC-5, upsid...@downunder.com wrote:
On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

What so special about this ? There are a lot ground loop heat pump
installation, in which a large ground loop is installed 1-2 m below
ground in the garden. While some people call this "geothermal" but it
is just seasonal storage. The ground is heated in the summer and that
heath energy is extracted in the winter. The snow cover in the winter
reduces the heat loss directly from the ground.

I've never heard anyone say heat pump geothermal is intended to store energy in the ground. Rather it uses the ground as a heat sink which is at a better temperature than the air which improves the efficiency of the heat pump. If the ground temperature changes much it would defeat the advantages of the constant temperature heat sink.

I also don't think the few feet of earth on top would be adequate insulation for seasons.

If I remember rightly, the temperature 45cm below the surface lags the seasons by six months (or 180 degrees) which is exactly what you want.

Not really. It is an irrelevant statistic. The issue at hand is heat loss. The fact that the thermal losses in winter cause the temperature to turn around in mid winter is not the important aspect. Consider the amount of insulation that will cause that effect, then add more insulation and you have a better storage system even though the temperature peak is now a different time.


A few feet of earth would be a bit more than that ...

And a better insulator.

The point is that the earth is both a thermal mass and an insulator. The point about the six month thermal lag 45 cm below the surface references both aspects, even if you haven't noticed this.

<snip>

Finland is a chilly place.

Non sequitur. Now you sound like JL.

Upside@downunder lives in Finland, which I happen to know, even if you don't.

You would have had to read a few of the posts with that header to notice, which I've done, even if you haven't.

--
Bill Sloman, Sydney

 

[Rick C]

On Monday, January 27, 2020 at 3:42:53 PM UTC-5, George Herold wrote:

On Monday, January 27, 2020 at 12:53:28 AM UTC-5, upsid...@downunder.com wrote:
On Sun, 26 Jan 2020 17:33:08 -0800, Jamie M <jmorken@shaw.ca> wrote:

Hi,

Here is an interesting geothermal project:

http://www.dlsc.ca/how.htm

In the summer solar thermal collectors are used to heat the ground, and
in the winter the heat is extracted from the ground:

What so special about this ? There are a lot ground loop heat pump
installation, in which a large ground loop is installed 1-2 m below
ground in the garden. While some people call this "geothermal" but it
is just seasonal storage. The ground is heated in the summer and that
heath energy is extracted in the winter. The snow cover in the winter
reduces the heat loss directly from the ground.

If the garden is too small and too much heat is extracted from the
ground, the ground temperature may fall below 0 C, in the spring
freezing the ground and nothing will grow in the garden during the
early summer. Some house owners dump air condition heat in the summer
into the ground loop, melting the garden soil and enabling plant
growth. If a solar thermal collector is added to the system, it can be
used to heat the house earlier in the spring and also earlier dump
some heat into the ground loop, making it possible to start the
growing season earlier.

With a larger garden loop, there is not even a risk for freezing the
ground towards the spring.

"The temperature of the earth will reach 80 degrees Celsius by the end
of each summer."

That is insane. If dumped into the soil, it dry up the soil
completely. If some wells drilled into the ground water that would be
a very bad idea, since the heat would flow away and may be illegal if
ground water is used for drinking water in the area.

,

80 C does seem crazy, I wonder if it comes close in practice?
I would like to see some analysis, but storing energy as heat
looks inefficient to me... why not PV and run heat pumps from the
50 F/ 10 C ground temperature (water?) to heat in winter and cool in summer.
(You'd need batteries for the PV's.)

George H.

What is inefficient about storing heat as heat??? Rather than convert to some other form of energy (electric, motion, elevated mass) which will have losses, heat seems perfect. Of course, that will have losses too, so it's a horse race as to which is better, meaning biggest bang for the buck, maintenance, reliability, etc.

From wiki,

Evacuated flat-plate solar collectors are a more recent innovation and can be used for Solar Heat for Industrial Cooling (SHIP) and Solar Air Conditioning (SAC), where temperature in excess of 100 °C (212 °F) are required.[4][5] These non-concentrating collectors harvest both diffuse and direct light and can make use of steam instead of water as fluid.

The system described does not use evacuated collectors I believe, but still I don't see any inherent limitation to get the working medium up to 80 °C.

--

Rick C.

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