Question for other greenies/hippies/nerds on this site.
I'm working on the design of an electricity-free tiny structure in the California desert. Has anyone heard of an active solar hydronic design as follows?... It seems so elegant that I can only presume the reason I can't find any discussion of it is that it doesn't work:
An array of solar collectors which by thermosiphoning (no pumps) feed a water/glycol solution directly (no tank) to a closed loop hydronic radiant slab? Temperature control would only be afforded by a globe valve.
My guess is that collectors are unable to generate enough pressure by way of thermal expansion in the water/glycol to push the liquid and overcome pipe friction.
By way of background:
-Site conditions preclude passive solar techniques, and the requirement that the design no require electricity (PV or other) is a condition of both the location and personal preference.
-The location has significant solar potential in the winter months, but is also subject to freezing (hence the glycol solution).
-It's a very high thermal mass design and I am relying on daytime heating and thermal lag to provide acceptable temperatures (+17 degrees C at night)
I haven't seen anything like that.
It has been my experience that the heating loops undermine your high mass more than they help it (In our course for passive heating, you can't use the portion of the mass with the tubes in your mass calculation). Have you considered a high performance modified trombe wall, similar to this
It seems like a better fit for what you are describing. If you need help on sizing, I can send you more information.
Interesting thoughts, especially about the conflict between the hydronic system and the mass it is cast into. Do you know why that is? In this case, it would be an adobe structure with somewhere between 18"-24" walls, so the bulk of the mass would be outside the radiant floor slab.
I've thought a lot about the vented trombe walls (was looking at a 1979 NREL study on the Kelbaugh House earlier today), but unfortunately the site is very skinny and north-south oriented. The reason I was thinking of hydronic with solar collectors is that the allows for roof mounting that doesn't require such specific building geometry as more conventional passive designs.
Let's go back to step 1. Have you created a bioclimatic chart for the site? That's the first thing you should do. Use a nearby airport's data for average humidity and temperature. Email me if you're lost.
we've seen the system you've described done on a dnr project here, except... they were running an active pump. however, the radiant loop was being fed into a solar hot water heater. we've had the same system specified for several houses, but usually lose the hot water heater component.
the pressure you need to feed the radiant is indeed pretty steep - i've never considered it with a thermosiphoning option. sounds really intriguing, but if you can't get any active electricity (pv or otherwise) to generate the pump, i'm not sure you'd get enough pressure (a lot depends on the loop configuration and length though - if this is for a 300sf room, that's one thing. if it's for a 1500sf house, that's another).
keep us informed - i'm a huge fan of the combo we're using. all you pay for heat in the winter is the electricity to run the pump...
For the summer cooling season, it's got all of the characteristics that lead one to high thermal mass/night cooling: low humidity and large diurnal temperature swings.
For winter, the average minimum temperatures is 35 degrees F. The winter heating design temperature is 25 degrees F.
What are some of the books that you guys are looking at for this kind of stuff?
Also, are you using any particular software for mass calcs, solar gains / losses, etc?
I'm having a tough time getting much info out of our consultant pool... they've done a lot of LEED projects, but they seem fairly ignorant of most of this lower-tech hippie stuff.
I have some recommended books listed here.
Mechanical and electrical equipment for buildings is a great source for the in-detail calculations required for this lower tech stuff. Sun wind and Light have a great analysis approach for finding what will work best for you.
I have a tutorial for doing a bio-climactic chart here.
janosh-
I will see if I can dig out the papers from my time with John Reynolds and GZ Brown up in Oregon to see if there was a specific reason for the exclusions. I don't remember the why, just that John was adamant that the area couldn't be used for high mass.
for those folks reading this thread and wondering how to create a bioclimatic/psychrometric chart - there is a range of free software that will do it for you.
My favorite is Climate Consultant 3.0 developed at UCLA. it uses energy plus's weather files which are available for most locations around the world. I've had great luck contacting folks at the eere and the energyplus yahoo group for locations that aren't listed (like Baku, Azerbaijan).
janosh- you're heading in the right direction with the thermal mass design. Don't forget to consider the roof as part of the thermal mass.
do you guys know how much heat loss occurs in the passive systems at night? I assume that their is still liquid flowing through the collectors when the sun aint out; which could lead to a heat loss????
at night, there isn't a convective thermo siphon effect. but there can be a solinoid valve installed to stop heat loss/flow when the temp diffis big enough. Also drainback systems are popular - they often use a pv cell to power a pump - very simple feedback loop - more sun, more pumping.
Jan 13, 09 9:09 pm ·
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Active Solar Hydronic Heating
Question for other greenies/hippies/nerds on this site.
I'm working on the design of an electricity-free tiny structure in the California desert. Has anyone heard of an active solar hydronic design as follows?... It seems so elegant that I can only presume the reason I can't find any discussion of it is that it doesn't work:
An array of solar collectors which by thermosiphoning (no pumps) feed a water/glycol solution directly (no tank) to a closed loop hydronic radiant slab? Temperature control would only be afforded by a globe valve.
My guess is that collectors are unable to generate enough pressure by way of thermal expansion in the water/glycol to push the liquid and overcome pipe friction.
By way of background:
-Site conditions preclude passive solar techniques, and the requirement that the design no require electricity (PV or other) is a condition of both the location and personal preference.
-The location has significant solar potential in the winter months, but is also subject to freezing (hence the glycol solution).
-It's a very high thermal mass design and I am relying on daytime heating and thermal lag to provide acceptable temperatures (+17 degrees C at night)
I haven't seen anything like that.
It has been my experience that the heating loops undermine your high mass more than they help it (In our course for passive heating, you can't use the portion of the mass with the tubes in your mass calculation). Have you considered a high performance modified trombe wall, similar to this
It seems like a better fit for what you are describing. If you need help on sizing, I can send you more information.
Hey Joshcookie...
Interesting thoughts, especially about the conflict between the hydronic system and the mass it is cast into. Do you know why that is? In this case, it would be an adobe structure with somewhere between 18"-24" walls, so the bulk of the mass would be outside the radiant floor slab.
I've thought a lot about the vented trombe walls (was looking at a 1979 NREL study on the Kelbaugh House earlier today), but unfortunately the site is very skinny and north-south oriented. The reason I was thinking of hydronic with solar collectors is that the allows for roof mounting that doesn't require such specific building geometry as more conventional passive designs.
Janosh,
Let's go back to step 1. Have you created a bioclimatic chart for the site? That's the first thing you should do. Use a nearby airport's data for average humidity and temperature. Email me if you're lost.
Cheers!
Make: did that first!
Excellent!
What did you come up with?
janosh -
we've seen the system you've described done on a dnr project here, except... they were running an active pump. however, the radiant loop was being fed into a solar hot water heater. we've had the same system specified for several houses, but usually lose the hot water heater component.
the pressure you need to feed the radiant is indeed pretty steep - i've never considered it with a thermosiphoning option. sounds really intriguing, but if you can't get any active electricity (pv or otherwise) to generate the pump, i'm not sure you'd get enough pressure (a lot depends on the loop configuration and length though - if this is for a 300sf room, that's one thing. if it's for a 1500sf house, that's another).
keep us informed - i'm a huge fan of the combo we're using. all you pay for heat in the winter is the electricity to run the pump...
Make:
For the summer cooling season, it's got all of the characteristics that lead one to high thermal mass/night cooling: low humidity and large diurnal temperature swings.
For winter, the average minimum temperatures is 35 degrees F. The winter heating design temperature is 25 degrees F.
What are some of the books that you guys are looking at for this kind of stuff?
Also, are you using any particular software for mass calcs, solar gains / losses, etc?
I'm having a tough time getting much info out of our consultant pool... they've done a lot of LEED projects, but they seem fairly ignorant of most of this lower-tech hippie stuff.
Kurt
I have some recommended books listed here.
Mechanical and electrical equipment for buildings is a great source for the in-detail calculations required for this lower tech stuff. Sun wind and Light have a great analysis approach for finding what will work best for you.
I have a tutorial for doing a bio-climactic chart here.
janosh-
I will see if I can dig out the papers from my time with John Reynolds and GZ Brown up in Oregon to see if there was a specific reason for the exclusions. I don't remember the why, just that John was adamant that the area couldn't be used for high mass.
j
for those folks reading this thread and wondering how to create a bioclimatic/psychrometric chart - there is a range of free software that will do it for you.
My favorite is Climate Consultant 3.0 developed at UCLA. it uses energy plus's weather files which are available for most locations around the world. I've had great luck contacting folks at the eere and the energyplus yahoo group for locations that aren't listed (like Baku, Azerbaijan).
janosh- you're heading in the right direction with the thermal mass design. Don't forget to consider the roof as part of the thermal mass.
do you guys know how much heat loss occurs in the passive systems at night? I assume that their is still liquid flowing through the collectors when the sun aint out; which could lead to a heat loss????
mdler,
at night, there isn't a convective thermo siphon effect. but there can be a solinoid valve installed to stop heat loss/flow when the temp diffis big enough. Also drainback systems are popular - they often use a pv cell to power a pump - very simple feedback loop - more sun, more pumping.
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