riscy
Geotechnical
- Jul 22, 2007
- 22
I have been doing some research about the expansion tank sizing, antifreeze and so on. I experimented expansion equation from the ASHRAE and product data from various anti-freeze datasheets.
Vt = Vs((V2/V1)-1) - 3 ? ?t) / (1-(p1/p2))
ASHRAE demonstrated equation that account for both expansion coeff due to water *and* due to vessel tank (mostly steel). I found it is necessary to have expansion tank for HVAC and DHW within the building.
The expansion coeff for steel tank is 11.7mm/m.K
==================================================GSHP
I now looking into ground loop circuit where GSHP is connected. I need to work out how big the expansion tank needed for the project.
I knew brine expands 3-4 time faster than water (20% Ethylene Gycol + 80% water), this would lead to bigger expansion tank and thus an increase cost and installation space issue.
I worked out the expansion coeff of PE100 which is 0.150 mm/m.K (linear), this is many time faster than steel tank.
I don't know what is the linear expansion of the water, most of them are volumetric (~250e-6). Any suggestion?
Based on guideline document from website (non ASHRAE), popular equation occurs mostly for solar project:- Vt =Vv(B / (1-p1/p2), where B is expansion factor.
One source suggested B=0.13/K, but that apply to solar, not for GSHP.
I have acquired the volumetric coeff of the Ethylene Gycol from ASHRAE table (Fundamental Chap 22) based on 20% mix with 80% water.
-5 0.000 964 m/mK I used V=1/density conversion.
35 0.000 977 m/mk
With ASHRAE equation, I then calculated with PE100 pipe, and discovered that the PE100 expansion is actually faster than brine(!). Based on this, it seem to suggest that drop of pressure as you increase the water temperature (during cooling HVAC operation).
This calculation suggest I'm wasting the money with expansion tank as it does not do much. The PE100 is doing the works for you.
In addition, the water within pipe, tank, valve as part of HVAC system expands as well as expansion tank, this make sizing less critual.
On further thought, if you use plastic pipe within the DHW or heating network, it seem they expands faster than water and copper pipes, hence you may not need expansion tank.
Am i missing something, it too good to be true....
Comment welcome...
Vt = Vs((V2/V1)-1) - 3 ? ?t) / (1-(p1/p2))
ASHRAE demonstrated equation that account for both expansion coeff due to water *and* due to vessel tank (mostly steel). I found it is necessary to have expansion tank for HVAC and DHW within the building.
The expansion coeff for steel tank is 11.7mm/m.K
==================================================GSHP
I now looking into ground loop circuit where GSHP is connected. I need to work out how big the expansion tank needed for the project.
I knew brine expands 3-4 time faster than water (20% Ethylene Gycol + 80% water), this would lead to bigger expansion tank and thus an increase cost and installation space issue.
I worked out the expansion coeff of PE100 which is 0.150 mm/m.K (linear), this is many time faster than steel tank.
I don't know what is the linear expansion of the water, most of them are volumetric (~250e-6). Any suggestion?
Based on guideline document from website (non ASHRAE), popular equation occurs mostly for solar project:- Vt =Vv(B / (1-p1/p2), where B is expansion factor.
One source suggested B=0.13/K, but that apply to solar, not for GSHP.
I have acquired the volumetric coeff of the Ethylene Gycol from ASHRAE table (Fundamental Chap 22) based on 20% mix with 80% water.
-5 0.000 964 m/mK I used V=1/density conversion.
35 0.000 977 m/mk
With ASHRAE equation, I then calculated with PE100 pipe, and discovered that the PE100 expansion is actually faster than brine(!). Based on this, it seem to suggest that drop of pressure as you increase the water temperature (during cooling HVAC operation).
This calculation suggest I'm wasting the money with expansion tank as it does not do much. The PE100 is doing the works for you.
In addition, the water within pipe, tank, valve as part of HVAC system expands as well as expansion tank, this make sizing less critual.
On further thought, if you use plastic pipe within the DHW or heating network, it seem they expands faster than water and copper pipes, hence you may not need expansion tank.
Am i missing something, it too good to be true....
Comment welcome...