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Green Building Discussion
Topic: Humidity From Interior Plants
Discussion Participants:
- Bruce Coldham asks about plant transpiration rates
- John Halley suggests RMI for info
- Alex Wilson Does some calculations
- Marianne Buttner adds some sources of water
All postings are the opinion of the writer, and BuildingGreen can take no responsibility for their accuracy or appropriateness.
Bruce Coldham asks about plant transpiration rates
From: Bruce Coldham
Sent: Tuesday, November 05, 1996 4:11 PM
Can anyone help us find data on plant transpiration rates?
ARC Design Group is working on a project which involves a fair amount of interior plantings to create an indoor-outdoor feel for an office in Londonderry NH. The office will be well daylit - generally in excess of 100 footcandles where the plants will be. We are concerned that plants could add significant moisture to the space, or at least add some, which ought to be considered as part of the space conditioning load. But the question is how much, and to what extent is transpiration species/genus dependent?
We understand that moisture can derive from evaporation from the planter bed soil surface, and that that source is significantly removed by using sub-surface irrigation. However, even the horticulturalists and other plant people that we have so far been speaking with cannot provide us with real data - or even direct us to real data sources - on this subject.
Bruce Coldham ARC Design Group
John Halley suggests RMI for info
From: John Halley
Sent: Tuesday, November 05, 1996 11:57 AM
Bruce,
You might want to contact the Rocky Mountain Institute in Colorado about this. They may be a good resource for information on the effects of plant transpiration in buildings. Their offices are in a passive solar building with an extensive indoor garden. And I suspect that some of their staff may offer expertise in this area.
The Agriculture and Landscape Architecture Departments at the Davis campus of the University of California may also good resources. UC resources are easily accessed on the Internet.
If you care to, please post any interesting information you find on this topic.
Good luck,
John Edmund Halley C O M E T S T U D I O S P.O. Box 337, The Sea Ranch, California,
95497 USA Telephone voice & fax: 707-785-2567 E-mail: comet@cometstudios.com
Visit our web site: http://www.cometstudios.com
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Alex Wilson Does some calculations
From: Alex Wilson
Sent: Wednesday, November 06, 1996 4:15 AM
Bruce Coldham inquired about transpiration rates of plants. While I don't have exact answers on this question, I have some comments:
You could figure out roughly how much water vapor would be introduced into the indoor air by measuring how much water is used in watering the plants. As Bruce noted, the evaporated water in the air comes from two sources: evaporation from the planter bed, and from evapotranspiration of the plants.
Evaporation from the planter will depend on a) humidity of the space; b) how wet the soil is kept; and c) soil characteristics. There are tremendous differences in evaporation rates from different types of soil, as anyone from the old Soil Conservation Service will tell you (SCS has been renamed, but the new name escapes me).
Transpiration from the plants isquite different. During photosynthesis, for every two molecules of water consumed, one molecule of water is released (this is actually "new" water that has comes from the photosynthetic equation: CO2 + 2H2O + light = 02 + (CH2O - representing sugar) + H2O--sorry about the lack of subscripts).
Thus, if there were NO evaportion of water from the planter and all the added water was used by the plants, half as much water would be released as was added, the rest being converted into organic matter. My guess is that with most soils, indoor atmospheric conditions, and watering practices, considerably MORE water is introduced into the air by evaporation from the planting beds than from photosynthesis (transpiration). If that is the case, then measuring how much water is added to the plants would provide a pretty good estimate (high by perhaps 10-25%) of how much water vapor gets into the air.
I suspect you could get pretty good information on how much water is needed for commercial greenhouse management from somewhere. Try your local ag. extension agent.
Alex Wilson Environmental Building News
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Marianne Buttner adds some sources of water
From: Marianne Buttner
Sent: Wednesday, November 06, 1996 12:45 PM
Alex, In addition to the two sources of evaporated water in the air you mentioned in your reply to Bruce, there are lots more sources.
human and animal bodies showers/baths sinks toilet bowl evaporation pet water dishes
Marianne
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