Subject: Heating in hot-houses

From: [email-masked] (Warren de Villiers)
Date: 1 Nov 1995 19:45:24 GMT

I would like to know how many watts it would take to raise the 
temperature of 1 cubic meter of air by 1 degree celcius. This is in
an insulated hot-house in New Zealand (North Island). I'm not sure I,m
in the right newsgroup for this, but any suggestions to solve my problem
are welcome. If any more information is neeeded, please e-mail me or write
to the newsgroup.

Thanks

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From: [email-masked] (Stavros Macrakis)
Date: 02 Nov 1995 15:17:51 GMT

In article <[email-masked]> [email-masked] (Warren de Villiers) writes:

   I would like to know how many watts it would take to raise the 
   temperature of 1 cubic meter of air by 1 degree celcius. This is in
   an insulated hot-house in New Zealand (North Island)....

The amount of _energy_ (watt-hours, joules, calories, therms)
necessary to raise the temperature of 1 m3 of air by 1 degree is
small, something like .2-.3 watt-hour/m3/degC, depending on humidity
etc.

But what you probably care about is how much _power_ (watts,
therms/day) is necessary to _maintain_ a given temperature.  This is
not a function of volume, but a function of heat gain and loss by
convection (air movement), conduction (heat transmission through
material), and radiation (heat transmission as electromagnetic waves,
e.g. light, infrared, etc.).

Convection and conduction losses are proportional to the heat
difference between the inside and the outside.  Convection is
proportional to the air leaks in your building, wind speed, etc.
Conduction is inversely proportional to the insulating capacity of
your outside surfaces, and proportional to their area.  Radiation is
proportional to the area of radiation-transmitting surfaces (such as
glass).

I would think any book on greenhouse engineering would discuss all
this in detail.

	-s