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Old 02-01-13, 03:45 PM   #393
Fornax
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Quote:
Originally Posted by kostas View Post
6. Post heating exchanger (as n.3 but with more power, like 2Kw or so)
I think 2kW or so is too much.

Asuming 70 m^3/h and 80% efficiency and inside temperature of 20C, fresh air 0C you need to heat the air something like 4C (7F). (You intend to preheat the incoming air, I asume the lowest setting of fanspeed and low pressuredrop.)

70 m^3 of air is about 70 *1.2 = 84kg.
The specific heat of air is around 1,0 kJ/(kg*K) (ignoring moisture here)

Now to heat 1 hour worth of airexchange you need roughly:
84kg/h * 4K * 1,0kJ/(kg*K) = 336kJ/h.
This translates to 336000J/3600s = 93J/s or 0,1kW of heating capacity.

You are just heating up 20 liters per second of air a few degrees, not an entire room at once.

And indeed swapping #11 and #12 will fix it. You always want the two warm flows on one end and the two cold flows on the other end.
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