I have done the calculations on the viability of heat recovery in mushroom cultivation several times and could never persuade myself that they were worth fitting.

Even when calculations were done with fossil fuels as the energy source they were not viable, and with the switch to biomass fuels then it is not possible to even break even.
The Dutch fitted them years ago and I don’t know of any that are still in use. The Dutch also  have higher extremes of weather conditions than we have.
 
1 Kwh will heat 3,000 m3/hr by 1C (assuming no condensation).
The ideal temperature for air entering a growing room is below 14 C. Above that it will increase the cooling load.
 
A 50 tonne house will require a maximum of 5,000 m3/hr of fresh air.
During the cropping I assume it will use an average 3,000 m3/hr.
Fresh air is required 66% of the time.
 
Taking mean temperatures average over the past 30 years.
 
MONTH    MEAN TEMP    POTENTIAL INCREASE
 
JAN                 5                        +9
FEB                 6                        +8
MARCH          7                        +7
APRIL             8                        +6
MAY               12                      +2
JUNE              14                      +0
JULY               15                      +0
AUG               15                      +0
SEPT              13                      +1
OCT               10                      +4
NOV                7                      +7
DEC                 5                      +8
 
The average potential temperature gain is 4.5C
If the outside temperature is over 20C you will gain some cooling benefit but this will be cancelled by negative effect when outside is between 14C and 18C.
When using cold outside air to cool compost you will get a negative effect as the air will be heated coming in. This is perhaps the biggest negative of heat recovery.
Assuming the above all cancels out then our savings on heat is:
 
4.5 kw x 365 x 24 x 0.66 = 26,000 kw
Heat from pellets cost 5 cent /kw.
Saving €1,300  per annum.
<b>
Running costs:</b>
2 fans @ 1 kw = 2 kw x 365 x 24 x 0.66 = 11,500 kw
11,600 kw @ 0.18 = €2,000 extra cost.
The fans will not run at full speed all of the time, but you will not get full heat recovery to balance this.

Then we have filters, labour to wash system, disease risk, higher cooling costs and the costs to maintain system: not forgetting the cost of investment.

OK they are fantastic when it is –10C or + 30C outside but we seldom get these conditions.
 
I am convinced heat recovery will not give any saving and could cost you an extra €1,000 to €1,500 per tunnel per annum?

I have no hidden agenda here. I am an equipment supplier and actually had a system designed but decided not to launch it unto the market.
 
by David Totten