FRIGOVENT air curtains for cold store doors and freezer rooms
THERMOVENT air curtains for service doors and factory gates

How much are the costs of the air exchange when opening a freezer room door?

The problem
Much of the current cost of a freezer room is caused by cold air loss through open doors.
There are also additional costs incurred due to icing of the freezing rooms, building damage and hoar frost as well as illegal changes in temperature of the goods.

Cold room air curtain

 

How much cold air is lost per second?
It‘s all about the cost of a door opening in EURO. This will determine how much cold air is lost at the door and how much warm air enters.

Cold air is 20% heavier than warm air and therefore it flows rapidly down out of the door opening. Through the upper part of the opening penetrates the same amount of warm air. The velocity of air movement is 1 m / sec.

Through an open freeezer room door with the opening size of 200 x 250 cm per second 2.5m³ cold air is lost.
The same amount of warm air streames into the room and must be cooled.

At an open standing time of 40 seconds 100m³ cold air is lost. 120m³ warm air has to be cooled in order to replace the lost cold air. During cooling, the air contracts and is 20% heavier - therefore you will need more warm air than you have lost as cold air.

How expensive is it to cool warm air from
+20°C down to - 20°C ?

For the cooling of 1m³ air from +20° C to - 20°C 100 kJ must be removed.
100 KJ correspond to 0.028 KW/h or 24 kcal.

 

Cold room air curtain

In order to produce 100m³ cold air, 120m² warm air must be cooled. Each m³ takes 0,028 KW/h 120 x 0.028 = 3.36 kW /h.

Save costs through the use of an air curtain of FRIGOVENT.

Cold room air curtains

 

For this, a chiller cooling unit also requires about 2,5 kW/h. At electricity costs of 20 cents per KW/h the energy costs for one door-opening come up to at least 0,50 EURO. Additionally there are the costs for repairs and depreciation.

A door opening with a cold air loss of 100m³ cost at least 50 cents. Daily at 30 openings it costs 15 EURO, 300 EURO per month, 3600 EURO annually. By using air curtains you can save 80 to 90% of these costs.

You can also make a test and collect the resulting condensation of the evaporator in a container.
Per cubic meter of warm air, which replaces the lost cold air , it must be cooled down and replaced, resulting 25 grams of condensation. So you have lost 400 cubic meters of cold air per 10 Liter bucket condensating water.

For more than one bucket a day at the evaporator condensation water of your freezer room is obtained, you should think about buying an air curtain system.

Fundamentals of cost calculation of the energy costs
due to air exchange when opening a cooling or freezer door.

Cold air has a higher weight than warm air:

Air temperature   The weight per cubic meter of air
- 20°C   1,39 kg
    0°C   1,27 kg
+20°C   1,18 kg

Cold air is 20% heavier than warm air. So it flows out when the door is open.
   

Cold air flows at a rate of 1m per second to the outside. Warm air enters respectively into the freezer.
At a refrigeration room door with the Opening size of 2 x 2.5 m are 2.5 m³ per second cold air is lost.
In 40 seconds there is a cold air loss of 100m ³.
The same amount of hot air flows into the freezer and is cooled down. The humidity is condensed and frozen on the evaporator. The condensate-ice is defrosted.

Cooling of hot air (100 cubic meters of + 20 ° C to - 20 ° C)   1.800 Kcal
Condensation of humidity (100 m³ air = 1 liter of water)   538 Kcal
Cooling from one liter of condensate water to 0 ° C   100 Kcal
Changing the physical state of the condensed water into ice   80 Kcal
Cooling of condensate ice at -20 ° C for   10 Kcal
When defrosting heating 1 liter of condensate ice at 0 ° C   10 Kcal
When defrosting conversion of condensate in ice water   80 Kcal
When defrosting heating of the condensate at 20 ° C   20 Kcal
     
Energy input for a door opening   2.638 Kcal
     
This will require the chiller electricity of 2.5 KW a € 0.20 0,50
Daily costs of 30 door openings per day 15,00
Monthly charges for 20 working days 300,00
Cost savings through use of an air curtain per year 3.600,00

The cost of the cold air loss at cold room doors are half as high, because cold air is not as cold as air of freezing rooms. On the other hand, cold room doors are open longer and operates more often. A calculation shows similar results here in refrigeration room door.

80-90% of these costs for cold air leaks can be saved by air curtains.