PE 013
Refrigerant based
dehumidification
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How do they work?
They’re just a decent size refrigeration unit
Evaporator
Warm,
wet air
20oC
85% RH
15g/m3 of water
Condenser
Cold air
Warm
dry air
16oC
100% RH
14g/m3 of water
30oC
45% RH
14g/m3 of water
Compressor
Water
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The energy balance
Evaporator
Warm,
wet air
Condenser
Cold,
wet air
Warm
dry air
4kWh
Compressor
Water
1kWh
3kWh
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Simple energy costs
Cost of
electricity
Cost of heat
(CoP of 4.0)
Equivalent cost of gas
(85% efficient boiler)
9 p/kWh
2.3 p/kWh
1.9p/kWh (56p/Therm)
6p/kWh
1.5p/kWh
1.3p/kWh (37p/Therm)
• But there’s more….
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A bit more physics
• What happens when the vents are
open?
– Lose the energy in the water vapour
(latent heat)
– Lose the energy in 20oC air that is
replaced with say 10oC air (specific heat)
– This adds 1 to the CoP
• New CoP is 5.0
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Cost of
electricity
Cost of heat
(CoP of 5.0)
Equivalent cost of gas
(85% efficient boiler)
9 p/kWh
1.8 p/kWh
1.5p/kWh (45p/Therm)
6p/kWh
1.2p/kWh
1.0p/kWh (30p/Therm)
The project at Red Roofs Nursery
• 4 dehumidifiers in 6,000m2
• Each unit
– Consumes 10kW electricity
– Removes 45 litres/hr of water
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Energy facts/figures
• 2013
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Energy facts/figures
• 2014
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Energy facts/figures
• Total heat use - 2013
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Energy facts/figures
• Total heat use - 2014
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Energy facts/figures
• Heat saved
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Energy facts/figures
• Electricity used
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Crop data
• 2013
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Control
Dehumidifier
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Crop data
• 2014
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Control
Dehumidifier
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Financials
• Check out the spreadsheet
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