Heat pumps that increase the temperature of a low-grade waste heat stream that may otherwise be exhausted to the environment, to make it more useful for industry—for direct process use or to preheat supply or combustion air.
Industrial heat pumps convert low-grade waste heat that would otherwise be rejected into the environment into high grade thermal energy that is useful to industry. To boost the temperature of the low grade heat, mechanical heat pumps require shaft horsepower and consume electrical energy.
The coefficient of performance (COP) of a heat pump is equal to the useful energy output divided by the energy input. COP decreases as the temperature lift (difference between the evaporator and condenser temperatures) increases.
Continuous flow dehumidification heat pump dryers dehumidify process air with the evaporator coils of a refrigeration system, and then reheat supply air at the condenser coils. They save energy by continuously recycling heat and air within the dryer rather than discharging it to atmosphere. These units generally have a COP between 5 and 7 when used at low and moderate temperatures and are ideal for drying of lumber and food products. Energy requirements approach 300 Btu per pound of water vapor removed, about 1/10th of the energy required in conventional dryers. Designs must ensure that heat transfer surfaces are easily cleaned, to prevent fouling.
Heat pumps are useful when they can deliver heat at a lower cost than the next best alternative. Alternatives are usually natural gas, propane or other fuel-fired equipment such as steam systems or burners in an oven or dryer. Mechanical heat pumps use electrical energy while savings natural gas, biomass, or other fuels.
Status:
Baseline Description: Dryer with Dehumidification Heat Pump Baseline Energy Use: 51344272 kWh per year per Dryer
This analysis assumes installation of a dehumidification heat pump on an apple dryer that initially consumes 206,163 MMBtu/year of natural gas. Units are converted to electrical energy equivalents given an 85% burner efficiency as some dryers may not use direct fired gas heat due to taste and flavor issues associated with direct combustion product contact. The dehumidification heat pump would recover the heat of vaporization of water vapor in the exhaust stream and preheat the supply air to the dryer to 140 deg F. Annual energy savings (given 350 tons/day processed, 38 weeks/year, 51% run time per day, and moisture content reduction in the product from 80% to 20%) are 13,765,016 kWh/year, equivalent to 26.8% of the baseline energy use.
"Typical" Savings: 27% Energy Savings Reliability: 4 - Extensive Assessment
Energy Use of an Emerging Technology is based upon the following algorithm. Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
WSU EEP, 06/11/2009. Industrial Heat Pumps for Low-Temperature Heat Recovery Washington State University Extension Energy Program, Industrial Services
IEA/OECD, 01/01/2013. Heat Pumps in Industry IEA/OECD Heat Pump Centre
Cecilia Arzbaecher, 06/21/2007. Industrial Waste-Heat Recovery: Benefits and Recent Advancements in Technology and Applications European Council for an Energy Efficiency Economy
EERE, 07/15/2003. Industrial Heat Pumps for Steam and Fuel Savings Industrial Technologies Program