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Replace Electric Unit Heaters with Gas-Fired Equivalent |
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rev. 2008-11-25
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Replace Electric Unit Heaters with Gas-Fired Equivalent |
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rev. 2008-11-25
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Existing Conditions
Two electric unit heaters supply heat to the compressor room of this facility. Electric heating is a very expensive space heating method.
Retrofit Conditions
It is recommended that the two electric unit heaters be replaced with high efficiency Lennox sealed combustion unit heaters. These unit heaters have thermal efficiencies up to 81%. These units also operate only during the heating cycle (Energy Saving Ignition Control) and have an induced draft blower providing maximum efficiency and performance.
It is also recommended that the temperature of the space be reset to 10°C using electronic setback thermostats, during unoccupied periods.
Further Benefits
If the building has a demand meter, the peak load will decrease proportionately to the removed electrical load.
Application Details
Issues and Concerns
Natural gas may not be readily available to the space. If so, solar domestic hot water preheating may be an economical alternative to extensive piping construction.
References
Analysis
Electricity:
Heating value |
MJ/kg |
3,600.0 |
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Btu/lb |
1,547,721 |
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Fuel rate |
$/MWh |
100.00 |
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$/kWh |
0.100 |
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$/MWh |
100.00 |
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$/GJ |
27.78 |
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$/mmBtu |
29.31 |
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$/therm |
2.93 |
Natural Gas:
Heating value |
MJ/kg |
52.8 |
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Btu/lb |
22,700 |
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Fuel rate |
$/m³ |
0.40 |
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$/kWh |
0.038 |
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$/MWh |
38.41 |
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$/GJ |
10.67 |
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$/mmBtu |
11.26 |
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$/therm |
1.13 |
Case Example:
An electric water heater that produces 17000 gallons of hot water per day, which is enough for 30-50 people. It uses 1211.8 Mwh (4137.1 mmbtu) each year, or spends $121,180 each year. The total cost to retrofit the system to natural gas is $100,000, and the cost to heat the equivalent volume of water with natural gas at 80% efficiency is $55,854, which saves $65,326/year, and has a simple pay back of 1.5 years.