Room Temperature Guide for Compressed Air Systems
Compressed air systems often have to perform in an environment that is not ideal for their operation. Two conditions that are averse to efficiently making compressed air are high humidity and extreme room temperature. Damp conditions, notably wet sub-floors, require more work and maintenance of the dryer system and contribute to a greater number of needed air releases from condensate drains. High room temperatures also require more work from the compressor system, including greater wear on motor bearings and other more frequent maintenance items.
Compressing cool air is more practical than compressing warm air as it is denser, making it easier to compress. Warmer air, especially during the summer months or in a shop mezzanine, is more difficult to compress and poses an increased load on the system. To utilize cooler air in a compressed air system, supply vents from a cooler location should furnish air to the area surrounding the compressors. The supply vents can be from cooler areas inside the facility or directly vented from the outside. Furthermore, removing heat from a compressor is another tool to reduce the temperature of the compressor room. By recovering the heat through an exchanger to heat building air, preheat combustion air, or heat oil or water, a compressor is not contributing additional heat that would make it less efficient.
When designing the ventilation system, a louver should be installed to close the ventilation if the outside air temperature exceeds the building temperature or if the outside air is too cold, which can cause condensation of water in lubricant-injected systems.
To determine the payback of redesigning the compressor room ventilation, use the table below to figure the amount of savings associated with reducing the operating temperature of the room. As a rule of thumb above the freezing temperature, every 10°F reduction in the compressor intake air temperature doubles the amount of energy savings.
For example, reducing the temperature of the compressor room 10°F with two 50-hp motors will save approximately $132 annually. (Assumes operation is 2080 hr/yr at an electrical cost of $0.05/kWh.)
| Change in Inlet Temperature | -5°F | -5°F | -10°F | -10°F | -20°F | -20°F | -30°F | -30°F | -40°F | -40°F |
|---|---|---|---|---|---|---|---|---|---|---|
| Compressor Size | Energy Savings (kWh) | Annual Savings | Energy Savings (kWh) | Annual Savings | Energy Savings (kWh) | Annual Savings | Energy Savings (kWh) | Annual Savings | Energy Savings (kWh) | Annual Savings |
| 5 hp | 66 | $3 | 132 | $7 | 263 | $13 | 395 | $20 | 527 | $26 |
| 10 hp | 132 | $7 | 263 | $13 | 527 | $26 | 790 | $40 | 1054 | $53 |
| 15 hp | 198 | $10 | 395 | $20 | 790 | $40 | 1185 | $59 | 1580 | $79 |
| 20 hp | 263 | $13 | 527 | $26 | 1054 | $53 | 1580 | $79 | 2107 | $105 |
| 25 hp | 329 | $16 | 659 | $33 | 1317 | $66 | 1976 | $99 | 2634 | $132 |
| 30 hp | 395 | $20 | 790 | $40 | 1580 | $79 | 2371 | $119 | 3161 | $158 |
| 40 hp | 527 | $26 | 1054 | $53 | 2107 | $105 | 3161 | $158 | 4214 | $211 |
| 50 hp | 659 | $33 | 1317 | $66 | 2634 | $132 | 3951 | $198 | 5268 | $263 |
| 75 hp | 988 | $49 | 1976 | $99 | 3951 | $198 | 5927 | $296 | 7902 | $395 |
| 100 hp | 1317 | $66 | 2634 | $132 | 5268 | $263 | 7902 | $395 | 10536 | $527 |
| 200 hp | 1976 | $99 | 3951 | $198 | 7902 | $395 | 11853 | $593 | 15804 | $790 |
| 300 hp | 2634 | $132 | 5268 | $263 | 10536 | $527 | 15804 | $790 | 21072 | $1,054 |
| 400 hp | 3951 | $198 | 7902 | $395 | 15804 | $790 | 23706 | $1,185 | 31608 | $1,580 |
| 500 hp | 5268 | $263 | 10536 | $527 | 21072 | $1,054 | 31608 | $1,580 | 42144 | $2,107 |
Energy and cost savings associated with lowering the compressed air intake temperature from 5 to 40°F. Assumes 2,080 hrs/yr of operation at an electrical cost of $0.05/kWh, compressor running loaded 80% of the time (unloaded = 20%), and a 75% power reduction when the system is unloading