Frosting in air-to-air energy exchangers is a commonproblem when the outdoor air temperature is very low.Membrane-based air-to-air energy exchangers that arecapable of moisture transfer as well as sensible heat transfermay assist in overcoming frosting. To understand the effect ofwater vapor transfer on frosting, laboratory experimentswere conducted to investigate the frosting conditions for twogeometrically identical air-to-air cross-flow plate exchangers.One exchanger was made with a water vapor permeablemembrane (energy exchanger), while the other exchangerwas made with an impermeable polymer film with similarthickness (heat exchanger). Tests for heat and energyexchangers were conducted in several operating conditionsto detect the conditions that resulted in frosting in theexchangers. The laboratory test conditions for the exchangerswere 0°C (32°F) to -32°C (-26°F) for the supply inlet(simulated outdoor air) temperature and 5% to 55% exhaustinlet (simulated indoor air) relative humidity, while exhaustinlet temperature was about 22°C (72°F). Flow rates in the supplyand exhaust air streams were maintained at 20.8 L/S(about 40 cfm) to provide a balanced mass flow rate of dry airbetween the two air streams. Experimental results confirmedthat the energy exchanger was more frost resistant than theheat exchanger. For example, when the indoor relativehumidity was 30%, frost formed in the energy exchanger foroutdoor temperatures of -10°C (14°F) or lower, whereas theheat exchanger frosted at -5°C (23°F). Additionally, thelower the indoor relative humidity, the lower the frosting limittemperature. Both heat and energy exchangers experiencedfrosting for almost all indoor relative humidities tested whenthe supply temperature was less than -25°C (- 13°F). Determiningthe operating conditions in which frost first begins toform (frosting limit) will help designers and engineers toselect a suitable exchanger and apply proper frost protectiontechniques.
Citation: 2017 Winter Conference, Las Vegas, NV, Transactions, Vol 123, Pt 1
Product Details
- Published:
- 2017
- Number of Pages:
- 8
- Units of Measure:
- Dual
- File Size:
- 1 file , 2.6 MB
- Product Code(s):
- D-LV-17-016
