Cromer cycle
This cooler, moister air can then be presented to the same cold surface as above to take it below its dew point and dry it further, or it can be expunged from the system.The desiccant undergoes a reversible process whereby in the first part of the cycle, it absorbs or adsorbs moisture from air leaving a cold surface, releasing heat, and then in the second part of the cycle evaporates moisture, absorbing heat and returning the desiccant to its original state to complete the cycle again.
This is shown in Figure 1 where a desiccant wheel has been applied to a standard air conditioning set-up.The psychrometric process of the air passing through the system with four state points is shown on the psychrometric chart of Figure 2 as 1, 2, 3 and 4.
Typical cooling and drying by the cold coil without the Cromer cycle is depicted on the psychrometric chart and is also shown in Figure 2.
State point 4' represents the temperature and moisture content of the air that leaves the typical unit, about 45–50 °F (7–10 °C) and 95–98% RH.
First, the end state point 4 for air from the wheel represents a latent ratio increase (moisture removal) to about 45%, as opposed to the 25% of the typical coil shown.
This is significant because, given a constant condenser temperature and equivalent change in enthalpy, the higher the evaporator coil temperature, the more efficient is the Carnot refrigeration cycle and the greater the energy efficiency a particular system can deliver.
These various strategies were compared in an ASHRAE Journal article that found that "the Cromer cycle produces similar enhanced dehumidification performance as is obtained with recuperative configurations.
Desiccants of Type III have plenty of potential for the cycling of moisture from the air off of the coil, around 98% RH, over to the return air stream, typically around 50% RH.In 2011, Khalifa, Al-Omran, and Mohammed reported on a monitored study of a 2-ton capacity air conditioner unit while exchanging out a silica gel wheel and a wheel made of activated carbon to determine if it would reduce the relative humidity in a small room in Baghdad when compared to the unit without the Cromer cycle added.
They found that the "Cromer cycle can reduce the indoor relative humidity from 80% to about 60% using active carbon of 5 cm wheel thickness.
Location 2 (but before the fan) is also the ideal place to bring outdoor air into the system, as the coil can then reduce its temperature and moisture before it enters the space.
Hot gas bypass heat can also be added to the process at location 4, called reheat, which delivers warmer but even lower RH supply air.
