Dehumidification >> What Is A Normal Dehumidifier Setting In Degrees

Recuperative heat exchange is a universal technology applicable to vapor-compression, direct-expansion, and chilled-water air-handling-unit (AHU) coils; heat-powered desiccant dehumidification equipment; dehumidifiers; supermarket, ice-rink, and natatorium air-conditioning and dehumidification systems; and packaged 100-percent-outside-air conditioners. This installment discusses five types of What Is A Normal Dehumidifier Setting In Degrees recuperative sensible-heat exchangers that are used to prevent over cooling while still meeting the dehumidification needs of a conditioned space.
 
 The energy aspects of this technology are explained in great What Is A Normal Dehumidifier Setting In Degrees detail. The reason for this is that many owners and designers are under the incorrect assumption that there are no penalties associated with the use of hot-gas or condenser-water reheat. This is not to say that one should always use some form of recuperative heat exchange in preference to hot-gas or condenser water reheat.
 
It simply is to say that owners and designers should be aware that there is a more energy-efficient way to accomplish reheat while also What Is A Normal Dehumidifier Setting In Degrees reducing the required cooling capacity. Also addressed in this installment are the four penalties associated with ordinary "new-energy” reheat and a technology that is used to avoid one of those penalties: reheat using hot refrigerant gas.
 
RECUPERATIVE DEHUMIDIFICATION
 Recuperative-dehumidification enhancements are good solutions for 100-percent-outside-air cooling units. Five such enhancements are: 1) Coil-loop run-around precooling and What Is A Normal Dehumidifier Setting In Degrees reheating coils (water or glycol). 2) Heat-pipe run-around precooling and reheating coils. 3) Air-to-air flat-plate heat exchangers for precooling and reheating. 4) Rotary-wheel heat exchangers for precooling and reheating. 5) Refrigerant liquid subcooling/airreheating coil.
 
Each of the first four enhancements involves one heat-transfer device located upstream from the main cooling coil and one heat-transfer device located downstream from the main cooling coil. The What Is A Normal Dehumidifier Setting In Degrees upstream device precools air as it enters the main cooling coil, while the downstream device reheats the air by the same enthalpy change as it leaves the main cooling coil. Other than a small increase in fan energy to overcome the added air friction of the precooling and reheating sections and a fractional-hp pump for the coil-loop enhancement, no external energy is used.
 
 (If the heattransfer devices are active for only a small portion of the annual operating hours, consider bypass dampers to reduce the annual energy impact.) The first four enhancements can be applied to any type of primary cooling coil: chilled water, chilled What Is A Normal Dehumidifier Setting In Degrees glycol, or refrigerant. If the primary coil is of the refrigerant type, then the performance of the refrigeration system must be verified at mild- and cool-weather entering-air conditions to ensure that the refrigeration system will operate without compressor cycling or liquid slugging and with proper oil return.
 
 Suction temperatures above 30 F are necessary to prevent frost or ice accumulation on the main cooling coil. The performance of 100-percentoutside-air recuperative-dehumidification What Is A Normal Dehumidifier Setting In Degrees enhancements varies from a maximum temperature change at peak cooling conditions to no temperature change at an outside temperature of approximately 50 F. This performance usually is acceptable because the latent load of the outside air declines with outside temperature.
 
Applications must be analyzed to determine if additional reheat (from hot refrigerant gas, electric heating coils, thermal heating coils, or in-space heat sources) is required to maintain acceptable space conditions. Supplementary reheat coils, if required, must be located What Is A Normal Dehumidifier Setting In Degrees downstream from the recuperative-dehumidification reheat coil. Heating, recuperative-reheat, and conventional reheat coils must be separated from the main cooling coil to allow condensed moisture to drain from the main cooling coil without being re-evaporated by radiant or conducted heat.
 
 The main cooling coil must be selected at a coil face velocity at least 150 fpm below the maximum cataloged face velocity to ensure What Is A Normal Dehumidifier Setting In Degrees that moisture does not carry over onto a reheat coil (liquid water carryover onto an active reheat coil results in additional energy consumption and humidification). AHU fans and motors (if the motor is in the air stream) should be located downstream from the recuperative reheat system for optimum effectiveness.
 
If a supplementary reheat coil is used and its leaving-air temperature is above 100 F, then the fan motor must be selected for reliable operation at the actual temperature conditions at the motor. It may be necessary to de-rate the motor and use Class F or H high What Is A Normal Dehumidifier Setting In Degrees temperature motor-winding insulation. Special motors are not required for recuperative-reheat systems not equipped with supplementary reheat coils. Because of the possibility of moisture condensing on precooling heat-transfer surfaces during part-load operating conditions, provisions for collecting and draining condensate must be made.
 
 Heat-exchange surfaces will accumulate particulate even with well maintained filters. Surfaces should be accessible and cleanable without difficulty or high cost. The fifth recuperative-dehumidification enhancement is superior to the other four in many respects because it achieves almost the same result with a single coil located What Is A Normal Dehumidifier Setting In Degrees downstream from the main cooling coil. The single coil reduces first cost, halves the air-side friction of the recuperative elements, and requires no space or modifications upstream from the main cooling coil.
 
With the fifth enhancement, which is applicable only to systems using refrigerant coils served by compressors, the amount of What Is A Normal Dehumidifier Setting In Degrees reheat is limited. If a significant temperature rise is required, this enhancement may need to be combined with one of the other four. Details on each of the five recuperative-dehumidification enhancements follow.
 
 COIL-LOOP RUN-AROUND PRECOOLING, REHEATING
Run-around coils for enhanced dehumidification systems are not a new technology. They are well-described in texts from as long ago as 1939.1, 2, 3, 4 The psychrometric-chart analysis of run-around coils for precooling and reheating is identical to that for What Is A Normal Dehumidifier Setting In Degrees ordinary reheat (see sidebar) with one exception: The precooling coil cools the entering air from 84- to 72-F dry bulb (DB); therefore, the air entering the main cooling coil is cooler, which means that the main cooling coil does not have to remove as much heat.
 
The reheat is provided not by an external source of expensive energy, but by the heat picked up by the circulating fluid in the precoil. The cycle and savings are illustrated in Figure 2. Figure 3 is a What Is A Normal Dehumidifier Setting In Degrees piping diagram showing that run-around coils require a small closed-loop piping system. When freezing is a possibility, the heat-transfer fluid is dilute ethylene glycol; at other times, it is water.

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