Dehumidification >> How To Choose A Professional Dehumidifier

Flat-plate heat exchangers consist of a series of flat How To Choose A Professional Dehumidifier or nearly flat heat exchange surfaces arranged in such a way that alternating air passages are connected to one air stream with remaining passages connected to the second air stream. the recuperative application of the air-to-air flat-plate heat exchanger. 

The precooling section should be sloped in the direction of air flow to a condensate drain. Advantages. The main advantages of flat-plate heat exchangers are: They have no moving parts. They have no external connection to water circuits, ethylene glycol, refrigerant, How To Choose A Professional Dehumidifier or electricity. They have no heat-transfer fluids that are subject to freezing. 

Disadvantages of flat-plate heat exchangers are: Control is impossible unless bypass How To Choose A Professional Dehumidifier dampers are used. The physical arrangement of their external components is more restrictive than that of the other recuperative-dehumidification enhancements because of the requirement of alternate air streams in cross-flow or counterflow arrangements. 

ARI-certified ratings are not available. Some leakage How To Choose A Professional Dehumidifier or cross flow may occur if the sealant at the edge of plates is not perfect. ROTARY-WHEEL HEAT EXCHANGERS The rotary-wheel heat exchanger usually consists of a honeycomb (fluted) aluminum rotor. An 8-in.- wide corrugated layer of aluminum sheet and an 8-in.-wide flat aluminum sheet are wound around a hub to create an 8-in.-deep rotor (depth varies by manufacturer) with diameters up to about 8 ft. 

The rotor usually is encased in a housing (cassette) that includes seals at the wheel periphery How To Choose A Professional Dehumidifier and at the sectional divider between air streams. The rotor housing is ducted to the two air streams as shown in Figure 7. Onehalf of the rotor picks up heat from the warm air stream. As the rotor rotates at about 20 rpm, this heat is transferred to the cool air stream. 

Advantages.The main advantages of rotary-wheel heat exchangers are: There is no water, How To Choose A Professional Dehumidifier ethylene glycol, or refrigerant charge. Control is easy. They have no heat-transfer fluids that are subject to freezing. Disadvantages. Disadvantages of rotary-wheel heat exchangers are: A restricted physical arrangement of inlet and outlet air streams. 

The requirement of 120-v, 60-cycle single-phase power to a fractional-hp motor. ARI-certified ratings are not available. The media in the rotor may be susceptible to clogging. Some drive systems How To Choose A Professional Dehumidifier have been unreliable or have required high maintenance. The life of the rotor may be shorter than that of other options. 

Leakage between air streams reduces effective air quality and performance. The initial leakage rate may be acceptable; however, How To Choose A Professional Dehumidifier the wearing of seals, etc. can result in increased leakage. Condensation may be detrimental to some types of rotors and media. REFRIGERANT LIQUID SUBCOOLING/AIR REHEATING 

Reheating a cooled air stream using heat from liquid refrigerant en route to a direct-expansion cooling coil is quite desirable from an efficiency standpoint, How To Choose A Professional Dehumidifier as it requires only a single coil to accomplish what the previous arrangements do with two heat-transfer devices. Figure 8 illustrates this dehumidification enhancement. 

The temperature of the refrigerant liquid supplied to a direct-expansion coil often is in the 90- to 115-F range. The reheat coil uses this warm liquid to reheat the cold air stream while simultaneously subcooling the liquid refrigerant. The subcooled liquid refrigerant then enters the direct expansion coil and, because it is subcooled, How To Choose A Professional Dehumidifier increases the latent and total capacity of the cooling coil. 

Figure 9 shows compressor-condenser capacity with and without subcooling as well as evaporator-cooling-coil capacity. The reheat energy is free and the penalties of increased refrigeration How To Choose A Professional Dehumidifier or the expense of additional cooling energy are avoided. The net effect of this cycle is identical to that of the run-around enhancements with two beneficial exceptions.

A precooling coil is not required How To Choose A Professional Dehumidifier and (2) the row depth of the reheat coil is less than that of the heat pipe or run-around coil. A limitation of this method is the small amount of heat available. For example, in an R-22 system with liquid refrigerant entering the reheat coil at 95 F and leaving at 55 F, the total amount of heat available is 2000 Btu per ton-hr. 

Assuming an air-circulation rate of 350 cfm per ton, this results in a 5.2-F rise in air temperature across. the reheat coil. With 100-percent outside-air systems at less than 200 cfm per ton, the temperature rise is approximately 10 F. If the reheat from this coil is not sufficient, How To Choose A Professional Dehumidifier an additional heating coil using some other form of energy is required. 

This adds to the first cost, the space required, and the control complexity. A 5-F rise in air temperature in a 350-cfm-per-ton system may appear small; however, when this system is retrofitted to an existing unit, How To Choose A Professional Dehumidifier the amount of moisture removal increases by approximately 50 percent because of the combined effects of greater moisture removal per minute by the cooling/dehumidifying coil and longer run time attributed to the increase in supply-air temperature by the reheat coil. 

Figure 8 shows the piping of the refrigerant-liquid/reheat coil. The reheat coil is part of the refrigerant liquid line, How To Choose A Professional Dehumidifier with the additional refrigerant charge equal to the volume of the reheat-coil tubes and additional piping. Some manufacturers balk at installing a liquid-subcooling/air-reheating coil in a system (the effect of the coil on the refrigeration system is the same as that of an additional 20 or 30 ft of liquid line in a 60-F room). 

If a winter heating source is located upstream from the refrigerant-liquid-reheat coil, then the refrigerant circuit must be checked to ensure that the refrigerant has a path to the receiver How To Choose A Professional Dehumidifier and is not blocked by isolation valves. If the liquid-refrigerant coil is isolated by line valves during the winter, then high pressures could be a problem. 

Advantages. The advantages of refrigerant-subcooling/air-reheating dehumidification are: There are no water circuits to freeze How To Choose A Professional Dehumidifier or ethylene-glycol charges to maintain. Electrical connections are not required. Controls are not required for most systems. Only a single coil is required in the air stream leaving the main cooling coil. 

Air resistance is approximately half of that of the previous enhancements. Disadvantages. Disadvantages of refrigerant-subcooling/air-reheating dehumidification are: The cost of the additional refrigerant charge and, in retrofit applications, the isolation, evacuation, How To Choose A Professional Dehumidifier and recharging of the refrigerant circuit. 

Possible bursting pressures if relief provisions are not made when the coil is located downstream from the heating apparatus. Concerns about refrigerant migration and inventory management, How To Choose A Professional Dehumidifier particularly in heat-pump refrigeration cycles. Controls, if required, add expense.

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