Bryant 551B, 558F, 551A manual APPLICATION DATA cont, Applications

APPLICATION DATA (cont)

c. HUMIDITY DAMAGE — Humidity causes property damage, such as stained wallpaper and ceiling tiles. Humidity can also damage books and artwork, and cre- ate strong odors in carpets. In addition, humidity can contribute to unacceptable product quality in industrial processes.

d. IMPROPER VENTILATION — Buildings in hot and humid geographical areas cannot be properly ventilated due to high humidity levels outdoors, resulting in poor indoor-air quality.

e. EQUIPMENT INEFFICIENCY — Humidity can cause inefficient operation of refrigerators and freezers.

f.INCREASED ENERGY COSTS — Because of high humidity levels and less comfortable conditions, thermo- stat set points are lowered to force the HVAC (heating, ventilation, and air conditioning) equipment to run longer and work harder to lower the humidity levels. Also, in an attempt to control humidity, system designers typically oversize HVAC equipment and add reheat capability to get the desired latent capacity. This results in higher ini- tial equipment costs, as well as increased energy expenses throughout the life of the unit.

Applications

There are many different rooftop unit applications that are susceptible to problems caused by high humidity levels. Some common applications include:

a. RESTAURANTS — The kitchen areas of restaurants have many humidity-producing activities, such as dish washing and cooking.

b.SUPERMARKETS — High humidity levels cause ineffi- ciency in operation of refrigeration and freezer systems.

c.MUSEUMS AND LIBRARIES — Humidity can damage books and artwork.

d.GYMNASIUMS, LOCKER ROOMS, AND HEALTH CLUBS — Shower areas and human perspiration cause uncomfortable occupied space conditions.

e.HOT AND HUMID CLIMATES — The southeastern United States is a good example of this application. The Perfect Humidity dehumidification package becomes particularly useful when increased amounts of the hot and humid outdoor air need to be brought into the build- ing for proper ventilation.

13.PERFECT HUMIDITY DEHUMIDIFICATION PACKAGE DESIGN EFFECTS — To fully understand the operation of the Perfect Humidity dehumidification package, refer to the pressure enthalpy curve, and analyze the Perfect Humidity package effects on the refrigerant in the rooftop unit. The pressure enthalpy curve shows the refrigerant cycle for a rooftop unit.

Standard Unit Refrigerant Cycle

At point no. 1 in the pressure enthalpy curve, vapor leaving the compressor at a high pressure and a high temperature enters the condenser. The condenser removes heat from the refriger- ant, lowers its temperature, and changes it to a liquid. At point no. 2, the liquid leaves the condenser and enters a fixed expan- sion device that lowers the pressure of the refrigerant. At point no. 3, the liquid enters the evaporator coil, where the refrigerant increases in temperature and changes back to a vapor. At point no. 4, the vapor leaves the evaporator and reenters the compressor.

Refrigerant Cycle Using Perfect Humidity™ Dehumidification Package

When a subcooler coil is added to the rooftop unit, the refriger- ant is affected in such a way that the unit latent capacity is increased. The refrigerant cycle follows the same path from point no. 1 to point no. 2 as the standard refrigerant cycle with- out a subcooler (see the pressure enthalpy curve). However, at point no. 2, the liquid refrigerant enters the subcooler coil where the temperature is lowered further. At point no. 2A, this sub- cooled liquid enters the TXV, which drops the pressure of the liquid. At point no. 2B, the liquid enters the fixed orifice metering device. The refrigerant leaves this device as a saturated vapor and enters the evaporator at point no. 2C. The improved refrig- eration effect can now be seen between point no. 2C and point no. 3. The increase in the total refrigeration effect is the addi- tional enthalpy gained from point no. 2C to point no. 3. However, the subcooler coil rejects this added refrigeration effect to the air downstream of the evaporator coil, thus maximizing the over- all latent effect. This improved latent effect is a direct result of the addition of the Perfect Humidity subcooler coil to the refrig- erant cycle.

Latent Capacity Effects

Refer to the psychrometric chart to see how the sensible heat factor decreases when the optional Perfect Humidity dehumidifi- cation package is installed. This chart contains data for the 5-ton unit operation, both with and without the Perfect Humidity package, at 1750 cfm. Point no. 1 on the chart represents the return-air dry bulb (80 F) and wet bulb (67 F) conditions. Point no. 2 represents the supply-air conditions for a standard rooftop unit without the Perfect Humidity dehumidification package. Point no. 3 represents the supply-air conditions for a rooftop unit with the Perfect Humidity package. By connecting point no. 1 and point no. 2 on the chart and finding the intersection on the sensible heat factor scale, the sensible heat factor is 0.73. Con- nect point no. 1 and point no. 3, and see that the sensible heat factor is 0.58. This is a 17.5% increase in latent capacity for the given conditions. This increase in latent capacity allows the rooftop units to remove more moisture from the conditioned space; thus lowering the humidity levels.

Dehumidification Effects

Further evidence of dehumidification can be seen by analyzing the pounds of water per pound of dry air found in the supply air. At point no. 2 in the psychrometric chart, there are 65 grains (0.0092 lb) of moisture per pound of dry air. At point no. 3, there are 58 grains (0.0083 lb) of moisture per pound of dry air. This is a 12.1% decrease in the amount of water in the supply air.

14.PERFECT HUMIDITY DEHUMIDIFICATION PACKAGE OPERATING PERFORMANCE — Perfect Humidity dehu- midification package operation does not affect the electrical data. The electrical data remains the same either with or without the Perfect Humidity package.

The operating and shipping weights will be slightly increased with the addition of the Perfect Humidity sub- cooler. See the Physical Data table for added base unit weight with this option.

Refer to cooling performance data, both with and without the Perfect Humidity dehumidification package. Note the greatly improved latent capacity with the Perfect Humidity dehumidification package.

Static pressure is also slightly affected by the addition of the Perfect Humidity dehumidification package. See Static Pressure Drop table on page 94 when using this option.

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