COMPARING UNITS Consider rated supply-air dew-point temperature and energy efficiency at a range of design conditions. Low dew-point temperature (less than 50 F) is de-sirable. Very low dew-point-temperature(less than 40 to 45 F) supply air can meet a building’s entire latent load; however, units capable of providing such air are more expensive. Even a 2-F difference in dew point between competing products is significant. Desired leaving dew point depends on how much ventilation and internal latent load will be met by downstream components, such as chilled-water coils. A building’s HVAC system can be designed so that a desiccant unit pre-dehumidifies ventilation air, with the cooling coil finishing the process—for example, 58-F-dew-point air leaving the desiccant unit and 50-F-dew-point air leaving the cooling coil. 3 Alternatively, the desiccant unit could provide all dehumidification, leaving the cooling coil dry—for example, 50-F-dew-point air entering and leaving the coil. In this case, the desiccant unit meets the building’s entire latent load.
DESIRABLE FEATURES Cost can vary considerably by model and manufacturer. Consider maintain-ability, looking for water-washable rotors that retain like-new performance. Compare construction and materials, looking for durable rotor substrate media, stainless-steel or aluminum rotor-frame/cassette parts for resistance to corrosion, and high-percent desiccant loading by total media mass. Lastly, consider service support and the length and terms of the warranty. Sophisticated controls are important in minimizing operating costs. Variable control of regeneration temperature and wheel rotational speed is preferred over on/off control, as is modulating control of heat input (gas burner or steam/water coil). A proportional space humidistat is preferred over an on/off humidistat because it eliminates short cycling during low-load conditions. Compatibility with building-automation systems and factory-installed temperature and humidity sensors is a definite plus. Industrial units are designed with 1⁄8 -in. aluminum or stainless-steel cabinets, sturdier damper vanes and actuators, premium-efficiency motors, industrial-grade controls, sealed rotor drives and bearings, and desiccants that provide lower leaving-air dew-point temperature and/or higher energy efficiency. Post-cooling using heat pipes, a sensible-heat wheel, and/or indirect evaporative cooling adds to unit first cost, but signifi-cantly reduces energy cost for a lower life-cycle cost.When comparing ratings and specifications, look for: • Low internal static-pressure drop—less than 2.50 in. wg total. • High reactivation-heat fuel effi-ciency—greater than 90 percent, whichmeans direct-fired is preferred over indirect. • Low electric-power kilowatts, low internal static pressure, low motor horse-power, premium-efficiency motors,no electric-resistance heat, and no DX cooling.
Desiccant dehumidifiers are used for lower-dew-point (below 50 to 55 F) applications, such as frozen-food display, plastics production, and records storage. Places they are most likely to be found include supermarkets, ice arenas, water-treatment facilities, surgical suites, and museums. Active desiccant dehumidifiers require an external heat source for regeneration, while passive units exchange moisture and heat between fresh- and exhaust-air streams.
Active desiccant units are most cost-effective when they use low-grade heat for regeneration. This is relatively inexpensive heat from sources such as microturbine exhaust and direct-expansion (DX) hot gas. A lower leaving dew point will be obtained with a higher regeneration temperature, lower process entering dry bulb, lower process entering dew point, and, to a lesser extent, lower process face velocity and entering regeneration dew point. The process leaving dry bulb will vary as these conditions change. Desiccant systems are most beneficial where thermal energy is readily available, the price of electricity is high, and the sensible-load fraction is low (sensible- heat ratio [SHR] less than 0.65). For comfort-conditioning and process uses, the most common desiccant dehumidifiers use a rotating wheel. Desiccant units and rotors—the honeycomb-shaped, desiccant-media matrices formed into wheels—are very much project- and manufacturer-specific, so application engineering is especially critical for a cost-effective project. Performance-rating standards were not available until 1998, so the certified apples-to-apples ratings engineers take for granted with other HVAC equipment usually are not available with desiccant equipment. Nonetheless, desiccant units are becoming more standardized. In the right applica- tion, a properly applied, well-engineered system can pay for itself in reduced cooling tonnage and energy savings, while providing consistent comfort under all weather conditions.
CONFIGURATION The heart of a solid desiccant-wheel unit is the rotor. Supply air passes through one sector of the rotor and is dehumidified and heated. The rotor turns slowly into the reactivation-air stream, which dries the desiccant and exhausts the moisture from the unit. By itself, the rotor performs no useful cooling. It merely converts latent load into high-temperature sensible heat that can be rejected with minimal energy input. Because of latent heat and transfer from the regeneration stream, humidified process air leaves the rotor at a temperature much higher than that of the inlet. The temperature is 6- to 9-F hotter for each 10 grains of moisture reduction. This temperature rise mostly represents the conversion CONFIGURATION The heart of a solid desiccant-wheel unit is the rotor. Supply air passes through one sector of the rotor and is dehumidified and heated. The rotor turns slowly into the reactivation-air stream, which dries the desiccant and exhausts the moisture from the unit. By itself, the rotor performs no useful cooling. It merely converts latent load into high- temperature sensible heat that can be rejected with minimal energy input. Because of latent heat and transfer from the regeneration stream, dehumidified process air leaves the rotor at a temperature much higher than that of the inlet. The temperature is 6- to 9-F hotter for each 10 grains of moisture reduction. This temperature rise mostly represents the conversion
this is formula ANSI/ASHRAE STANDARD 139-2007 Method of Testing for Rating Desiccant Dehumidifiers Utilizing Heat for the Regeneration Process September 17, 2007 The corrections listed in this errata sheet apply to the first printing of ANSI/ASHRAE Standard 139-2007. The outside back cover marking identifying the first printing is “86466 PC 7/07”. Page Erratum 8 Section 6.9.2 Heat Input – Gas Fuel. Replace the equation(s) for QS with the following: (SI Units) QS = [Hg x (Mf - Mi) x (273.2 +20) x P] / [(T + 273.2) x 101.325 x Time x 60], kJ/s (I-P Units) QS = [Hg x (Mf - Mi) x (459.3 +68) x P] / [(T + 459.3) x 14.696 x Time x 1/60], Btu/h
SELECTION Manufacturer selection charts typically show dehumidification performance as “grains of depression” reduced absolute humidity in grains of moisture per pound of dry air. Unit size is based on airflow in cubic feet per minute. Of greater interest to most designers is supply-air dew-point temperature (in degrees Fahrenheit), latent cooling capacity (in British thermal units per hour), and energy efficiency (coefficient of performance [COP]). Often, these values must be derived from data in manufacturers’ product literature. Of course, a unit with higher energy efficiency is desirable because the cost of operating it will be lower. For a fair comparison, calculate COP by dividing total capacity (sensible plus latent) by total energy input (waste heat, natural gas, plus all electric). Some ratings simply are latent capacity divided by heat input, which is misleading because sensible capacity often is negative (heating), and the electric fan power needed to provide 2- to 3-in.- wc internal static pressure is considerable. Energy- efficiency ratings consider only electric input to fans and compressors, if there are any. The COP of desiccant equipment varies greatly with entering-air conditions, so it is important to calculate COP at a range of design conditions. Even better is to use a joint-frequency bin analysis or an hourly computer simulation. For most fresh-air-ventilation applications, a design dew-point temperature or latent cooling load must be met at various entering-air conditions. Table 1 shows standard Air-Conditioning and Refrigeration Institute (ARI) rating conditions, which some manufacturers still do not follow.
Heat Input – Gas Fuel. Replace the equation(s) for QS with the following: (SI Units) QS = [Hg x (Mf - Mi) x (273.2 +20) x P] / [(T + 273.2) x 101.325 x Time x 60], kJ/s (I-P Units) QS = [Hg x (Mf - Mi) x (459.3 +68) x P] / [(T + 459.3) x 14.696 x Time x 1/60], Btu/h
Our Digital E-learning program with free internet based recordings and live talks makes our web based instructing for PGCET an exceptionally eminent one. We are liked by practically all new understudies these days since we have a prestigious name in the training area. Online PGCET Coaching
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ReplyDeletehow to replace desiccant rotor
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ReplyDeleteCOMPARING UNITS
DeleteConsider rated supply-air dew-point temperature and energy efficiency at a range of design conditions. Low dew-point temperature (less than 50 F) is de-sirable. Very low dew-point-temperature(less than 40 to 45 F) supply air can meet a building’s entire latent load; however, units capable of providing such air are more expensive. Even a 2-F difference in dew point between competing products is significant. Desired leaving dew point depends on how much ventilation and internal
latent load will be met by downstream components, such as chilled-water coils. A building’s HVAC system can be
designed so that a desiccant unit pre-dehumidifies ventilation air, with the cooling coil finishing the process—for example, 58-F-dew-point air leaving the desiccant unit and 50-F-dew-point air leaving the cooling coil. 3 Alternatively, the desiccant unit could provide all dehumidification, leaving the cooling coil dry—for example, 50-F-dew-point air entering and leaving the coil. In this case, the desiccant unit meets the building’s entire latent load.
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ReplyDeleteHow to Buy industrial dehumidifier wheel
ReplyDeleteDESIRABLE FEATURES
DeleteCost can vary considerably by model and manufacturer. Consider maintain-ability, looking for water-washable rotors that retain like-new performance. Compare construction and materials, looking for durable rotor substrate media, stainless-steel or aluminum rotor-frame/cassette parts for resistance to corrosion, and high-percent desiccant loading by total media mass. Lastly, consider service support and the length and terms of the warranty. Sophisticated controls are important in minimizing operating costs. Variable control of regeneration temperature and wheel rotational speed is preferred over on/off control, as is modulating
control of heat input (gas burner or steam/water coil). A proportional space humidistat is preferred over an on/off humidistat because it eliminates short cycling during low-load conditions. Compatibility with building-automation systems and factory-installed temperature
and humidity sensors is a definite plus. Industrial units are designed with 1⁄8 -in. aluminum or stainless-steel cabinets, sturdier damper vanes and actuators, premium-efficiency motors, industrial-grade controls, sealed rotor drives and bearings, and desiccants that provide lower leaving-air dew-point temperature and/or higher energy efficiency. Post-cooling using heat pipes, a sensible-heat wheel, and/or indirect evaporative cooling adds to unit first cost, but signifi-cantly reduces energy cost for a lower
life-cycle cost.When comparing ratings and specifications, look for:
• Low internal static-pressure drop—less than 2.50 in. wg total.
• High reactivation-heat fuel effi-ciency—greater than 90 percent, whichmeans direct-fired is preferred over
indirect.
• Low electric-power kilowatts, low internal static pressure, low motor horse-power, premium-efficiency motors,no electric-resistance heat, and no DX cooling.
How to Buy industrial desiccant dehumidifier rotor in lower cost and best quality
ReplyDeleteHow to Buy industrial desiccant dehumidifier rotor in best price and best quality
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ReplyDeleteWhere can we use desiccant dehumidifier rotors
ReplyDeleteDesiccant dehumidifiers are used for lower-dew-point (below 50 to 55 F) applications, such as frozen-food
Deletedisplay, plastics production, and records storage.
Places they are most likely to be found include supermarkets, ice arenas, water-treatment facilities,
surgical suites, and museums.
Active desiccant dehumidifiers require an external
heat source for regeneration, while passive units
exchange moisture and heat between fresh- and
exhaust-air streams.
What is ACTIVE UNITS in Desiccant dehumidifier
ReplyDeleteActive desiccant units are most cost-effective
Deletewhen they use low-grade heat for regeneration.
This is relatively inexpensive heat from sources
such as microturbine exhaust and direct-expansion
(DX) hot gas. A lower leaving dew point will be
obtained with a higher regeneration temperature,
lower process entering dry bulb, lower process
entering dew point, and, to a lesser extent, lower
process face velocity and entering regeneration
dew point. The process leaving dry bulb will
vary as these conditions change. Desiccant systems
are most beneficial where thermal energy is
readily available, the price of electricity is high,
and the sensible-load fraction is low (sensible-
heat ratio [SHR] less than 0.65).
For comfort-conditioning and process uses,
the most common desiccant dehumidifiers use a rotating wheel. Desiccant units and rotors—the
honeycomb-shaped, desiccant-media matrices
formed into wheels—are very much project- and
manufacturer-specific, so application engineering
is especially critical for a cost-effective project.
Performance-rating standards were not available
until 1998, so the certified apples-to-apples ratings
engineers take for granted with other HVAC
equipment usually are not available with desiccant
equipment. Nonetheless, desiccant units are
becoming more standardized. In the right applica-
tion, a properly applied, well-engineered system
can pay for itself in reduced cooling tonnage
and energy savings, while providing consistent
comfort under all weather conditions.
What is working of desiccant dehumidifier rotor
ReplyDeleteCONFIGURATION
DeleteThe heart of a solid desiccant-wheel unit is the rotor. Supply air passes through one sector of the rotor and is dehumidified and heated. The rotor turns slowly into the reactivation-air stream, which dries the desiccant and exhausts the moisture from the unit. By itself, the rotor performs no useful cooling. It merely converts latent load into high-temperature sensible heat that can be rejected with minimal energy input. Because of latent heat and transfer from the regeneration stream, humidified process air leaves the rotor at a temperature much higher than that of the inlet. The temperature is 6- to 9-F hotter for each 10 grains of moisture reduction. This temperature rise mostly represents the conversion CONFIGURATION
The heart of a solid desiccant-wheel unit is the
rotor. Supply air passes through one sector of the
rotor and is dehumidified and heated. The rotor
turns slowly into the reactivation-air stream, which
dries the desiccant and exhausts the moisture from
the unit. By itself, the rotor performs no useful cooling. It merely converts latent load into high-
temperature sensible heat that can be rejected with minimal energy input.
Because of latent heat and transfer from the regeneration stream, dehumidified process air leaves the rotor at a temperature much higher than that of the inlet. The temperature is 6- to 9-F hotter for each 10 grains of moisture reduction. This temperature rise mostly represents the conversion
this is formula
DeleteANSI/ASHRAE STANDARD 139-2007
Method of Testing for Rating Desiccant Dehumidifiers
Utilizing Heat for the Regeneration Process
September 17, 2007
The corrections listed in this errata sheet apply to the first printing of ANSI/ASHRAE
Standard 139-2007. The outside back cover marking identifying the first printing is
“86466 PC 7/07”.
Page Erratum
8 Section 6.9.2 Heat Input – Gas Fuel. Replace the equation(s) for QS with the
following:
(SI Units)
QS = [Hg x (Mf - Mi) x (273.2 +20) x P] / [(T + 273.2) x 101.325 x Time x 60], kJ/s
(I-P Units)
QS = [Hg x (Mf - Mi) x (459.3 +68) x P] / [(T + 459.3) x 14.696 x Time x 1/60], Btu/h
How to select best desiccant dehumidifier
ReplyDeleteSELECTION
DeleteManufacturer selection charts typically show dehumidification performance as “grains of depression” reduced absolute humidity in grains of moisture per pound of dry air. Unit size is based on airflow in cubic feet per minute. Of greater interest to most designers is supply-air dew-point temperature (in degrees Fahrenheit), latent cooling capacity (in British thermal units per hour), and energy efficiency (coefficient of performance [COP]). Often, these values must be derived
from data in manufacturers’ product literature.
Of course, a unit with higher energy efficiency is desirable because the cost of operating it will be lower. For a fair comparison, calculate COP by dividing total capacity (sensible plus latent) by total energy input (waste heat, natural gas, plus all electric). Some ratings simply are latent capacity divided by heat input, which is misleading because sensible capacity often is negative (heating), and the electric fan power needed to provide 2- to 3-in.- wc internal static pressure is considerable. Energy- efficiency ratings consider only electric input to fans and compressors, if there are any. The COP of desiccant equipment varies greatly with entering-air conditions, so it is important to calculate COP at a range of design conditions. Even better is to use a joint-frequency bin analysis or an hourly computer simulation.
For most fresh-air-ventilation applications, a design dew-point temperature or latent cooling load must be met at various entering-air conditions. Table 1 shows standard Air-Conditioning and Refrigeration Institute (ARI) rating conditions, which some manufacturers still do not follow.
What is Method of Testing for Rating Desiccant Dehumidifiers Utilizing Heat for the Regeneration Process
ReplyDeleteHeat Input – Gas Fuel. Replace the equation(s) for QS with the following:
Delete(SI Units)
QS = [Hg x (Mf - Mi) x (273.2 +20) x P] / [(T + 273.2) x 101.325 x Time x 60], kJ/s
(I-P Units)
QS = [Hg x (Mf - Mi) x (459.3 +68) x P] / [(T + 459.3) x 14.696 x Time x 1/60], Btu/h
Our Digital E-learning program with free internet based recordings and live talks makes our web based instructing for PGCET an exceptionally eminent one. We are liked by practically all new understudies these days since we have a prestigious name in the training area. Online PGCET Coaching
ReplyDelete