ASHRAE Journal - December 2009 - 62

Technical Topics Refrigerant Subcooling Air-Reheating Coil °F Inactive 57.5 DB 55.2 DP °F Inactive 57.5 DB 55.2 DP °F Active 62.2 DB 51.9 DP °F Active 53.9 DB 51.9 DP 115°F Liquid 75°F Liquid Figure 1: Inactive and active LSCARH dehumidification enhancement. 115°F Liquid Line Solenoid or Manual Valve Evaporator °F Inactive 80.0 DB 60.3 DP °F Active 80.0 DB 60.3 DP Inactive 3.04 lb/h Condenser Compressor Moisture Removal Active 4.72 lb/h *Increase due to longer 1.21 lb/h* runtime because of higher Total 5.93 lb/h leaving DB. Increase 95% Input parameters: R-410A, 0.7 isentropic compressor efficiency, no line or HX pressure drop, 9°F evaporator superheat. Evaporator airflow 350 cfm for a normalized 1 ton nominal compressor. Old Dehumidification Technology Liquid Subcooling/Air Reheating By Donald P. Gatley, P.E., Fellow/Life Member ASHRAE; and Jason LeRoy or whatever reasons, refrigerant liquid subcooling/air reheating, a pared with other dehumidification methods. This recuperative enhancement designated herein liquid subcooling/air reheating (LSCARH) uses only a single coil to accomplish what other recuperative arrangements do with two added heat transfer devices (one precooling and one reheating). Figure 1 is an example of this dehumidification enhancement showing a 95% increase in moisture removal for a system using refrigerant R-410A. R-410A properties are more beneficial than R-22 in an identical LSCARH cycle, which only shows a 62% increase in moisture removal. The temperature of the refrigerant liquid supplied to a direct expansion coil is often in the 90°F (32.2°C) to 115°F (46.1°C) range. The LSCARH coil transfers heat from the warm refrigerant liquid to the cold airstream leaving the direct expansion cooling coil while simultaneously subcooling the liquid refrigerant. The subcooled liquid refrigerant then enters the direct expansion coil and, because it is subcooled, the cooling coil capacity is increased. The reheat energy is free, except for the additional fan power associated with the ashrae.org 70-old dehumidification enhancement technology, has been largely forgotten or ignored. It has been successfully used in food stores by three manufacturers and in single packaged air conditioners by a major manufacturer. Its best application may be in residential air conditioning for lowering humidity. Surprisingly, system moisture removal in the subcooling mode with refrigerant R-410A is approximately 50% greater than with R-22. Reheat of a cooled airstream using the heat from refrigerant liquid on its way to a direct expansion cooling coil is desirable from an efficiency standpoint when com62 ASHRAE Journal air-side pressure drop of the added coil and a minor increase in compressor power due to lowered evaporator pressure. The net effect of this cycle is similar to the runaround enhancements discussed in an August 2009 ASHRAE Journal1 article with two beneficial exceptions: No precooling coil is required; and the row depth of the reheat coil is less than the row depth of the two-heat pipe or runaround coil. Should a LSCARH be chosen in preference to other recuperative dehumidification systems? Yes and no. A limitation of LSCARH is the limited amount of heat available. In the Figure 1 example, liquid refrigerant at 115°F (46.1°C) entering the reheat coil and leaving at 75°F (23.9°C), the total amount of heat available is 3,209 Btu/h (940 W) for the normalized 1 ton (3.5 kW) system. If this amount of reheat is not sufficient, an additional heating coil and heat source is required. The available reheat energy may appear small. However, the amount of moisture removal in the Figure 1 example is increased by 95% because of the combined effects of (a) greater moisture removal per minute by the cooling-dehumidifying coil; and (b) longer runtime because of the increase in supply air temperature leaving the reheat coil on its way to the conditioned space. December 2009

ASHRAE Journal - December 2009

Table of Contents for the Digital Edition of ASHRAE Journal - December 2009

ASHRAE Journal - December 2009
Contents
Commentary
Industry News
Letters
Meetings and Shows
ASHRAE Building EQ Program
Feature Articles
A Closer Look at Chiller Ratings
Cooling With Less Air: Using Underfloor Air Distribution and Chilled Beams
Cooling Concrete: Containerized Water Chilling Plant
Geothermal for Community Center
Anniversary Feature: Air-Recovery System Versus Conventional Air Conditioning
Technical Topics
New Product Preview
Products
Emerging Technologies
Washington Report
People
Special Products
2009 Feature Articles Indices
Classified Advertising
Advertisers Index
ASHRAE Journal - December 2009 - ASHRAE Journal - December 2009
ASHRAE Journal - December 2009 - Cover2
ASHRAE Journal - December 2009 - 1
ASHRAE Journal - December 2009 - 2
ASHRAE Journal - December 2009 - Contents
ASHRAE Journal - December 2009 - 4
ASHRAE Journal - December 2009 - Commentary
ASHRAE Journal - December 2009 - Industry News
ASHRAE Journal - December 2009 - 7
ASHRAE Journal - December 2009 - 8
ASHRAE Journal - December 2009 - 9
ASHRAE Journal - December 2009 - 10
ASHRAE Journal - December 2009 - Letters
ASHRAE Journal - December 2009 - 12
ASHRAE Journal - December 2009 - 13
ASHRAE Journal - December 2009 - 14
ASHRAE Journal - December 2009 - 15
ASHRAE Journal - December 2009 - Meetings and Shows
ASHRAE Journal - December 2009 - 17
ASHRAE Journal - December 2009 - Feature Articles
ASHRAE Journal - December 2009 - 19
ASHRAE Journal - December 2009 - 20
ASHRAE Journal - December 2009 - 21
ASHRAE Journal - December 2009 - A Closer Look at Chiller Ratings
ASHRAE Journal - December 2009 - 23
ASHRAE Journal - December 2009 - 24
ASHRAE Journal - December 2009 - 25
ASHRAE Journal - December 2009 - 26
ASHRAE Journal - December 2009 - 27
ASHRAE Journal - December 2009 - 28
ASHRAE Journal - December 2009 - 29
ASHRAE Journal - December 2009 - 30
ASHRAE Journal - December 2009 - 31
ASHRAE Journal - December 2009 - 32
ASHRAE Journal - December 2009 - 33
ASHRAE Journal - December 2009 - Cooling With Less Air: Using Underfloor Air Distribution and Chilled Beams
ASHRAE Journal - December 2009 - 35
ASHRAE Journal - December 2009 - 36
ASHRAE Journal - December 2009 - 37
ASHRAE Journal - December 2009 - 38
ASHRAE Journal - December 2009 - 39
ASHRAE Journal - December 2009 - 40
ASHRAE Journal - December 2009 - 41
ASHRAE Journal - December 2009 - Cooling Concrete: Containerized Water Chilling Plant
ASHRAE Journal - December 2009 - 43
ASHRAE Journal - December 2009 - 44
ASHRAE Journal - December 2009 - 45
ASHRAE Journal - December 2009 - 46
ASHRAE Journal - December 2009 - 47
ASHRAE Journal - December 2009 - Geothermal for Community Center
ASHRAE Journal - December 2009 - 49
ASHRAE Journal - December 2009 - 50
ASHRAE Journal - December 2009 - 51
ASHRAE Journal - December 2009 - Anniversary Feature: Air-Recovery System Versus Conventional Air Conditioning
ASHRAE Journal - December 2009 - 53
ASHRAE Journal - December 2009 - 54
ASHRAE Journal - December 2009 - 55
ASHRAE Journal - December 2009 - 56
ASHRAE Journal - December 2009 - 57
ASHRAE Journal - December 2009 - 58
ASHRAE Journal - December 2009 - 59
ASHRAE Journal - December 2009 - 60
ASHRAE Journal - December 2009 - 61
ASHRAE Journal - December 2009 - Technical Topics
ASHRAE Journal - December 2009 - 63
ASHRAE Journal - December 2009 - 64
ASHRAE Journal - December 2009 - New Product Preview
ASHRAE Journal - December 2009 - 66
ASHRAE Journal - December 2009 - 67
ASHRAE Journal - December 2009 - 68
ASHRAE Journal - December 2009 - 69
ASHRAE Journal - December 2009 - 70
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ASHRAE Journal - December 2009 - 111
ASHRAE Journal - December 2009 - 112
ASHRAE Journal - December 2009 - 113
ASHRAE Journal - December 2009 - Products
ASHRAE Journal - December 2009 - 115
ASHRAE Journal - December 2009 - 116
ASHRAE Journal - December 2009 - Emerging Technologies
ASHRAE Journal - December 2009 - Washington Report
ASHRAE Journal - December 2009 - 119
ASHRAE Journal - December 2009 - People
ASHRAE Journal - December 2009 - Special Products
ASHRAE Journal - December 2009 - 2009 Feature Articles Indices
ASHRAE Journal - December 2009 - 123
ASHRAE Journal - December 2009 - 124
ASHRAE Journal - December 2009 - 125
ASHRAE Journal - December 2009 - Classified Advertising
ASHRAE Journal - December 2009 - 127
ASHRAE Journal - December 2009 - Advertisers Index
ASHRAE Journal - December 2009 - Cover3
ASHRAE Journal - December 2009 - Cover4
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