ASHRAE Journal - April 2010 - 39

ventilation and larger-than-necessary equipment. This may inflate installed costs and can result in excessive energy use. To minimize the impact of safety factors on installed cost and energy use, the recommendations of this author are as follows: 1. Avoid applying safety factors to zone population (Pz) when calculating the required outdoor airflow (Voz) and design latent load (qLspace) for each zone. Estimate population and loads as accurately as possible, then select a dedicated OA unit that has reserve (or extra) airflow and/or dehumidification capacity. This may result in the selection of larger equipment, which can increase installed cost, but there are often energy-related benefits associated with a larger unit. The example in Table 5 (see Page 36) shows two dedicated OA units selected to deliver the same airflow and provide the same dehumidification capacity. The larger casing size has more reserve capacity to accommodate unexpected loads and the need for increased airflow or dehumidification. The larger unit, when operating at the same design airflow as the smaller unit, has a lower airside pressure drop across both the cooling coil and the total-energy wheel, resulting in less fan power. In addition, the lower face velocity across the wheel results in higher effectiveness and more energy-recovery capacity.

However, selection of the dedicated OA unit is influenced by the type of dedicated OA equipment being used. For example, DX dehumidification equipment may be less tolerant of being selected with reserve capacity than chilled water or desiccant-based equipment, because of the need to properly match airflow range with the operating envelope of the refrigeration equipment. 2. When defining the design outdoor conditions (Woa) and the target space humidity level (Wsp) analyze the impact of these decisions up front and share that information with the owner to assist in making the final decisions. Using the same four-classroom example in Jacksonville, Fla. (Table 3), Figures 4 and 5 (see Page 36) demonstrate the impact of the selected ASHRAE design dew-point condition (0.4%, 1%, or 2%) and the desired upper humidity limit for the occupied space (Wsp) on the required dehumidification capacity (qL) of the dedicated OA unit. This is the capacity needed to offset the entire ventilation latent load plus all of the indoor latent loads. (Figure 4 shows the required capacity if the unit has no exhaustair energy recovery, while Figure 5 shows the required capacity if the unit includes a total-energy recovery device with 70% latent effectiveness.) These figures emphasize the following points:

www.info.hotims.com/30303-33

April	2010	

ASHRAE	Journal	

39



ASHRAE Journal - April 2010

Table of Contents for the Digital Edition of ASHRAE Journal - April 2010

ASHRAE Journal - April 2010
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
The Science of Evaporation is Key to Defense in Murder Trial
Selecting DOAS Equipment with Reserve Capacity
Technology Award Case Studies: Greening Hospitals
Technology Award Case Studies: Sustainable Remedy for Hospital
Building Sciences
Emerging Technologies
Technical Topics: Selecting Efficient Fans
Technical Topics: Dual-Capacity Heat Pumps
IAQ Applications
International Column
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2010 - Intro
ASHRAE Journal - April 2010 - ASHRAE Journal - April 2010
ASHRAE Journal - April 2010 - Cover2
ASHRAE Journal - April 2010 - 1
ASHRAE Journal - April 2010 - 2
ASHRAE Journal - April 2010 - Contents
ASHRAE Journal - April 2010 - Commentary
ASHRAE Journal - April 2010 - 5
ASHRAE Journal - April 2010 - Industry News
ASHRAE Journal - April 2010 - 7
ASHRAE Journal - April 2010 - 8
ASHRAE Journal - April 2010 - 9
ASHRAE Journal - April 2010 - 10
ASHRAE Journal - April 2010 - 11
ASHRAE Journal - April 2010 - 12
ASHRAE Journal - April 2010 - 13
ASHRAE Journal - April 2010 - 14
ASHRAE Journal - April 2010 - 15
ASHRAE Journal - April 2010 - 16
ASHRAE Journal - April 2010 - 17
ASHRAE Journal - April 2010 - Letters
ASHRAE Journal - April 2010 - 19
ASHRAE Journal - April 2010 - Meetings and Shows
ASHRAE Journal - April 2010 - 21
ASHRAE Journal - April 2010 - The Science of Evaporation is Key to Defense in Murder Trial
ASHRAE Journal - April 2010 - 23
ASHRAE Journal - April 2010 - 24
ASHRAE Journal - April 2010 - 25
ASHRAE Journal - April 2010 - 26
ASHRAE Journal - April 2010 - 27
ASHRAE Journal - April 2010 - 28
ASHRAE Journal - April 2010 - 29
ASHRAE Journal - April 2010 - Selecting DOAS Equipment with Reserve Capacity
ASHRAE Journal - April 2010 - 31
ASHRAE Journal - April 2010 - 32
ASHRAE Journal - April 2010 - BRC1
ASHRAE Journal - April 2010 - BRC2
ASHRAE Journal - April 2010 - 33
ASHRAE Journal - April 2010 - 34
ASHRAE Journal - April 2010 - 35
ASHRAE Journal - April 2010 - 36
ASHRAE Journal - April 2010 - 37
ASHRAE Journal - April 2010 - 38
ASHRAE Journal - April 2010 - 39
ASHRAE Journal - April 2010 - 40
ASHRAE Journal - April 2010 - 41
ASHRAE Journal - April 2010 - Technology Award Case Studies: Greening Hospitals
ASHRAE Journal - April 2010 - 43
ASHRAE Journal - April 2010 - 44
ASHRAE Journal - April 2010 - 45
ASHRAE Journal - April 2010 - 46
ASHRAE Journal - April 2010 - 47
ASHRAE Journal - April 2010 - 48
ASHRAE Journal - April 2010 - 49
ASHRAE Journal - April 2010 - Technology Award Case Studies: Sustainable Remedy for Hospital
ASHRAE Journal - April 2010 - 51
ASHRAE Journal - April 2010 - 52
ASHRAE Journal - April 2010 - 53
ASHRAE Journal - April 2010 - Building Sciences
ASHRAE Journal - April 2010 - 55
ASHRAE Journal - April 2010 - 56
ASHRAE Journal - April 2010 - AP1
ASHRAE Journal - April 2010 - AP2
ASHRAE Journal - April 2010 - AP3
ASHRAE Journal - April 2010 - AP4
ASHRAE Journal - April 2010 - 57
ASHRAE Journal - April 2010 - 58
ASHRAE Journal - April 2010 - 59
ASHRAE Journal - April 2010 - Emerging Technologies
ASHRAE Journal - April 2010 - 61
ASHRAE Journal - April 2010 - 62
ASHRAE Journal - April 2010 - 63
ASHRAE Journal - April 2010 - Technical Topics: Selecting Efficient Fans
ASHRAE Journal - April 2010 - 65
ASHRAE Journal - April 2010 - Technical Topics: Dual-Capacity Heat Pumps
ASHRAE Journal - April 2010 - 67
ASHRAE Journal - April 2010 - 68
ASHRAE Journal - April 2010 - 69
ASHRAE Journal - April 2010 - IAQ Applications
ASHRAE Journal - April 2010 - 71
ASHRAE Journal - April 2010 - 72
ASHRAE Journal - April 2010 - 73
ASHRAE Journal - April 2010 - International Column
ASHRAE Journal - April 2010 - 75
ASHRAE Journal - April 2010 - 76
ASHRAE Journal - April 2010 - 77
ASHRAE Journal - April 2010 - 78
ASHRAE Journal - April 2010 - 79
ASHRAE Journal - April 2010 - 80
ASHRAE Journal - April 2010 - 81
ASHRAE Journal - April 2010 - 82
ASHRAE Journal - April 2010 - 83
ASHRAE Journal - April 2010 - 84
ASHRAE Journal - April 2010 - 85
ASHRAE Journal - April 2010 - Classified Advertising
ASHRAE Journal - April 2010 - 87
ASHRAE Journal - April 2010 - Advertisers Index
ASHRAE Journal - April 2010 - Cover3
ASHRAE Journal - April 2010 - Cover4
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