Updating Equipment Load Factors for the ASHRAE Handbook

From eSociety, December 2018

Plug loads are one of the main contributors to the building’s overall energy consumption in most office buildings, so they need to be considered in load calculations, according to an article in the latest Science and Technology for the Built Environment.

Weekday and weekend power consumption profiles are developed for different office equipment in the article, “Equipment Power Consumption And Load Factor Profiles For Buildings’ Energy Simulation (ASHRAE 1742-RP),” written by Omer Sarfraz, Student Member ASHRAE, and Christian Bach, Ph.D., Associate Member/Student Branch Advisor, an assistant professor at Oklahoma State University who is also the webmaster for ASHRAE TC 8.4, Air-to-Refrigerant Heat Transfer Equipment.

Load factor profiles are developed for some typical office spaces and are compared against the peak load factors listed in the 2017 ASHRAE Handbook—Fundamentals, and recommendations for the minimum number of testing days necessary to obtain the equipment peak heat gain are included.

Sarfraz and Bach explain the significance, challenges and purpose of their research.

What is the significance of this research?

This research provides an update on equipment load factors for the ASHRAE Handbook. These load factors are part of building load calculations, which allow for accurate determination of HVAC equipment size. In addition, it provides average weekday and weekend power consumption profiles for commonly used office equipment for building energy simulations.

Why is it important to explore this topic now?

Plug loads are one of the main contributors to overall modern building power consumption. They consume up to 50% of the total electricity consumption of buildings with high efficiency HVAC systems (New Buildings Institute 2012). Plug load power consumption profiles were last updated by Abushakra et al. (2004).

Since then, use of mobile devices and laptop docking stations has increased, but was not adequately considered in the ASHRAE Handbook. This research fills that gap and furthermore provides updated power consumption profiles for various office equipment.

Also, this research determined a minimum number of testing days to obtain office equipment peak heat gains, filling another gap in open literature.

References:
Claridge, D.E., B. Abushakra, J. Haberl, and A. Sreshthaputra, 2004. “Electricity Diversity Profiles For Energy Simulation Of Office Buildings.” ASHRAE Transactions 110(1), 365–377.

New Buildings Institute. 2012.” Plug Load Best Practice Guide—Managing Your Office Equipment Plug Load.” Portland, OR: New Buildings Institute.

What lessons, facts and/or guidance can an engineer working in the field take away from this research?

This research provides power consumption profiles for commonly used equipment for both the weekdays and weekends separately. For load calculation purposes, use of average peak gains in ASHRAE Fundamentals (2017) for different equipment as an input to building energy simulations can result in overestimation of the office/building load.

It is recommended to use weekday and weekend power consumption profiles for equipment presented in this research as an input to building energy simulations rather than relying on the peak heat gains.

How can this research further the industry's knowledge on this topic?

The primary goal of this research was to update the load factors in the Handbook. However, it also showed that there is a large number of equipment that may be not traditionally considered in load calculations, such as thermal food processing equipment, dorm refrigerators in individual offices, as well as newer personal electronic devices.

The mix and count of the devices has substantial impact on the thermal loads, is a function of the space use, and should be considered during the HVAC design as closely as possible to reduce the risk of over- or under-sizing of equipment.

Were there any surprises or unforeseen challenges for you when preparing this research?

During the literature review, no recommendation or guidelines on minimum number of testing days to obtain office equipment peak heat gain or load factors for standard ASHRAE offices were found in literature. Hence, equipment power consumption data was recorded for extended period of time to ensure that peak heat gains were adequately captured.

Finding test site volunteers proved difficult and was only possible due to the generous help of numerous volunteer supporters. Additionally, it proved difficult to obtain data for some specialized equipment, such as cash registers, due to concerns about potential damage by the UL listed data loggers to the equipment.

ASHRAE members have free online access to Science and Technology for the Built Environment using their existing ASHRAE member login information.

Science and Technology for the Built Environment, ASHRAE's archival research publication, offers comprehensive reporting of original research in science and technology related to the stationary and mobile built environment.