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Long-Term Commercial GSHP Performance, Part 5--Comfort and Satisfaction

©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 12, December 2012.

By Steve Kavanaugh, Ph.D., Fellow ASHRAE and Josh Kavanaugh, Student Member ASHRAE

About the Authors
Steve Kavanaugh, Ph.D., is a professor emeritus of mechanical engineering and Josh Kavanaugh is a post-graduate student in the mechanical engineering department at the University of Alabama, Tuscaloosa, Ala.

This article is the fifth in a series summarizing a data collection and analysis project to identify common characteristics of successful ground source heat pump (GSHP) systems. This article presents results from occupant satisfaction surveys.
GSHP building occupants were provided forms shown in Figure 1 that allowed them to rate their level of satisfaction. Five check boxes from “Very Dissatisfied” (= 1) to “Very Satisfied” (= 5) are selected, and results were used to achieve a numerical rating for seven areas of satisfaction. The wording for the check boxes attempts to be consistent with the terminology of ASHRAE Standards 55-2010 (…80% occupant acceptability…based on…dissatisfaction criteria…) and 62.1-2010 (…80% or more of people exposed do not express dissatisfaction.). A figure of merit of 2.8 is used to approximate 80% occupant acceptability, and 20% dissatisfaction (since “acceptable” responses are assigned a value of 3.0).

As shown in the figure, the satisfaction topics included room cooling comfort, heating temperature, indoor air quality (IAQ), lighting, acoustics, maintenance responsiveness, and ability to control temperature. Responses from 24 of the sites that had more than five responses and ENERGY STAR rating information were considered. The average number of respondents per site was 19, and they provided many insightful comments that mentioned specific reasons for dissatisfaction. A number of positive comments were also given. Sidebars to this article list comments from three buildings that received the highest overall satisfaction ratings and three buildings that received the lowest ratings.

Average occupant ratings in all areas except the ability to control were between acceptable and satisfied. Satisfaction level improved with increasing ENERGY STAR rating except in the areas of acoustics and lighting. There was a trend toward lower satisfaction, in some cases a marked decline, in all areas with newer GSHP systems. There was a higher level of satisfaction with occupant adjustable thermostats compared to GSHPs controlled by energy management systems that were often perceived to be non-occupant adjustable.


Occupant Satisfaction Results

Figure 2 plots occupant satisfaction level by comparing summer and winter indoor air comfort conditions to the ENERGY STAR rating. There is a slight upward trend with higher ENERGY STAR ratings, but the average ratings are only slightly above acceptable. There is much less scatter for sites with lower ratings and a sizeable amount of variation of satisfaction for sites with ENERGY STAR ratings above 80.

Four sites with high ENERGY STAR ratings had satisfaction levels below 2.8 for both heating and cooling comfort. Three of these four sites had ventilation air equipment capacities of 76, 66, and 41 cfm/person (36, 31, and 19 L/s per person) and all were controlled by energy management systems (EMSs). The fourth low rated site used a dual capacity heat pump with a damper system to serve two classrooms. The site also was served by an EMS.

Another low satisfaction site, controlled by an EMS, had a low cooling mode rating, but occupants commented the room temperatures were too cold rather than too warm. A low satisfaction site controlled by thermostats had a low heating mode comfort rating. Occupant comments indicated that the lights were turned off so students could see classroom “smart boards,” which disabled the heat pumps.

Figure 3 is a plot of the occupant satisfaction level with IAQ, lighting, and acoustics relative to ENERGY STAR rating. The average satisfaction ratings for IAQ are only slightly above acceptable, but the trend line shows a slight improvement with a higher ENERGY STAR rating. Four sites received a rating less than 2.8 and all were controlled by an EMS. The EMS at the one site that also had a low ENERGY STAR rating was programmed to disable the ventilation air system when the outdoor temperature was above 85 °F (29 °C) or below 40 °F (4 °C). This was related to a GSHP performance deficiency because the ground loop was installed at 113 ft/ton (10 m/kW). The sites with ventilation air equipment capacities of 76, 66, 56, 53, and 41 cfm/person (36, 31, 26, 25 and 19 L/s per person) had IAQ satisfaction levels of 3.3, 3.3, 3.5, 2.6 and 2.7 for an average of 3.1. This is slightly lower than the average IAQ satisfaction level for the other sites that had much lower ventilation air equipment capacities.

The average satisfaction rating for lighting was near 4.0 (satisfied) with a slight downward trend with higher ENERGY STAR rating. This trend is likely a result of lower Standard 90.1-2010 mandated lighting power densities for newer installations. Only two sites received ratings below 3.0. Both were equipped with “smart boards” that were difficult to view with the lights (and heat pumps) off.

Citation: ASHRAE Journal, vol. 54, no. 12, December 2012


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