©2018 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 60, no. 2, February 2018.
By Douglas Reindl, Ph.D., P.E., Fellow ASHRAE; Marc Claas; Jake Denison
Douglas Reindl, Ph.D., P.E., is professor and director of the Industrial Refrigeration Consortium (IRC) at the University of Wisconsin-Madison. Marc Claas is a researcher at the Industrial Refrigeration Consortium. Jake Denison is a product development engineer with Evapco.
Although net zero energy buildings have been successfully demonstrated at residential and small to moderate commercial building scales, they have not been demonstrated for more energy-intensive operations such as food production or large refrigerated storage facilities. The reason is simple: residential and low-rise commercial buildings have the benefit of considerably lower energy use intensity (i.e., annual electric energy required per unit area of the building) when compared to a refrigerated facility.
Figure 1 shows the comparative energy use intensity of various facility types including: a food production facility with refrigerated storage, a health-care facility, a large cold storage warehouse, a commercial office building, and a single-family residential dwelling. The high energy use intensity of a food production facility significantly increases the degree of difficulty and costs for achieving net zero energy performance. One factor that increases the degree of difficulty in implementing sufficient renewable energy production on-site is the large area required to deploy sufficient renewable energy generation to power a food process or refrigerated storage facility. This area is significantly larger than the facility footprint that might use rooftop photovoltaic solar alone.
The analysis presented in this article will show the magnitude of land area required to power such a facility. We also quantify the costs for deploying sufficient renewable energy generation to achieve net zero performance; however, land costs are not included in the economic analysis due to the significant variation in prices based on location.
Refrigerated Facility Overview
The analysis presented in this article is based on an actual refrigerated warehouse comprised of two separate refrigerated docks, a cooler, and three freezers totaling 166,875 ft2 (15 500 m2) of conditioned space. The size and respective temperature setpoints for each of the refrigerated spaces in the facility are given in Table 1, and the actual metered electrical energy demand and consumption for the facility are used in the analysis that follows. The electrical energy use intensity of this facility is 157 kBtu/ft2·yr (1,783 MJ/m2·yr) and it compares well with the “Large Cold Storage Area” energy use intensity shown in Figure 1.
In this article, we define a “net zero facility” as one that would be capable of producing at least as much electric energy on-site from renewable sources as it consumes over an annual operating cycle. More specifically, the on-site renewable energy production is sized to annually produce electrical energy equal to the facility electric energy consumption. We assume the facility is grid-connected and the electric utility provides necessary electric power whenever the site electrical demand exceeds the on-site renewable electricity production. We also assume the utility accepts any surplus on-site electricity production during periods when the facility electric demand is less than the renewable energy production. The only constraint applied is that the renewable electric energy production equals the facilities’ annual electric energy consumption.
Figure 1
Table 1
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