Baseline gas use data for the Minneapolis multifamily housing stock has the potential to provide a benchmark for measuring future conservation, a basis for improved audit calculations of the savings and payback for various retrofit measures, and a context within which to interpret and apply the results of our multifamily retrofit field tests. Since no adequate baseline data was already available, our office selected and studied a sample of buildings with funding and technical assistance from Minnegasco.
Our sample consists of 19 buildings with more than one gas account from an initial random sample of over 450 multifamily buildings. Though biased somewhat toward larger buildings, it nevertheless spans a range from 10 to 67 apartment units and is fairly typical in terms of age, types of heating systems, and average numbers of occupants. Subsamples of five to twelve buildings for each end use of interest are smaller than preferred but still adequate to provide useful preliminary data on use for space heating, hot water heating, cooking stoves, and clothes dryers.
The largest end use in this part of the country is naturally space heating, and for the 12 available cases it required from 8,000 to 47,000 ccf/year of weather normalized use. Space heating use is strongly correlated with building size, so the most useful summary measure is that these buildings use an average of about 63,000 Btu/ft'/year. Use was somewhat lower for hot water systems than for steam systems, averaging 52,500 and 66,400 Btu/ft' /year respectively. Reference temperatures (the outside temperatures below which the buildings needed heating) averaged about 60.5 degrees, which is essentially the same as we have seen in Minneapolis single family homes.
The second largest end use is normally for domestic hot water heating. Only five buildings had accounts dedicated solely to this end use, and their consumption averaged about 174 ccf/year per unit. Hot water heating is also second to space heating in terms of seasonality, with about a two to one difference between winter use and midsummer use due to differences in use patterns with the seasons and especially to differences in the temperature of incoming water delivered by our surface water supply system. This degree of seasonality means that for audit calculations summer use on a combined space heating and DHW account should be multiplied by about 15 instead of 12 to estimate total annual DHW use.
The third largest end use is for cooking stoves. We had 103 usable stove accounts in eight different buildings, which averaged about 45 to 50 ccf/year per unit. This end use shows a weakly seasonal pattern with a winter peak, but more striking was the pronounced variation between buildings (building averages ranged from 33.4 to 74.0 ccf/year per unit). This variation was largely due to different household sizes in these buildings, with some anecdotal evidence for different use habits as well. There was no indication in this sample that stoves were being used commonly or substantially for supplementary space heating.
The smallest end use for which we had a useful sample was clothes dryer use. The eight buildings available for this analysis average about 8 ccf/year per unit. Results in the literature suggest that dryer use is also seasonal, but we saw only a weak indication of this. The average use we observed is well below other reported values, which we think may relate to different use patterns for shared laundry rooms than for the individual unit dryers studied in other reports.
Consumption for all non-heating end uses averaged about 232 ccf/year per unit, which is roughly half what we calculate to be typical in single family homes. This difference is presumably the combined result of the factors discussed for each of the component uses, including smaller households, more efficient systems, and different use habits.
Total use values were available for all 19 buildings, and they ranged from 6,700 to 58,000 ccf/year. Normalized for area the average use was about 80,000 Btu/ft'/year, with steam buildings significantly higher than hot water buildings (86,300 versus 70,200 Btu/ft/year, p<.02). The present results are about 20,000 Btu/ftL/year less than in our preliminary baseline study of buildings audited through 1984, and we believe that this difference is due to self-selection of early audit cases from among higher use buildings. The average breakdown of total use among the various end uses is roughly 72% for space heating (compared to 65% in single family homes), 20% for hot water heating, 6% for stove use, and 1% for clothes dryers.
Full Report (PDF)
Multifamily Baseline Study. Part 2: Gas End Use Characterization