ASHRAE Journal - December 2009 - 59

ASHRAELine 2 is the cost of operating equipment, utilities and supplies required for each type of building, again on a yearly square foot basis. Note that costs range from 23 cents for a college building to $19.80 for a typical hospital—a spread of 8700 percent! Line 3 shows the installed cost of a quality year-round air-conditioning system, amortized over 20 yr at 5 percent, with 1 percent set aside for taxes. This figure includes regular maintenance of the system. Line 4 is the cost of an air-recovery system, again on an annual square foot basis, amortized over 20 yr at 5 percent, with 1 percent for taxes and 1 percent for insurance. While exact cost will vary with the volume of air required, in no cases should it go over these generous estimates. Line 5, operating costs of an airrecovery system, depends on the type of building and the number of hours the system will be in operation each day. Figuring power, cleaning labor, hot water, adhesives, parts, maintenance and the hours of operation (ranging from 1665 annually for a school to 8760 for a hospital), costs range from just over half a cent to nearly 2 cents on an annual square foot basis. Line 6, owning and operating. costs (found by adding lines 4 and 5), are also on an annual square foot basis. Again, these costs are liberal estimates and in practice engineers will find costs for specific buildings are lower. 59–2009 YE A R S JOURNAL F i g .2 How variable costs are reduced when the air is cleaned (BOMA). Cleaning and Decorating Expenses Line 7 shows typical cleaning and decorating costs on an annual square December 2009 foot basis, taken from experience ex-change reports from the Building Owners and Managers Association. Note they range from about 30 cents for a factory to over 3 times this much for a hospital. Line 8 shows the comparatively small percentage required to offset the cost of an air-recovery system. This was computed by dividing line 6 by line 7. Because line 6 is on the high side, actual percentages required will be less than shown. The largest single cost in operating a building is maintenance, and of maintenance expense, the most money is paid out for plain housekeeping—dusting, porter services, periodic redecorating. Here is where an airrecovery system can repay its initial costs over and over. No matter how clean the air, some basic cleaning costs (Fig. 2, from Building Owners and Managers Association) cannot be eliminated, such as sweeping, dusting, porter services. In an office, for example, a liberal cost estimate for these services is about 32 cents a square foot annually. The remainder (22 cents) spent for other cleaning and redecorating costs—washing windows and walls, cleaning lights, dusting high areas— can be reduced by using an air-recovery system. Absenteeism To figure what absenteeism costs in a typical building, the first step is to compute wages and salaries for the building types on an annual square foot basis (line 9). Salary costs range ASHRAE Journal 59

ASHRAE Journal - December 2009

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