Page 151 - Alternative Energy Systems in Building Design
P. 151

SOLAR POWER SYSTEM DEPLOYMENT    127


                         Prior to designing the solar power system, the designer must calculate the residential
                       power consumption demand load. Electrical power-consuming items in a household must
                       be calculated according to the NEC-recommended procedure outlined in the following
                                                          2
                       steps. The calculation is based on a 2000-ft conventional single-residential unit:
                         Step 1: Lighting load. Multiply the living space square area by 3 W: 2000 × 3 =
                         6000 W.

                         Step 2: Laundry load. Multiply 1500 W for each set of laundry appliances, which
                         consist of a clothes washer and a dryer: 1500 × 1 = 1500 W.

                         Step 3: Small-appliance load. Multiply kitchen appliance loads rated 1500 W by 2:
                         1500 × 2 =× 3000 W.

                         Step 4: Total lighting load. Total the sum of the loads calculated in steps 1–3: 6000
                         + 1500 + 3000 = 10,500 W.
                         Step 5: Lighting load derating. Use the first 3000 W of the summed-up load (step 4),
                         and add 35 percent of the balance to it: 3000 + 2625 = 5625 W.
                         Step 6: Appliance loads. Assign the following load values (in watts) to kitchen
                         appliances:


                           ■ Dishwasher                  1200

                           ■ Microwave oven              1200
                           ■ Refrigerator                1000
                           ■ Kitchen hood                 400

                           ■ Sink garbage disposer        800
                           ■ Total kitchen appliance load  4600

                         If the number of appliances equals five or more, then the total load must be multi-
                         plied by 75 percent, which in this case is 3450 W.

                         Step 7: Miscellaneous loads. Loads that are not subject to power discounts include
                         air-conditioning, Jacuzzi, pool, and sauna and must be totaled as per the equipment
                         nameplate power ratings. In this example we will assume that the residence is
                         equipped with a single five-tone packaged air-conditioning system rated at 17,000 W.

                       When totaling the highlighted load, the total energy consumption equals

                          17,000 (air conditioner) + 3450 (appliances) + 5625 (lighting power) = 26075 W

                       At a 240-V entrance service, this represents about 100 A of load. However, considering
                       the average power usage, the realistic mean operating energy required discounts full-time
   146   147   148   149   150   151   152   153   154   155   156