Solar Energy Hot Water and Calculation

Solar Energy Hot Water and Calculation

A four story building located in Hammond Indiana has 100 rooms and is used as a dormitory for students. A sketch of the building is shown in Figure 1. There are 25 rooms per floor and each room is occupied by three students. The school operates for fall (15th of August to 15th of December), spring (15th of January to15th of May) summer (15th of May to 5th of August) semesters. Each room has a 3ft x 6ft window. The specifications for walls and windows are given below. The hot water load by month is determined and is shown in Table 1. The average hot water demand is 13.1 Gal/student per day. Due to the relatively large static head, approximately 50ft, and the freeze potential at the site, the conceptual system selected for this site should be a closed loop antifreeze system. Assume $40/ft2 for evacuated and $30/ ft2 for flat collector and an average of $20/ ft2 for installation for evacuated and flat collectors. The heating for each room is done by electric and 70ºF is preferred. The sun exposure schedule is given below.

a. Select the system, either flat plate or evacuated tube collector b. Select the dimensions for the collector c. Calculate the total collector size d. Calculate the storage size e. Select the flow rate and pump size f. Determine the energy required to maintain water load per month as shown in Table 1. g. Calculate the solar heat contribution through the widows per room for each month. h. Calculate the total kWh needed per year to heat each room. i. Assuming $0.1/kWh for electricity, calculate the total cost of heating per year. j. Investigate the installation of solar heating k. Calculate the total cost of such system, if 1000 BTU of heat from a solar panel cost $100. l. Calculate total cost m. Calculate the pay pack (simple pay back method 5% interest rate)

Figure 1.Building layout

Wall and Window Characteristics For the wall, the components 1 and 3 are 10cm brick and the center one is 5 cm stagnant air. The wall is plastered 25 mm on both sides. Wall outside resistance = 0.044 Plaster 25 mm = 0.025/1.39 = 0.018 Brick 10 cm = 0.10/.25 = 0.4 Stagnant Air 50 mm = 0.18 Brick 10 cm = 0.10/0.25 = 0.40 Plaster 25 mm = 0.025/1.39 = 0.018 Inside Surface Resistance = 0.12

Table 1 Hot water requirement per month

Month Gallons Cold Water Temp(ºF)

Hot Water Temp(ºF)

January 122,000 48 140 February 110,000 48 140 March 122,000 50 140 April 118,000 52 140 May 61,000 57 140 June 59,000 59 140 July 61,000 61 140 August 61,000 62 140 September 118,000 63 140 October 122,000 60 140 November 118,000 55 140 December 112,000 50 140

Date Sunrise Sunset Length Change Dawn Dusk Length Change

Today 07:18 17:49 10:31 06:49 18:17 11:28

+1 day 07:19 17:48 10:29 00:02 shorter 06:50 18:16 11:26 00:02 shorter

+1 week 06:26 16:40 10:14 00:17 shorter 05:57 17:09 11:12 00:16 shorter

+2 weeks 06:35 16:33 9:58 00:33 shorter 06:05 17:02 10:57 00:31 shorter

+1 month 06:54 16:22 9:28 01:03 shorter 06:23 16:53 10:30 00:58 shorter

+2 months 07:16 16:27 9:11 01:20 shorter 06:45 16:59 10:14 01:14 shorter

+3 months 07:07 16:59 9:52 00:39 shorter 06:37 17:29 10:52 00:36 shorter

+6 months 05:50 19:45 13:55 03:24 longer 05:20 20:15 14:55 03:27 longer Notes: Daylight saving time, * = Next day.

Darkness Dawn Sunshine Dusk Notes: How to read this graph? Change preferences.

Variable I II III IV V VI VII VIII IX X XI XII

Insolation, kWh/m²/day 1.73 2.56 3.61 4.60 5.38 6.00 6.04 5.25 4.29 2.94 1.77 1.50

Clearness, 0 - 1 0.46 0.48 0.49 0.49 0.49 0.52 0.54 0.53 0.53 0.49 0.42 0.44

Temperature, °C - - 2.10 8.72 14.81 19.82 21.84 20.56 16.53 10.58 3.96 -

6.19 3.60 3.36

Wind speed, m/s 6.76 6.49 6.72 6.72 6.01 5.60 5.20 5.04 5.46 6.09 6.42 6.43

Precipitation, mm 43 37 64 96 92 102 98 92 94 70 77 61

Wet days, d 11.7 9.9 12.6 12.6 10.8 9.8 9.6 9.2 9.2 9.2 11.0 12.4 These data were obtained from the NASA Langley Research Center Atmospheric Science Data Center; New et al. 2002

Hammond, Indiana, United States - Basic information Latitude: +41.58333 (41°34'59.988"N) Longitude: -87.5 (87°30'00"W) Time zone: UTC-6 hours Local time: 19:01:28 Country: Indiana, United States Continent: Americas Sub-region: Northern America Distance: ~3.8 km (from your IP) Altitude: ~180 m