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It is extremely important to select the correct size of the solar water heater system. The solar water heater sizing needs to be done based on the hot water requirements and the hot water use habits of the people in a family. The basic idea of having a solar water heater is to reduce electricity consumption for water heating. An under-sized system is insufficient to meet the hot water requirement, an over sized system will result in overheating of the water. As back-up system is required for cloudy days, it may be possible to manage with marginal back up use in extreme weather to optimize the size of the system for use in the rest of the year.
Selection of solar water heater system in large residential, commercial and industrial applications is complex in nature and therefore elaborate calculations may be necessary to size the solar water heater system. However following guidelines can be used fairly accurately for small residential applications and to get a general idea about the size of the solar water heater systems for large residential and commercial installations.
| Water consumption pattern in small commercial establishments, at 40 degree centigrade. | |
|---|---|
| Water consumption in beauty saloon | |
| Shaving per person | 0.5 |
| Hair rinsing per person | 05 |
| Water consumption in small clinic / dispensary | |
| Hot water per patient | 05 |
| Water consumption in small hospitals (30 beds or less) | |
| Hot water per patient | 60 |
| Water consumption in restaurants / Canteens | |
| Hot water per guest | 05 |
| Water consumption in small office | |
| Hot water requirement per employee | 02 |
| Water consumption in Hostels | |
| Hot water requirement per student | 40 |
| Water consumption in large hospitals (more than 30 beds) | |
| Hot water requirement per bed | 300 |
| Water consumption in large hotels | |
| Hot water requirement per room | 300-600 |
| Water consumption pattern for residential applications at 40 degree centigrade | |
|---|---|
| Water consumption pattern in high end bungalows in cities Liters | |
| Bathing per person per day | 80 |
| Wash basin per person per day | 20 |
| Kitchen wash per person per day | 15 |
| Clothes wash per person per day | 10 |
| Heat loss and hot water wastage factor | 30% |
| Water consumption pattern in high end residential flats in cities | |
| Bathing per person per day | 60 |
| Wash basin per person per day | 10 |
| Kitchen wash per person per day | 15 |
| Clothes wash per person per day | 10 |
| Heat loss and hot water wastage factor | 25% |
| Water consumption pattern in average residential flats in cities | |
| Bathing per person per day | 40 |
| Wash basin per person per day | 10 |
| Kitchen wash per person per day | 15 |
| Clothes wash per person per day | 00 |
| Heat loss and hot water wastage factor | 20% |
| Water consumption pattern in semi urban households | |
| Bathing per person per day | 40 |
| Wash basin per person per day | 10 |
| Kitchen wash per person per day | 00 |
| Clothes wash per person per day | 00 |
| Heat loss and hot water wastage factor | 20% |
| Water consumption pattern in rural households | |
| Bathing per person per day | 40 |
| Wash basin per person per day | 00 |
| Kitchen wash per person per day | 00 |
| Clothes wash per person per day | 00 |
| Heat loss and hot water wastage factor | 15% |
| SL No. | Description | Water/person/day | No of persons | Total water requirement |
|---|---|---|---|---|
| 1 | Bathing | 40 | 4 | 160 |
| 2 | Wash basin | 10 | 4 | 40 |
| 3 | Kitchen wash | 15 | 4 | 60 |
| 4 | Clothes wash | 0 | 4 | 0 |
| 5 | Total requirement | 260 |
| SL No. | Description | %loss of total requirement | Total water requirement |
|---|---|---|---|
| 06 | Heat loss and hot water wastage factor | 20 | 52 |
| 07 | Total hot water requirement of 40° C | 312 |
Hot water is required mainly in the winter season and therefore the system should be designed to meet the hot water requirement during winter. Table 7 gives the hot water output of a typical 100 liter system at 60º C and the output varies from place to place depending upon environmental conditions.
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