Domestic hot water (DHW)
The domestic hot water (DHW) is water for human consumption (drinking) that has been heated. It is used for sanitary purposes (toilets, showers, etc.) and other uses of cleaning (scouring dishes, washing machine, dishwasher, scrubbing floors).
Use of solar thermal energy to obtain domestic hot water
One possible form of obtaining hot water is using the Sun through a solar thermal installation prepared for this purpose.
Obtaining hot water is one of the most used applications of solar thermal energy. It is also called "water hands."
Solar energy aspects to consider when installing a solar domestic hot water
Solar radiation received at a place is determined by the angle of the sun relative to the ground. In summer the sun is more perpendicular to the ground than in winter, so in summer we get more sunlight.
The energy required to heat water to a predetermined temperature is determined by the water temperature before heating. Therefore, in winter the water coming from the network is generally colder so we need more energy than in summer.
Solar hot water installations require a water tank so that when the water warms goes to store in a well-insulated tank for when you go to use. This is essentially due to two reasons: firstly the difference in solar radiation received during different times of the day, not to mention the null solar radiation that is received during the night and, secondly, because we will not use the hot water constantly. That is, most of the day but we do not need hot water but when we would be going to get a shower we would need warm much water in no time.
Economically we can not pretend sizing a system for obtaining all the hot water we need throughout the year because as we should oversize a lot to get a lot of heat energy in winter, this energy left over us in the summer, which cause the water storage tank will boil, it will generate steam and the pressure of this steam could bursting the tank.
One solution would throw hot water and then add cold water but it would be unreasonable economically and environmentally.
There are many regulations in different countries where it is required that the solar thermal energy for producing domestic hot water should be dimensioned for a reasonable consumption in summer and have an alternative system to overheat it when the system can not reach the temperature desired water.
Solar domestic hot water installations
There are two types of facilities (or heaters)
- Open circuit installations. Drinking water passes directly through the solar collectors. This system reduces costs and is more efficient (energetically), but presents problems in areas with temperatures below the freezing point of water, and in areas with high concentrations of salts just clogging the pipes of the panels.
- Closed circuit installations. Two systems differ: thermosiphon flow and forced flow.
Solar thermal panels have a very low environmental impact.
Last review: August 25, 2015