In buildings intended for people to work and live in, a necessary technical system, apart from heating, cooling, ventilation and air conditioning, is also a system for preparation of sanitary hot water. Depending on the purpose of the building is different and needs for the consumption of hot water, which affects the choice of the system itself. Demand for hot water consumption varies depending on the purpose of a particular building, affecting the choice of the system. The general classification of these systems, similar to heating and air conditioning systems, is the classification into local and central systems. Other classifications can be made, depending on the method of production, into flow (tankless) and accumulation (with storage tanks) systems, in addition, depending on the type of heaters, in systems with electric, hot water or steam heaters and finally, depending on a thermal energy source, they can be either systems that use conventional fuels or system based on renewable energy sources.
Heating domestic hot water can be performed by using local (decentralized) or central systems. Decentralized domestic water heating is used for individual consumers, for example, for a single outlet, where due to lower water consumption and consequently lower heat output requirements for its heating, continuous flow electric water heaters can be used. If there is a group of consumers, either flow gas water heaters or electric water boilers, could be used. Local systems for sanitary hot water production are often applied in residential buildings with a smaller number of housing units.
2.1. Sanitary hot water heat pumps
Heat pumps, as an unconventional source of heat, can also be used for sanitary water heating. Using them, we can expect heating costs savings, considering that compressor heat pumps use thermal energy which comes from the environment, and along with the appropriate expenditure of mechanical work, a suitable heating temperature is obtained (using the heat that comes from condensation of refrigerant fluid in the heat pump).The performances can be various, and therefore, the condenser of the heat pump can be installed in the very sanitary hot water boiler (water storage tank), in the shape of a tubular heater, or the sanitary water from the boiler can circulate via the pump through the condenser of the heat pump.
2.2. Solar Domestic Hot Water systems (SDHW)
Solar systems can generally be divided into active and passive.
Passive solar systems Passive solar systems do not use any additional devices or elements that would spend the extra energy for operating the system. These are mainly different architectural solutions, aimed at better collection of solar energy, its accumulation and use for heating. The key component of the system is a solar energy receiver, which is commonly called “a solar collector”.
According to its construction, the receiver can be:
Active solar systems
For our climatic conditions, solar systems are almost ideal solutions for sanitary hot water preparation. As far as heating systems are concerned, it is very difficult to make a solar system that can compensate for heat losses throughout the heating season without any additional heat source. There is also a variant that involves solar collectors coupled with heat pumps, where a little higher temperature of heat transfer fluid can be obtained, but in that case, an additional heat source is needed – during the periods of very small intensity of solar radiation and very low outdoor air temperatures.