Domestic hot water is the second consumer of energy in our homes, 26% of total energy consumption. Currently, in newly built homes, it is mandatory to cover part of the energy consumption needed to produce the hot water through a solar thermal system and, if that could not be done, use another type of renewable energy. Even so, the demand for energy to produce hot water remains high.
We want to give you some ideas of what systems exist and which are the best according to the solar climatic zone where the building is located, the number of people who live in the house and their customs regarding water.
The Most Common Systems
When deciding whether an tankless hot water system or tank is better for a home, it must be borne in mind that, although the power needed to generate it instantaneously must be higher than that installed with an accumulation system, the fuel consumption. It does not have to be superior, but the opposite since the accumulation systems must maintain water at a certain temperature inside the tanks (accumulators) and this will generate losses through isolation.
Hence, the accumulators must have good insulation so that these losses are as small as possible. However, those systems with accumulation provide greater comfort to the user, by the ability to offer higher peak flow.
Tankless Systems
These are systems that heat water at the same time it is demanded. This is the case of the usual gas or electric heaters, or wall heating and hot water boilers (mixed boilers). The main advantage: it is not necessary to keep the hot water accumulated, which avoids a higher energy cost.
Instantaneous systems generally have limited features when it comes to supplying hot water at two points at a time, but they are still the most common systems. In this way, this type of system is the most appropriate for families that are not numerous, in homes with few inhabitants or in those where their use is very punctual.
Gas vs Electric Water Heaters
There are two types of tankless water heaters: electric and gas units. Both of them have their advantages and disadvantages. Here are some of the differences between Gas and Electric water heaters to help you make the right choice.
Pros of electric tankless water heaters:
- Great choice of models
- Convenient for periodic use
- Require less space
Cons of electric tankless water heaters:
- Long-term cost is far higher compared to gas units
- Less productive
According to this post, the best producers of electric tankless water heaters are:
- Stiebel
- EcoSmart
- Rheem
Pros of gas tankless water heaters:
- Energy efficiency
- Faster heating
Cons of gas tankless water heaters:
- Risk a gas leak
- More expensive units
The best producers of gas tankless water heaters are:
- Rinnai
- Takagi
- Noritz
The Accumulation Systems
This type of systems can be divided into two:
- Those that are composed of a device that heats water (a boiler or a heat pump, for example) plus a thermo-accumulator
- Electric resistance thermo-accumulators
The compounds by boiler and accumulator are the most used. Once heated, the water is stored in an insulated tank so it can be used at any time.
It avoids the continuous on and off of the boiler, since it works continuously; allows hot water to be used simultaneously at two different points; being a centralized system, less power is needed to bring hot water to the set of users; they are easily combinable with the solar collection systems (sanitary hot water), and that allow access to cheaper fuel tariffs. Experts recommend this system when it is known in advance that the consumption of hot water can be continuous.
On the other hand, electric resistance thermoaccumulators are a not very recommendable system from the energy and cost point of view. When the temperature of the water contained in the thermos drops below a specific temperature, an auxiliary resistance usually starts to operate. Hence the importance of the thermos, in addition to being well insulated, connects only when necessary, through a timer.
Other Systems
As an alternative to the two most used systems is mixed type: they combine a certain hot water accumulation for use throughout the day, but they also have an instantaneous production system. These hybrids between heater and boiler have a lower capacity tank, and their prices vary according to the capacity and capacity of the deposit. We can find mixed atmospheric gas boilers that work with natural gas, boilers and vertical boilers and bithermal gas mixed boilers, which work with butane or propane.
Hot Water Temperature
Taking into account that the hot water production system can be mixed instantaneously or by accumulation, we can establish two temperature sections:
With accumulation (the temperature must be high to get enough production of hot water) the recommended is between 131ºF and 140ºF but then consumed at 104ºF. The use of thermostatic taps is recommended.
When the production of sanitary hot water is instantaneously mixed, the temperature should be between 86ºF and 95ºF. It is because when the temperature is 2 or 3 degrees higher than the desired one, we do not have to mix with cold water. The boiler will use less power to heat the water -which reduces the energy expenditure; lengthens the life of the boiler reducing calcifications of components.
