In Greece, when we want to provide hot water for use with a heat pump, we usually install a common DHW tank with a coil heat exchanger, just as we did until now when we used oil boilers.

It is the most common and familiar solution. But the least efficient, when a heat pump is already in the equation. On the one hand, because heat pumps heat the water more slowly than the oil and gas boilers, on the other hand, because they traditionally operate at lower temperatures, with the result that the classic coil in common boilers is small and cannot deliver the thermal energy to the Water tank properly, thus creating problems with the heat pump and delay in heating up the tank.

A small improvement on the above is the use of a “hot water tank for heat pump”, as it is called by the companies that manufacture boilers in recent years, which has a larger coil so that the heat output at the water tank is better.

But we still do not use the heat pump efficiently in terms of hot water production. The surface of the coil inside the boilers has a limited ability to pass the thermal power from the heat pump to the water in the boiler, causing it to run unnecessarily long to heat the water. So, while the heat pump has a good efficiency, in the end we lose this good efficiency by making it run for a long time while also having a long waiting time for the shower.

The ultimate solution for hot water is the use of the integral hydronic tank (indoor module), designed by the heat pump manufacturers and combines the heat pump with the water tank perfectly. What does perfectly mean? It means factory tests and settings for 100% ability to deliver all the thermal power of the heat pump to the tank, so fast heating, so the heat pump runs as little time as possible and we have a short waiting time to get into the shower.

The heat pumps of the Swedish House CTC have the special Ecozenith555 heat tank and the EMMETI heat pumps have the special Eco Hydro Kit heat tank.

In addition, these water heaters combine many other advantages beyond the correct and fast heating of domestic water, as they have a multitude of components that are necessary in any heat pump installation and whose installation is almost always a headache both for finding the right place to install as well as for the correct way of placing them.

EMMETI’s Eco Hydro Kit has as standard equipment a three-way diverting valve, air vent, safety valve, two back-up electric heaters for heating and hot water respectively, by-pass valve, anode, two expansion tanks for heating and DHW and a 25-liter buffer tank for heating, i.e. all the equipment that is required anyway.

Similarly, CTC’s EcoZenith555 has a stratification tray that separates the tank into two parts so it can maintain separate top and bottom temperatures, a lower one for heating and a higher one for hot water, to maximize heat pump’s efficiency. It also has two electric back-up heaters, a four-way mixing valve for water suction from three points in the container and a compensated heating temperature setting. The Ecozenith555 is fresh domestic hot water technology, i.e. it stores heating water, which heats the domestic hot water instantly as this flows through two parallel arranged finned coils before it’s lead to the consumptions. In this way, the growth of legionella is avoided, and we never run out of hot water, since the heating tank is charged directly without the intervention of a coil.

The domestic hot water is sufficient for 7 bathrooms in a large house. The higher cost of these special tanks of CTC and EMMETI in relation to traditional tanks is compensated by the absence of material and installation costs of all the other aforementioned components of the installation. And we also avoid the risk of poor workmanship of the human factor in setting up all the individual components of the engine room

Antonis Paskalis, Mechanical Engineer MSc, AUTh, Technical Director at Thermovent Hellas S.A.