Choosing the Optimum Domestic Hot Water Tank by DevexDevex Systems
Devex Systems specialises in the design and installation of state-of-the-art Hydronic Underfloor Heating systems. Hydronic Underfloor Heating is a closed system made out of pipes usually embedded in the slab, in which hot water runs through to heat the floor. Because it is a complete, separate system on its own (with a heat source), we often get requests from customer on how to integrate this system with a DHW system. One of the best solution to achieve this is actually to use a single heat source for both systems as well as a single-coil DHW tank as a heat exchanger between the closed, hydronic floor heating system and the open, DHW system. Not only does it make your system more simple (avoiding having two heat sources to maintain), but it can also reduce upfront and running costs.
When it comes to choosing a domestic hot water tank, size matters. With the wide range of offers available on the market, it is prudent to choose a properly sized domestic hot water (DHW) tank that will provide the right amount of hot water to meet the particular consumption needs of your household.
The type of heat source is one of several significant parameters to observe in sizing a DHW tank. With that said, users should be informed that DHW tanks are more efficient for use with boilers than with heat pumps. The latter setup typically results in a maximum temperature of 60°C. On the other hand, a typical boiler delivers a maximum temperature of around 80°C. The boiler, therefore, allows users to store 200 litres of 80°C water — certainly more energy than the 200 litres of 60°C water with heat pumps.
Another selection criterion is the power of the heat source. There is not much promise in purchasing a big DHW tank if the heat source does not provide enough power to heat it up when needed. The user must properly quantify the power of the heat source to help define the maximum capacity of the tank. Generally, it takes 1 hour to heat up 25 litres of water with 1 kilowatt. Proportionally, it would take 10 hours to heat up 250 litres of water with the same amount of energy.
In addition, the demand of hot water will help determine the minimum capacity for a DWH tank. The tank must not be too small to the point of running short of hot water to address the daily consumption demand. A standard economical shower head uses 9 litres of 45°C water per minute, equating to 4 litres of 80°C water per minute or 6 litres of 60°C water per minute.