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Optimised water temperature gives lower energy consumption and higher performance

Caroline Jacobsson

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By optimising the inlet water temperature in a waterborne climate system, a number of benefits can be achieved. For example, it is possible to save up to 15% of the energy consumption, in addition you get increased comfort and increased performance of the people in the building.

The benefits of a waterborne climate system are many. Water can carry almost 3500 times as much energy compared to the corresponding volume of air. This means that the height of the HVAC installation is often significantly lower compared to an airborne climate system, and that the amount of insulation around ventilation ducts is reduced.

With a waterborne climate system it is often sufficient with a smaller size of the air handling unit as you do not have to boost the air flow in the same way as with an airborne climate system. Most of the temperature demand can be handled via the water side while the air side ensures good air quality. In this way, the air temperature can be kept relatively high, which also means that the size of the cooling machine can be reduced.

With a smartly designed water system it is possible to use the needs of different zones in an energy-efficient way. E.g. use the return temperature from the south/southwest zone of an office building as supply water to the northern part of the building.
A waterborne climate system is therefore a very energy-efficient choice! One way to save additional energy is to optimise the inlet water temperature.

Let’s look at an example
Normal water temperatures in comfort module systems are 14/17 C°. The days during the year when the building's temperature requirements are less than designed temperatures, energy can be saved by optimising the water temperature against the rooms' actual needs. Instead of working with the temperatures 14/17 C°, the real needs of the zones can be measured and the water temperatures raised to for example 16/18 C°, which can save as much as up to 15% of the energy consumption. Calculations show that for each degree that the cooling water temperature is raised, 3% of cooling energy is saved. For each degree of heating temperature is lowered, 2.5% of heating energy is saved.

Except from saving energy there are several other benefits of optimising the inlet water temperature. It is possible to avoid oversizing of cooling and heating production units. Simulations show that buildings normally only needs full power from the climate system 10 days a year, the rest of the time it is possible to use less capacity and hence a smaller production unit.

By optimising the inlet water temperature, the risk of condensation is also reduced. When the humidity is high the risk of condensation is high, normally the cooling valves close when approaching the dew point. If the cooling water temperatures are increased condensation can be avoided, the cooling valve can stay open and supply cooling to the room and thus keep the room temperature down - both energy efficient and with comfort in focus.

Another benefit with optimising the water temperature - in both cooling and heating mode - is that by lowering the delta T the mixing between room and supplied air volume becomes more efficient. Thus the risk of cold draught and high velocity of air in the occupied zone is reduced, which increase the comfort. By increasing the comfort the performance of the people who are in the building increases, since comfort and performance are strongly linked to each other. (Read more here)

There are several advantages with optimising the inlet water temperature in a waterborne climate system. The people who use the building get better comfort, increased performance while at the same time saving energy.