The disparity lies in the size of water passages within the heat exchangers. Plate-and-frame heat exchangers feature significantly smaller passages compared to their shell-and-tube counterparts. The larger passages in shell-and-tube units not only facilitate water to flow through the unit more freely, but also mitigate concerns regarding the accumulation of deposits, considering pool water contains elements such as calcium and additives.
In practice, it is a common sight to encounter large steel shell-and-tube heat exchangers with cupronickel tube bundles when servicing existing equipment at pool complexes or water parks. Many existing heating systems are sized to raise the water temperature from startup conditions, assuming the entire body of water is at the utility supply temperature. Sizing for the startup load means the system will be oversized for the vast majority of time the system is in operation. There exists room for improvement.
There are three primary areas where pool owners stand to benefit from a modified heat exchanger system.
- Reducing the overall heat exchanger capacity
To achieve an immediate reduction in energy consumption when updating the heat exchanger design of a facility, the most effective approach is to size the heat exchangers according to the actual operating load rather than startup conditions. Typically, large pool heating systems are initially sized to accommodate peak load conditions, which should ideally occur only once throughout the pool’s entire lifespan, typically when it is new. Otherwise, the body of water is extremely unlikely to be completely drained and refilled, as the facility’s highest heat demand takes place at this point. Maintaining the desired temperature thereafter requires considerably lower heating input.
Sizing the heat exchangers to match the maintenance load, opposed to the startup load, results in a reduction in initial costs, energy consumption, and maintenance expenses. When tasked with replacing heat exchangers, a determination is made regarding the extent to which the system’s heat transfer capacity can be reduced. This involves calculating the input required to sustain the desired temperature while considering factors such as the ambient air temperature, incoming water temperature, and the speed at which the customer wishes to attain the setpoint temperature following backwashes, among other considerations.
It is important to note that while this approach may lengthen the time required to reach the setpoint temperature during initial startup, this becomes inconsequential when the facility is already in operation. As long as the pool reaches the desired temperature overnight following a backwash, downsizing the heat exchangers carries no drawbacks.
