Pool Dehumidification Systems, Desiccant or Hot-Gas-Bypass reheat?

by / Tuesday, 20 June 2017 / Published in Energy Auditing

I have recently been involved in a pool dehumidification project to size and select a new dehumidification unit for a pool in the Toronto area.

It was a small indoor pool, around 1000 SFT in size, used by tenants for recreational purposes. The Pool house was built above ground with lots of glass walls and a 200 SFT skylight on the roof.

Through performing a natatorium HVAC sizing, it was determined that a mechanical dehumidification system with nominal airflow rate of 6000 CFM total and 2000 CFM of outside air for ventilation would meet the ASHRAE requirements.

For this application two systems were considered, firstly, a refrigerant-based dehumidifier with heat reclaim, a hot gas bypass reheat coil and a desiccant wheel type dehumidifier. The Pool water heating and heat reclaim features were determined not to be cost effective and were not included in this project.

The second option was a desiccant dehumidifier that came with two 4 ton compressors which were half the size of the compressors for the refrigerant-based unit. However, the supply fan was larger to overcome the additional pressure drop through the desiccant wheel and a 3 HP regeneration fan was added to the system to dry-up the wheel. As a result, the total energy consumption of the two units was almost the same. Any savings on compressor operation was offset by the additional fans electrical consumption.

When the additional care and servicing required to maintain the desiccant wheel performance and the eventual cost of replacing the wheel, (the cost of which is considerable) the better choice is to use the conventional refrigerant-based style of natatorium dehumidification unit.  This cost-benefit analysis was largely completed based on an 8,760-hour energy consumption calculation and serves to confirm, at least in this specific application, the common thought in the industry that a mechanical, refrigerant-based dehumidification system is the best solution for natatoria.  Notwithstanding the calculation result, it was felt that the best approach was to specify the preferred unit and allow for alternative products to be accepted, which would ultimately reveal the true first costs of the relative systems.

Furthermore, every application is different and the results specific to your building should be considered as they are very sensitive to the operating parameters of pool size, water temperature, air temperature, pool deck size, occupant load, and construction materials for the building.

Amir Rahmani, P.Eng.

Amir has extensive experience in design and modeling of HVAC systems in buildings and has been the mechanical engineer for over 40 building retrofit projects and several new building constructions.

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