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Specific market segments have gravitated towards unit designs because of their overall features, ease of installation, initial cost and system performance.
These are smaller pools with light usage compared institutional pools. Besides the pool water heating option, they tend to go without some of the other heat recovery options that are usually incorporated into larger units. This configuration is usually refrigeration based with the outdoor ventilation air connected directly to a special intake at the unit. The space heating coil is also mounted internally. The exhaust fan is usually installed in the space with its intake over the hot tub. They tend to be vertical units and installed in the pool filter room. The air conditioning heat rejection is to a remote outdoor air-cooled condenser.
The vertical configuration in Figure 14 is very popular in hotel and residential applications because of their compact footprint and 2-side service access. These PV and NV models are available with or without pool water heating. The maximum size is limited to 100 lb/h capacity.
There are a multitude of other configurations available should a horizontal unit or outdoor packaged system suit the project better. The heat rejection can also be to a geothermal loop, dry cooler or cooling tower.
This configuration has enhanced air quality control capabilities and also offers economizer operationl. These systems are designed with multiple dedicated duty exhaust fans. The first exhaust fan (EF1) is sized to maintain the room's negative pressure by exhausting 10% more room air than is introduced to the space as code mandated ventilation outdoor air. The second exhaust fan (EF2) sized to allow for full purge/evacuation of the space with a 100% outdoor air mode.
Figure 16 shows a unit in "Normal Operation" where EFI maintains the room's negative pressure. EFI can be unit mounted or remotely installed with its intake located above the whirlpool whenever appropriate. EF2 is normally off and operates only when a purge or economizer demand exists.
The outdoor air intake is set to introduce the code required ventilation outdoor air (aka Minimum OA) until the system goes into Purge or Economizer when it opens to 100.
These minimum outdoor air and EF1 airstreams at vastly different conditions present a perfect opportunity for heat recovery. Seresco provides unit mounted heat recovery between these two air streams using a glycol run-around loop. The coils just slip into the airstreams of this unit configuration. This approach to heat recovery offers the best performance and design flexibility while staying in the smallest possible cabinet. Figure 17 shows a unit in "Normal Operation" with the glycol heat recovery coils in place.
Adding the glycol run around loop heat recovery option to your Seresco unit in a northern installation will typically realize a one year payback on your investment!
If the system design has remote exhaust fans, the glycol run around loop can still be used for heat recovery. An significant added benefit to heat recovery is the tempering of the outdoor air before it can mix with the system air. Tempered outdoor air will not create condensation problems during the cold weather. In northern climates it is very common to add a separate heating coil for the outdoor air if heat recovery is not being used.
NOTE: Traditional supply & return fan configurations with a mixing box are not a good choice for a Natatorium application. There are three significant shortcomings compared to the Seresco method:
Figure 18 shows a unit in "Purge-Economizer mode". There are three significant benefits to this configuration:
These system features can be designed into the ductwork or incorporated into the unit as a complete package.
|Exhaust Fan Operating Sequence Example|
|Exhaust Fan - EF1||Exhaust Fan - EF2||Outdoor Air|
|Normal Operation||ON||OFF||Minimum required by code|
|Purge - Economizer Mode||ON||ON||100%|