Page 32 - Climate Control News magazine February 2023

Indoor Air Quality
BENEFITS OF DEDICATED OUTDOOR AIR DEHUMIDIFICATION
Generally maintaining surface humidity below 60%rh will maintain a neutral mould and bacterial growth rate. Humidity induced problems can occur in building design practices that ignore the substantial “part load” hours when little cooling is required but humidity is still considerable.
BETTER TEMPERATURE
& RH CONTROL
The effect of a preconditioned desiccant can dry the fresh air to below 5Cdp. This is neutralised by having desiccants.
REDUCED AIR CONDITIONING COIL WORK
The design practice of DOAS with desiccants is now widespread and the use of Exhaust
Air in and Energy Recovery Ventilator ERV option also reduces energy use.
REHEAT AVOIDANCE
Reheating of overcooled air is a traditional low cost practice to allow the air- conditioning plant to dehumidify to dewpoint (ie 12°C) and re-heat the air back towards room temperature.
INCREASE COP
DOAS allows the used of chilled beams and smaller more efficient plant.
How to use DST
modelling method
INCREASED VENTILATION TO improve Indoor Air Quality (IAQ) is often in conflict with the challenge of energy reduction.
A comparison of ventilation technologies is often analysed at peak design, as it is difficult to model all relevant climatic scenarios and com- mercially available modelling is not available. The DST Modelling Method has evolved due to the need for makeup air modelling and the emergence of Dedicated Outside air System (DOAS) technology.
To support this, we detail the psychometrics of conventional baseline HVAC compared with five alternate technologies: Energy recovery ventilators (ERV), Desiccant DX, with Chilled water module (CHW) and ERV options. Weather Data sourced from ASHREA are modelled with Visual Basic (VB).
These methods can then be ranked on suita- bility bases on peak demand, operating cost, and ventilation cooling performance require- ments of various cases. We demonstrate a manual calculation method of three prominent technologies, being Baseline with ERV’s
LEFT: Dedicated Outside Air System (DOAS) installation.
BELOW: DST Dryer technology.
(passive desiccant) and Desiccant DX package. The options are compared with the capital cost to model financial expectations of ventilation in various Australian climates.
All DOAS systems provide viable energy results as long as there is a humidity control expectation. Typically OA needs to consider internal latent loads which needs to be 3g/kg below setpoint (i2 Room 21C 60%rh 9.3g/kg, OA needed for 7.5l/s per person is 6.1g/kg or 7Cdp, without this overcool and reheat requirement occurs.
DST Dryer manager, Gordon Lacey, has worked with Desiccant design since 1986 and developed a VB version in 2010.
He has provided substantial energy savings for over 200 supermarkets, libraries, clean- rooms, hospitals, hotels and a range of other humidity related applications.
Solutions for Pressure, Temperature, Air Quality, Flow and Thermal Energy Monitoring
WET/WET DIFFERENTIAL PRESSURE TRANSMITTER SERIES 629HLP
ROOM PRESSURE MONITOR SERIES RPME
MAGNESENSE® DIFFERENTIAL PRESSURE TRANSMITTER SERIES MSX
DIFFERENTIAL PRESSURE SWITCH SERIES ADPS
INSERTION THERMAL ENERGY METER SERIES IEFB
CARBON DIOXIDE/ TEMPERATURE TRANSMITTER SERIES CDT
+61 (0) 2 4272 2055 I dwyer-inst.com.au
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