International Project
Each RTPU is also equipped with a Microtech Unit Controller and a BACnet communication interface . The rooftop units are mounted on matching 914mm ( 36 inch ) high flat roof curbs .
The RTPUs do not have humidification devices . 1
1 and 2 :
One of the Daikin rooftop units .
2
Medium pressure supply and return ductwork is routed from the RTPU on the roof to a riser shaft where the ducting will drop down vertically in shafts and then branches off to main duct runs on every floor to serve single duct Variable Air Volume air terminals ( VAV ‘ boxes ’). The VAV boxes are designed to have minimal pressure drop and low noise levels . The onboard controller of each VAV box controls the airflow rate of conditioned air into an occupied space in response to a thermostat control signal .
The incorporation of a multipoint crossflow airflow sensor allows the VAV box to compensate instantly for any change in supply air pressure that might alter the supply volume resulting in a pressure independent variable air volume system . Electrical reheat coils in the VAV box are factory mounted and ETL listed to meet electrical safety standards including complying with CSA 236 / UL . The electric heaters are a side-mounted and slide-in style , specifically designed to mount in the extended terminal casing allowing for easy field maintenance . To ensure safe operation , these electric heaters use thermal safety switches and low watt density heating elements to minimise hot spots . The control damper features a double gasket .
Galvanised steel medium pressure ductwork is constructed to a static pressure class of 1000Pa ( 4 ” water gauge ). The ductwork from the VAV ‘ boxes ’ are low pressure galvanised steel ductwork constructed to a static pressure class of 250Pa ( 1 ” water gauge ). All supply and return ductwork are externally insulated and constructed in accordance with Sheet Metal and Air Conditioning Contractors ' National Association ( SMACNA ) Standards for appropriate pressure class .
Variable Air Volume Terminal ( VAV Boxes ).
Various exhaust fans are installed on the roof . One exhaust fan is installed for the air extraction of the core toilets and janitor rooms , while four exhaust fans are provided for the extraction of the tenant areas . Each fan is connected to a variable frequency drive / variable speed drive . The type of exhaust fans used are centrifugal vent set fans with bolted and continuously welded steel construction , electrostatic baked polyester powder coating , fan housing with access door and drain , flat blade fan wheel , OSHA belt guard and weather cover , extended lube lines , inlet flex duct connection , steel isolation rails and spring isolators , nonfused disconnect switch .
Toilet and general exhaust system . Observe the non-return dampers which is a code requirement .
Independent DX split systems are provided for the lift ( elevator ) machine room and the outdoor units are positioned on the roof .
Unitary DX units serve elevator control room , electrical and server rooms .
During summer months when ambient temperature may reach more than 40 ° C ( 104 ° F ) it is vitally important to ensure optimal air circulation over the air-cooled condenser coils in the rooftop
48
RACA Journal I February 2022 www . hvacronline . co . za