7/28/2019 268_pdfsam_2.3- Mechanical, HVAC & Plumbing Specification Novotel

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Gulf House EngineeringJanuary 2010

07-C106 NOVOTEL AL DANA RESORT TOWERS PAGE 266 SECTION 15850 AIR HANDLING UNITS

AHU- Selector (H-O-A) switches position.AHU Healthy status.

If both are positive, BMS DDC controller will give an opencommand to AHU fresh air intake damper to open its minimumposition for preset level. After a time delay it will give a startcommand to AHU supply air fan VFD.

G. Humidity (Option)

Fresh air and Return Air humidity and temperature is monitored byBMS DDC Controller through humidity sensors and the same willbe used to calculate inside and outside Enthalpy. The difference ininside and outside Enthalpy will initiate free cooling operation of AHU.

H. Temperature Control

In the common areas AHU supply return and fresh airtemperatures will be continuously measured by the duct mountedtemperature sensor; which is installed in AHU supply air, return airand fresh air duct respectively.

The temperature difference between the supply and the supplyair temperature set point value will generate the coolingdemand. The control loop within the controller will perform themathematical calculations and compare the measured valueand current set point value. If the measured value is morethen the set point value, cooling loop will be initiated. Thevoltage level from sensor is converted into a number, whichthe sensor will scale into degree centigrade. The loop will thengenerate a proportional control output designed to reduce theerror to the actuator fitted on the 2- way modulation valve andchilled water is allowed to enter the Coil.

The above action results in the cooling and dehumidificationprocess, thereby reducing the dry- bulb temperature and themoisture content of the air entering the room. The cooling isachieved by removing the sensible/ latent heat from the air.

If the supply air temperature is lower than the set point thecontrol loop shall modulate the valve up to 0% for less

cooling and thereby reducing the level of reduction in thedry bulb temperature.

I. CO2 or Fresh Air Quantity Control/ Indoor Air Quality

In the common areas AHU CO2 concentration level will bemeasured by CO2 sensor installed in critical place wherepresumed more occupancy. (The concentration level ranges of 400to 1200PPM or 700PPM above outdoor air). The BMS DDCcontroller will compare the measured value of CO2 concentration

and set value. If the measured value is higher then the set value,DDC controller will generate the proportional control output to thefresh damper to open more and return air damper to close more so