General Description
Operation
Technical Specifications

General Description

The ITLL building ventilation system is a variable air volume (VAV) system. The VAV terminal units are responsible for supplying a sufficient air volume ( ;

) to the rooms they serve to maintain temperature and acceptable air quality.

This means that as the overall building air flow requirements increase or decrease, the main fans in the air handler speed up and slow down, to provide only as much air as is required. In addition, the terminal units responsible for controlling the air flow to each zone (room or area sharing a single thermostat) can control air flow with motorized dampers ( ;

).

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In the early morning, for example, when the building does not require much cooling, the main fans will run more slowly, reducing the total air flow through the system. However, even at this time, a VAV terminal box supplying a room with many occupants can fully open its damper, providing needed cooling. As classrooms begin to fill up during the day and the sun rises, generally heating the building, the total air flow will increase as necessary. If some rooms remain unoccupied throughout a particular day however, the VAV terminal boxes for those rooms will remain closed.

Although the initial cost of installing a VAV system is a somewhat higher than a traditional constant air volume (CAV) system; due in part to special controllers used to control the fan speeds and the added complexity of the VAV terminal boxes, the money saved when these big fans are running below maximum speed quickly pays off.

Each VAV terminal unit has a motorized damper which opens and closes, on command from the main control system, to allow more or less air flow. Sensors in units 41 and 42 measure air flow, damper position and supplied air temperature for monitoring by students studying the ventilation system.

In addition, hot water heating (reheat) coils and internal fans are installed in VAV units serving rooms with outside walls and windows, which sometimes require more heating than central rooms. If a particular room requires heating, but the supply air temperature [ ;

] is 55°F (12.7°C) or higher, the reheat coil reheats the air before it enters the room.

If the amount of fresh air in the main air supply is sufficient to meet the indoor air quality requirements, but the air flow past the reheat coil is too little to extract sufficient heat to warm the room, the internal fan in the VAV unit pulls in additional air from the room to increase the air flow past the coil.

Operation

The wall-mounted thermostat determines how much the supply air valve should open in order to maintain the room temperature. Occupancy mode (occupied / unoccupied) is pre-programmed in a user-adjustable 7-day and holiday schedule schedule.

Units with integral hot water heating coils

When the thermostat calls for heating, the Direct Digital Control (DDC) system closes the supply air valve to provide a minimum of outside air (to maintain indoor air quality) and opens the heating coil water control valve to maintain the room temperature.

In fan-powered units

During the occupied cycle, if the thermostat (;

) calls for cooling, the DDC system fully opens the supply air valve and turns on the fan

(

).

If the thermostat calls for heating, the DDC closes the supply air valve just to provide minimum ventilation air. If this does not increase the room temperature, the heating coil water control valve opens sufficiently to maintain the room temperature (

).

The fan will not run, and the heating water valve will not open if the supply air valve is not in its minimum position.

During the unoccupied cycle, the heating coil water control valve remains open and the DDC system controls the fan speed to maintain room temperature.

The DDC system allows the room occupants to override or enable the heating coil controls and the baseboard radiator controls for experimentation purposes.

Technical Specifications

Air Terminal Units (VAV Boxes)

Plan Symbol	VAV-41, 42
Submittal Ref. #	15930
Location	LVL 1, Rm 160
Manufacturer	Environmental Technologies
Supplier	Long & Assoc., 922-6660, Craig Mueller
Type	Parallel, Fan Powered
Model No.	DFVL