actuators on dampers

[Johan2]

Hi guys.

Could someone please explain to me what controls the actuators on the AHU. Their is dampers for fresh air and then you have got dampers on the return air side back to AHU. What sensor controls these dampers actuators.

Thanks :o

[Brian_UK]

They can respond to a 0 - 10v signal.

The main controller will be working on temperature or maybe enthalpy to maintain conditions in the downstream ductwork.

[frank]

Or on occupancy, or warm up.

During warm up, the fresh air input will be kept to a minimum, with full recirc position.

When up to temp, the dampers will modulate to allow more fresh air into the building, typically 25% minimum, and, during Summer, 100% fresh air input.

Basically, whatever has been programmed into the BMS controller, will dictate the position of the dampers.

[Tesla]

Hi Johan2
The sensor which usually controls these dampers is the OAT outside air temperature sensor and sometimes incorporate an outside air humidity sensor. So there are three control methods enthalpy, CO2 or temperature. CO2 sensors are relatively new and expensive, these are mounted in the return air flow to measure how much fresh air is required.
The BMS usually sends out one signal of 0 to 10 volts which goes to all three damper sets - Return Air, Outside Air and Spill/Relief Air. The actuators normally have a reversing switch or (if not) are mounted the opposite way on the shaft. This way a balanced flow is maintained.
There are several modes of operation - Early morning warm up, Night time free cooling/purge, Outside air cooling (ambient dependant) this is usually the first stage of cooling where chilled water is the second. The fres air modulation can be controlled by the actuator but there is usually two sets of dampers on the outside air where one is fixed (no actuator) to provide the minimum fresh air.

[PRESS]

Hi Johan2.

All the answers you have above there are great. I will try to further simplify things for you. You have a controller obvously which is controlling the functions of your AHU and in RSA this will commonly be Johnson FX Facility, Carel PO3, Innotech or some other brands like Landis and staefa or simmens. Your dampers will naturaly be controlled by this controller. The point is you will have an outside air temperature sensor which will tell the controller what temperature it is outside and your return air temperature which will tell the controller what temperature is the air returning from the building. One of the basic control philosophies encoporated by most designers is of utilising the two sources of return air for effective cooling and maximising on energy saving. Here is an example which suits some conditions in RSA:
1. On a typical winter day your outside air temperature is less than 18DegC so your controller will shut the return air dampers and make use of free cooling ( Economy Cycle )by opening fresh air dampers.
2. On a typical summer day your outside air temperature is above 18DegC so your controller will use air returning at a range of up to 23/24DegC for cooling the building.

The factors being utilised here is passing air at a resonably lower temperature already so as to reduce work done by the chillers. Obviously this comes with energy saving thereby reducing the carbon footprint of the building.

There are advanced applications on the air quality side of the same dampers eg as mensioned by Tesla above which monitor your co2 levels in the building by monitoring your return air co2 levels.

All what the dampers will get is a 0to10v signal from the controller so as to achieve what status it is required to be at any given moment.

I hope you will find this useful.

www.isentropictemptech.com (http://www.isentropictemptech.com)