INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Economizer damper control in heating season

Economizer damper control in heating season

(OP)
Hello All,

ASHRAE 90.1 recommends supply air temmperature to control the economizer dampers and cooling coil valve. The standard provides clear reasoning for doing it.

My question is related to heating season. From your experience ,did anyone had any issues with coil freezing if similar approach is used in heating season. i.e. SAT controls economizer damper and heating valve. Heating valve only comes ON when dampers at minimum OA position. Is there any reason you would recommend any changes in the below sequence?

SAT controls the outside air damper, preheating coil, and heating coil
- Free cooling mode - Economizers controls SAT
- Heating - Outside damper will be at minimum position and preheat coil valve will open first to maintain SAT. Once preheat valve is 90%,heating valve will start opening to maintain SAT.
- Low mixed temperature limit can be separate control loop. i.e when MAT falls below 6 degree C, preheat valve opens to maintain MAT to 10C.

Thanks


RE: Economizer damper control in heating season

What is the order of coils in the AHU? Is the HW coil first or the CW coil first in OA?

RE: Economizer damper control in heating season

(OP)
The sequence is outdoor air damper, pre-heat coil, heating coil, & cooling coil. Thanks

RE: Economizer damper control in heating season

Coil arrangement should be preheat coil, cooling coil then reheat coil if the AHU serve only one space. If multiple spaces are use each should have variable air volume box & terminal reheat coil. If heating coil is upstream of the cooling coil, the cooling coil will be heated up. The heating coil should be controlled to maintain space heating temperature, not supply air temperature. The preheat coil should be controlled in sequence with the OA damper closing to minimum position to heat the air downstream of the preheat coil to 50F.

RE: Economizer damper control in heating season

Yes, preheat coils can freeze when water flow is too low, it is therefore not customary to modulate flow of preheat coils.

However, I believe your description of heating sequence is not complete. Preheat coils should not open befor heat coils in all scenarios, but only when the outdoor temperature falls bellow trigger point, on higher outdoor temperature heat coil should modulate alone.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close