×
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!
  • Students Click Here

*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.

Students Click Here

Jobs

Radiant Heat - Why Boiler Loop and Primary Loop?

Radiant Heat - Why Boiler Loop and Primary Loop?

Radiant Heat - Why Boiler Loop and Primary Loop?

(OP)
I saw a system the other day with 4 "stages" of pumping.  There was a non-condensing "boiler loop" with a pump that fed a "primary loop."  The "primary loop" had a pump that just circulated around in about a 15' perimeter.  Pulling off of that were injection pumps that dumped into a "secondary loop".  The "secondary loop" contained the manifolds and all the individual zone pumps.  So, there were 4 different "stages" of pumping.  I understand that the injection pump process is to inject small amounts of very hot water into the lower temp radiant loops while at the same time not allowing the boiler return water temp to get too low.  And I understand the zone pumps.  What puzzles me is why was there a "primary loop" seperate from the "boiler loop".  Since the injection pump system is designed to protect the boiler, it would seem that the "boiler loop" and the "primary loop" could be one in the same.  Any idea why they should be seperate; it just adds a pump to the system?

RE: Radiant Heat - Why Boiler Loop and Primary Loop?

It may be that over the years modification have been performed and that each engineer of each project chose to play it safe by adding a pump and secondary loop for their system to make sure the primary system do not run out of gpm. Nowadays with better control, two way valves and VFD pumps you can eliminate other pumps and secondary loops. Just make sure you also design a bypass for minimum flow.

RE: Radiant Heat - Why Boiler Loop and Primary Loop?

If it was a non-condensing boiler, then the primary/secondary setup insures that the boiler always sees a high return water temperature (above 160F), while the secondary circuits mix down to the required secondary loop temperatures.  Radiant heating systems where the floor is used as an emitter want to be operating at surface temps of less than 90F, so that means water temps in the 95F to 115F range depending on the type of radiant system.  

RE: Radiant Heat - Why Boiler Loop and Primary Loop?

GMcD you are not supposed to design secondary systems as you said. The return of each loop should be equal to the the boiler design entering water temperature. It is the supply temperature to each loop that is varied.

RE: Radiant Heat - Why Boiler Loop and Primary Loop?

This thing sounds like it had 3 primaries plus the zone loops?

Most gas fired non condensing boilers will handle down to 140F return water temp.  Oil fired is higher.  The system sounds like a Joe Bob abortion to me.  I'm sure it works... but it sounds like it has a lot of unnecessary complication and pumping and thus failure points.

Jabba

RE: Radiant Heat - Why Boiler Loop and Primary Loop?

Lilliput1 - Not sure how you read that into my post.  Absolutely the returns from the secondary circuits have to be matched to the boiler return water temp.  A good source of further flavours of boiler circuit set-ups is John Siegenthaler's "Modern Hydronics".  Lost of good info there.

RE: Radiant Heat - Why Boiler Loop and Primary Loop?

There is no need for the boiler loop separate from the primary loop, but I saw a system that was somewhat similar because it was designed for addition of solar panels in the future; the panels would dump heat into the primary loop whenever available, and if that wasn't enough the boiler would kick in.

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