×
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

Pressurized vs. Non-pressurized water heaters

Pressurized vs. Non-pressurized water heaters

Pressurized vs. Non-pressurized water heaters

(OP)
Working on a hot water dispenser.  What's some pros and cons for pressurized vs non-pressurized tanks?  Most water heaters are pressurized and I'm trying to see if non-pressurized tanks are at a disadvantage in terms of flow performance.  The inlet pressure let's say is 20 psi  

RE: Pressurized vs. Non-pressurized water heaters

If you are talking about a plumbing hot water dispenser, then all hot water tanks are pressurized, i.e, there is not vent to atmosphere on the water storage.  

But,  not all water heaters are ASME rated tanks, though.  For a hot water dispenser, you can likely go with a non ASME rated tank.

RE: Pressurized vs. Non-pressurized water heaters

I believe that it a matter of pressure limits and control.  After all without them being pressurized there wouldn't be any flow.
For low flow rates a low pressure is suitable.  It is often easier to regulate the pressure of the inlet water rather than making sure that you control the maximum pressure of the hot water.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Pressurized vs. Non-pressurized water heaters

Pressurizing the vessel has some significant thermodynamic benefits.  The space above the water is always at 100% relative humidity.  The actual mass of water vapor that is represented by 100% RH varies widely with changes in temperature and pressure.  At zero psig it is over twice the evaporation rate at 20 psig, and since a vented application will always be exchanging warm air for cooler air the evaporation can be a significant portion of your water consumption and your energy load.  In a pressurized application, the amount of water in the void space is significantly less and there is no exchange with cooler air.  Depending on your application a pressurized unit can be significantly less expensive to operate.

David

RE: Pressurized vs. Non-pressurized water heaters

(OP)
Thanks for the response people and I also meant to say FLOW and THERMODYNAMIC advantages.

Well lets just say I have close to a gallon holding tank that's an open system.  Would 100% Relative humidity even be significant with such a small volume to affect power consumption.  The reason I'm asking is I wanted to stray away from the purge vent valve of a closed system and just have the tank open to atmosphere and also move away from a pressure vessel tank.  Since it is going to be directed to the drain, I wouldn't have to worry about water expansion and it would just leak to the drain.

RE: Pressurized vs. Non-pressurized water heaters

Is this potable water? contamination by exposure to the atmosphere

Richard A. Cornelius, P.E.
WWW.amlinereast.com

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