Pressurized vs. Non-pressurized water heaters

[mrkino]

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

 

[PEDARRIN2]

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.

 

[EdStainless]

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.

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Plymouth Tube

 

[zdas04]

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

 

[mrkino]

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.

 

[dicksewerrat]

Is this potable water? contamination by exposure to the atmosphere

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com