Variable primary chilled h2o loop
Variable primary chilled h2o loop
(OP)
Hey guys, I am new to the site and I am NOT a mechanical engineer (hopefully I am not violating any rules) but I would like to become one eventually. I currently work for a large HVAC mfgr. on the service end. Let me start by saying that hydronics are not my strong suit. I came upon a chilled water system today that was having some flow issues. Upon inspection I found that the make up water and expansion tank were on the discharge side of the pump. The PRV has a tag on it that says set at 30# and the relief valve is set to open at 50#. The discharge pressure at the pump was 36# @60 Hz. The suction pressure was 0 or in a negative (gauge does not read neg. pressure). Shouldnt the make up be on the suction/low pressure side of the system to ensure the loop is always full? If anyone has any links to online information or training classes/videos regarding hydronics, I would love to check it out. Im sure im leaving a lot of information out but hopefully I can get a few responses. Thanks in advance..
-Dan
-Dan





RE: Variable primary chilled h2o loop
Apparently hydronics also wasn't a strong suit for the guy who designed that system.
Get this book if you ant to become a mechanical engineer. Expensive but worth it.
RE: Variable primary chilled h2o loop
To answer your specific question, read:
http://documentlibrary.xylemappliedwater.com/wp-co...
Hydronic heaven!
knowledge is power
RE: Variable primary chilled h2o loop
http://www.jmpco.com/page.cfm?sp=schematic&app...
RE: Variable primary chilled h2o loop
RE: Variable primary chilled h2o loop
Expansion tanks should be located at the point where the system is to
be stabilized, not necessarily at the suction of the pumping system.
With the advent of variable-speed pumps and their digital control, the
operation of a pump is not dependent on its suction pressure being
constant. In the past, the expansion tank was always located at the
pump suction and took its air from the air separator. This expansion
tank was of the plain type without an internal bladder that separates
the air from the water. The result was absorption of air by the water
and waterlogging of the tank.
This nuisance was eliminated by the bladder-type expansion tank.
This expansion tank is located away from the air separator, and this
enables the designer to locate the expansion tank at the desired point
of pressure regulation in the water system, not just at the point of
installation of the air removal equipment.
On low-rise buildings, the expansion tank for both hot and chilled
water systems can be located at the suction of the pumps. On high-
rise buildings, the expansion tank and water makeup equipment
should be located at the top of the building to ensure continuous pres-
sure at that point in the system.
from Rishel, J. B., Durkin, T. H., & Kincaid, B. L. (2006). HVAC pump handbook. New York: McGraw-HiIl.
So there's no need to keep the expansion tank at the pump suction and it should be kept at the top? I don't understand. Can someone clarify please?
RE: Variable primary chilled h2o loop
RE: Variable primary chilled h2o loop
VFD didn't change anything for location of expansion tank, at least i don't see how. whne a VFD throttles the pump, all it does is make the large pump be a small pump from a pump performance point.
the fact that we no use bladder tanks also doesn't have anything to do with the pressures. At least I don't see why this woudl matter.
RE: Variable primary chilled h2o loop
RE: Variable primary chilled h2o loop
Examples of closed water systems in a building would be both the chilled water and hot
water systems that deliver water to the various heat transfer equipment that functions to
provide conditioned air and heat to the building. These systems always contain an
expansion tank, which can be either an open expansion tank or a closed expansion tank.
The open expansion tank is always at the highest point of the particular system and is
open to atmosphere, but the area of the water in the tank is insignificant to the point that
it does not alter the definition of a closed water system as one that is not exposed to
atmosphere.
So the type of the expansion tank matters.
Also the reference you kindly provided advises to install the system pump or pumps to pump away from the point of no pressure change so that the pressure differential produced by the pump will at every point in the system always increase the operating pressure above that of the non-operating pressure.
When I compare this advise to the advise from the ASHRAE guide above and the one from the handbook in my last point I find it confusing.
RE: Variable primary chilled h2o loop
take it this way, it is better to connect tank on the pump inlet side but if you connect it on the pump outlet side, it will not be a disaster, it still work fine.
you can read ASHRAE handbook, it advise to install it on inlet side but did not prevent installation on the outlet side.
RE: Variable primary chilled h2o loop
http://www.taylor-engineering.com/downloads/articl...