We are putting together a baseline of a high rise residential building. In Appendix G, it states that we need to use 19 w/gpm. However, in the commentary, it states that this is based off of 60' of head and 60% pump efficiency pump. In the Proposed, we have a pump in excess of 125' of head. The fact that our design has such a high head is hurting our comparison with the baseline.
Is there any way to alter this 19 w/gpm to align it more closely with the function of the actual building? Can we increase that value to closer to 40 w/gpm, which is the reality due to the increase in head required?
Thank you all in advance.
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
September 9, 2013 - 1:50 am
what is your current w/gpm? This should improve with bigger equipment, not degrade.
Wes Lawson
Mechanical EngineerBala Consulting Engineers
4 thumbs up
September 9, 2013 - 5:29 pm
We are looking at about 40 w/gpm based on a 100+ HP pump. This is due to the size and height of the building. It is pushing our proposed building to have 3+times the pump energy of the base, due to the 60' assumption for the 19 w/gpm.
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
September 10, 2013 - 3:53 am
Waterloops (except drinking water) are usually closed loop systems, so the height of the building does not play a role, only the length and layout of the network with the pressure drop componants on it. I think your HP (heat pump?) does not use water, but is actually a VRF and uses refrigerant. The pump requirement that you refer to is for hot water and does not apply to refrigerant circuits.
I'm just guessing here, but my experience is saying that you are missing something.
Wes Lawson
Mechanical EngineerBala Consulting Engineers
4 thumbs up
September 10, 2013 - 6:45 am
We are not conveying refrigerant, we are conveying water. We have a heat pump system with an open cooling tower tied to the heat pump loop serving the building via heat exchangers, with boilers to inject heat, etc. We will have 2 sets of pumps. 1 set serving the tower loop and the other set serving the building loop. The compressors are in the heat pumps. There is no outdoor component to the heat pump, as it is not a split system.
Due to the network, and related extensive quantity of piping, we do have large pumps. These are 100+ ft head pumps, which is driving the w/gpm to about 40 w/gpm. Am I able to perform any adjustments to the baseline pumping system to more closely reflect out actual set of circumstances?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
September 10, 2013 - 9:26 am
I am assuming that you have a gas-fired boiler on your loop and are therefore modeling a system #1 in the Baseline.The baseline GPM is auto-sized and the pump energy must be 19 W/GPM according to G3.1.3.5. There are no adjustments or extra allowances I am aware of. The loops are very different and sometimes you pay a penalty in Appendix G comparisons relative to design choices. Hopefully you are making it up elsewhere.
Wes Lawson
Mechanical EngineerBala Consulting Engineers
4 thumbs up
September 10, 2013 - 9:28 am
Yes, we are using System 1 as the baseline. Thank you for the confirmation on the 19 w/gpm.
Wes Lawson
Mechanical EngineerBala Consulting Engineers
4 thumbs up
September 10, 2013 - 9:31 am
And we cannot put 19 w/gpm in the proposed either, right? We need the BHP? Have you had any success with the head as an input in lieu of the horsepower, or is that trying to find a loophole?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
September 10, 2013 - 9:43 am
The Proposed must be modeled as designed. The reviewer will check the pump power modeled and the pump power in the mechanical schedule for consistency.
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
September 10, 2013 - 10:00 am
I have not seen any interpretation or exception on this matter. That doesn't mean that there aren't any and you could check
https://www.ashrae.org/standards-research--technology/standards-interpre...
My gut feel is that it is the intent of these simulations to heighlight the pros and cons of system choices which should be wholelistically considered. Perhaps you have a fantastic COP, but the downside is water makeup and increased pumping power. What works for one building doesn't always work for another. A closed loop cooling tower may have been a better choice so that you don't need to battle the hydrostatic pressures of a highrise. I assume you have had a close look at the hydrolic simmulation to make sure the pipe sizing is as per local code requirements...these can be quite critical...you just need one badly sized componant on your worst leg of piping and it could scew the whole thing. Good luck.