[Equest-users] Unmet Load Hours - VAV with no re-heat

Shruti shrutiak at gmail.com
Fri May 4 08:55:10 PDT 2012


Dana, 
Did you make sure that the central gratin coils are actually operating when you remove reheat? Sometimes you have to input  the hot deck max leaving temperature for the central and reheat coils to turn on.

Sent from my iPhone

On ४ मे २०१२, at ८-४५ म.पू., Dana Etherington <Dana.Etherington at crbusa.com> wrote:

> Thanks for the input guys.
>  
> So this is actually a new construction project and we’re performing the modeling for LEED certification. Rob, I originally entered process equipment electrical usage as eq. w/sf to the space and varied sensible heat gain % to the space based on what was reasonable. The corresponding process hot water and chilled water loads are accounted for via a detailed schedule and load the respective circulation loops. I’m hesitant to add internal energy sources, I feel like I’d be double-dipping..
>  
> The units themselves are VAV and I do not believe there are individual VAV boxes at the zone level. So I just ran the model with VAV and included the re-heat coils, keeping everything else exactly the same as with the multi-zone model.
>  
> Results for VAV with re-heat, compared to MZS with no re-heat: overall energy cost for the year increased by only .2% and unmet load hours were slightly higher (applied a uniform re-heat delta T). Not sure which would be more acceptable by LEED reviewers…
>  
> -Dana
>  
> From: Rob Hudson [mailto:rdh4176 at gmail.com] 
> Sent: Friday, May 04, 2012 11:23 AM
> To: R B; Dana Etherington; equest-users at lists.onebuilding.org
> Subject: Re: [Equest-users] Unmet Load Hours - VAV with no re-heat
>  
> If you have heavy heating loads in the space, then should try to replicate that by putting in a heat load in the internal energy tab of the spaces.  This will force the higher return temperatures and make it unnecessary to have re-heat coils.  
>  
> This may work for you, because it seems like in reality, the spaces don't require the reheat coils and the spaces are kept to temperature.
>  
> Hope this is helpful,
>  
> Rob
> 
> On Fri, May 4, 2012 at 11:00 AM, R B <slv3sat at gmail.com> wrote:
> I am assuming this is an existing building. I have always had this issue. I do all the stuff that you have and use the reheat also, if the unmet hours are too many.  I also look at the SS-F report to see how low the temps are and when (hourly report) - if they are acceptable, then I leave the reheat out. You could also widen the throttling range - there might be unmet hours in the actual building - people just don't complain if it is a few degrees less/more than the thermostat. You should look at the hourly report to see if the heating coil is coming on (these reports are not very clean - since it is not clear for what point in the air stream eQuest is reporting the temps). Do you have VAV boxes - sometimes I have seen that a constant volume system has a VFD added to the fan, without VAV boxes in the space. You could reduce the min flows to zero and see if that helps. I haven't dug deeper into it, but I think the VAV system is going to set the supply temps low when even one zone needs cooling/less heating and so others will need reheat. If things are working smoothly in the existing building, then the zones must be similar and may not need too much variation in supply temps for different zones. I haven't used MZ - but that would probably work - what is the difference in energy consumption between the two options? I have not been comfortable with the economizer and MZ together.
>  
> I will be curious to know what you find.
> -Rohini
> 
> On Fri, May 4, 2012 at 8:48 AM, Dana Etherington <Dana.Etherington at crbusa.com> wrote:
> Hi folks,
>  
> We are modeling a large facility operating with multiple VAV AHUs with central heating and cooling coils, but no re-heat at the zones. There are high heat loads in the spaces and therefore higher return air temperatures than the norm.
>  
> When I remove the re-heat from the systems I have excessive unmet load hours (heating). I have specified “HEAT-SET-T” to activate the central heating coil. I also have cooling control set to “warmest” and heat control set to “coldest”. If I do not set the coil capacity it is still not meeting the loads. The only way I have been able to eliminate these unmet hours is by adding the re-heat back in or changing it to a multi-zone (MZS) system with all the same parameters.
>  
> If I model this scenario using the multi-zone system in eQuest to get around this would that be vastly different than VAV with no re-heat? Has anyone had this issue before? Any insight is appreciated. Thanks!
>  
> -Dana
>  
> Mr. Dana Etherington, E.I.T., LEED AP BD+C | CRB | One Kendall Square Ste B2202 | Cambridge, MA 02139
> Main: 617-475-3050 | Direct: 617-475-3061 | Mobile: 617-583-3009 | Fax: 617-475-3052 | Ext: 6061
> Email: dana.etherington at crbusa.com | www.crbusa.com
> ________________________________________________________________________________________
>  
> This document may contain confidential information and is intended for use by the addressee only. If you are not
> the intended recipient, please do not transmit, copy, disclose, or utilize this communication in any manner. If you
> received this message in error, please notify the sender immediately and delete this message.
>  
> ü Please consider the environment before printing this email.
>  
>  
>  
> _______________________________________________
> Equest-users mailing list
> http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
> To unsubscribe from this mailing list send  a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG
> 
> 
> 
> _______________________________________________
> Equest-users mailing list
> http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
> To unsubscribe from this mailing list send  a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG
> 
> 
> 
>  
> -- 
> Rob Hudson
> _______________________________________________
> Equest-users mailing list
> http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
> To unsubscribe from this mailing list send  a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20120504/af4de930/attachment-0002.htm>


More information about the Equest-users mailing list