[Equest-users] Does eQuest properly account for latent loads in infiltration & ventilation?

[Bruce Easterbrook]

I would think without the ability to heat or reheat you aren't 
controlling your humidity to 50% RH in the New Orleans building.
Bruce Easterbrook P.Eng
Abode Engineering

On 13/03/2013 04:42 PM, Z Smith wrote:
>
> In eQuest, we were using the '24 hours high use" setting building 
> operation schedule, which is that the building is always occupied---so 
> all 8760 hours.  We also set the system to "no economizer".
>
> *Z Smith, AIA, LEED AP BD+C *| Director of Sustainability & Building 
> Performance |***Eskew+Dumez+Ripple*| 365 Canal Street, Suite 3150 | 
> New Orleans, LA  70130 | 504.561.8686 |**eskewdumezripple.com 
> <http://www.eskewdumezripple.com/>
>
> *From:*Hall, Brendan [mailto:BHall at karpinskieng.com]
> *Sent:* Wednesday, March 13, 2013 3:40 PM
> *To:* Z Smith; equest-users at lists.onebuilding.org
> *Cc:* Corey Squire
> *Subject:* RE: [Equest-users] Does eQuest properly account for latent 
> loads in infiltration & ventilation?
>
> One note about using heating and cooling degree days for that purpose 
> is that ventilation air is usually locked out during unoccupied times 
> so the annual total would be much lower. From a quick read of the 
> paper you cited it seems that they used all 8760 hours. You would need 
> to isolate the occupied hours when the economizer is not likely to be 
> in use to get a more accurate number.
>
> Brendan Hall
>
> *From:*equest-users-bounces at lists.onebuilding.org 
> <mailto:equest-users-bounces at lists.onebuilding.org> 
> [mailto:equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Z Smith
> *Sent:* Wednesday, March 13, 2013 3:26 PM
> *To:* equest-users at lists.onebuilding.org 
> <mailto:equest-users at lists.onebuilding.org>
> *Cc:* Corey Squire
> *Subject:* [Equest-users] Does eQuest properly account for latent 
> loads in infiltration & ventilation?
>
> We are interested in using eQuest to evaluate the impact of improved 
> air-sealing or changed outdoor air ventilation rates.  Even with very 
> simple test case buildings and run-of-the-mill HVAC systems, we get 
> results that make it seem as if eQuest is not accounting for the 
> latent component of outdoor air brought into a building.
>
> We are using Lew Harriman et al.'s 1997 ASHRAE Journal paper on the 
> "Ventilation Load Index" as a reality check.
>
> http://masongrant.com/pdf_2008/Ventilation_Loads.pdf
>
> The authors characterize the total load (latent and sensible) for 
> bringing 1 cfm continuously into the building for a number of cities.  
> It's interesting to consider two cities with comparable CDD but very 
> different latent loads for ventilation air:
>
> New Orleans  CDD=2776    VLI=12.3 [latent] + 1.8 [sensible] =14.1 
> ton-hrs/yr
>
> Tucson       CDD=3017    VLI= 1.5 [latent] + 3.0 [sensible] = 4.5 
> ton-hrs/yr
>
> The VLI is the cumulative load to bring 1cfm from whatever the hourly 
> condition is in the TMY2 file to 75°F, 50% RH (65gr/lb).  Its units 
> are ton-hr/yr for convenience, converted to annual kBtu by multiplying 
> VLI by12 kBtu/ton-h.
>
> So, for example, if we have a building with 2,000ft2 of floor area and 
> a volume of 20,000ft3 with a ventilation rate of 1ACH, outdoor air is 
> being introduced to the building at 20,000/60 = 333cfm.  The annual 
> cooling & dehumidification load associated with this airflow is 333 x 
> 14.1 = 4,695 ton-hrs/yr in New Orleans and 1,383 ton-hrs/yr in 
> Tucson.  If, for simplicity, we assume the air system brings this air 
> to 75°F, 50% RH with a SEER of 13 kBtu/kWh in both cities, then the 
> energy consumption associated with 1ACH  for this 2000ft2 building is 
> 4,334 kWh in New Orleans and 1,383 kWh in Tucson. The impact on 
> building site EUI will be 7.4 kBtu/sf/yr in New Orleans and 2.4 
> kBtu/sf/yr in Tucson -- a difference of about 5kBtu/sf/yr.  If one 
> were to consider ventilating at 10ACH, then the impact would be 10x as 
> large---74kBtu/sf/yr in New Orleans vs 24 kBtu/sf/yr in Tucson---a 
> difference of ~50 kBtu/sf/yr.
>
> When we run an eQuest model of a hypothetical 2000ft2 building with no 
> windows (to rule out solar gain differences) and no heating system, 
> only cooling, we find that the EUI does increase with ACH at the two 
> locations---but there is almost no difference in how the predicted EUI 
> rises with ACH for the two cities with wildly different VLI.  The EUI 
> rises by the same ~35 kBtu/sf/yr when going from 1ACH to 10ACH at both 
> locations.
>
> Results summarized below for total building EUI (kBtu/sf/yr):
>
>                     eQuest             Simple model using VLI
>
>   ACH     New Orleans     Tucson      New Orleans      Tucson
>
>     1          42           40 36             30
>
>    10         76           74 126             74
>
> ------    ----------------------- -----------------------
>
>   1->10        34           34 90             44
>
> (This windowless test building had R10 walls, R20 roof, R5 floor -- 
> but all we are interested in is the **difference** in total EUI 
> associated with the increased ACH, which shouldn't depend on these 
> choices).
>
> Z Smith, AIA, LEED AP BD+C | Director of Sustainability & Building 
> Performance | Eskew+Dumez+Ripple | 365 Canal Street, Suite 3150 | New 
> Orleans, LA  70130 | 504.561.8686 | eskewdumezripple.com
>
>
>
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