[Equest-users] Written explanation of the System Sizing Logic asshown on the SYSTEM Tab

[deepika khowal]

I had similar experience about oversized system in summary reports.
I now look at the total cooling loads from SS-D report in kbtu/hr and divide
it by 12 (1ton=12000 btu). I also add a factor of 15% as that cooling load
may be undersized.

This number is approximate correct to what a typical system should be based
on trace calcs.

Deepika

On Mon, Sep 26, 2011 at 4:29 PM, Nick Caton <ncaton at smithboucher.com> wrote:

> Hey John,****
>
>
> Sounds like a shotgun of queries… here’s a shotgun response =):****
>
> ** **
>
> Everything you see in the airside summary tab is the result of some
> combination of inputs – nothing pops out of thin air so you should be able
> to trace any one result to determine what combination of inputs/schedules is
> producing different results.  Note the “totals” for each zone are summed on
> the line describing the system.****
>
> ** **
>
> Defaults are neither good nor bad.  Sometimes they’re quite off.  Sometimes
> they do a better job than any assumption you’d make otherwise.  A big part
> of QC is reviewing to ensure the defaults are appropriate where leveraged.
> ****
>
> ** **
>
> With a too-high cooling capacity, I’d start looking at whether your loads
> are off and/or your airflows are being sized incorrectly… but first you want
> to ensure your unmet hours aren’t way out of whack – that’s a sign something
> isn’t functioning or reacting to your building quite right and needs to be
> addressed.  Remember unmet hours are symptoms of another problems, and not
> always capacity (heating/cooling/airflow).  You’ll run yourself in circles
> if you try to treat them as the primary problem.  Which spaces have them,
> the time of day, and the time of year they occur are all potentially clues
> as to what’s really going on.  ****
>
> ** **
>
> Once your unmet hours are either zero or reigned in to a low comfy figure,
> you’re ready to get your loads in order.  Get the load calc output reports
> (and ideally the person who ran them, if not yourself) handy and open up
> your model.****
>
> ** **
>
> Loads are in 2 categories: “ventilation” and “everything else.”  You can
> quickly assess whether the ventilation air loads are appropriate for your
> spaces using the airside summary tab – where the number seems significantly
> off for a system line, check the ventilation quantities and # of people in
> associated zones.  Focus on spot checking higher-occupancy spaces (i.e.
> gyms, cafeteria, conference rooms, etc.) to ensure those are in sync with
> expectations/sizing.  If the quantity of people seems right but the
> ventilation air results are still off – move to checking your occupancy
> schedules and OA/person figures.  Note how eQuest makes design day schedules
> which will by default reference your ‘normal’ schedules - .  If you have an
> equipment schedule to follow, you can input the zone ventilation air
> directly, but making 50 people breathe like 10 will still result in 40
> people worth of heat load you’ll need to account for so I’d first try to get
> space populations into the right ballpark to get your auto-sized ventilation
> quantities in line.****
>
> ** **
>
> Once ventilation quantities are being sized in the correct ballpark, and if
> your auto-sized capacities are still off – you can review the other loads
> incident on a given space with the LS-B report.  Again spot check
> higher-load spaces for design heating/cooling conditions that seem out of
> whack with your loads run.  Pay close attention to little things applied
> everywhere, like plug load W/SF – small changes there can make a big
> difference.  Something way off here may also lead you to
> review/revise/correct your envelope/window properties or other internals.*
> ***
>
> ** **
>
> Airflow capacities are auto-sized based on only about a million variables
> (including everything affecting loads), so it’s hard to generalize where to
> start for every model.  They do however have a direct effect on coil
> capacities – so they definitely warrant attention to get into the right
> ballpark.  I’ve found however that when the loads are synced up correctly,
> airflows tend to follow – but pay attention to the effects of elevation
> (grr) and your system sizing factors which have a direct impact on CFM’s
> produced by eQuest. ****
>
>
> If you’re trying to assess system performance before and after
> significantly revising the space equipment loads, it follows your inputs
> should be stipulating carefully (not defaulting) the associated space
> equipment loads and the internal heat loads they contribute to the system.
> Servers by design generally do not put out what they are rated to take in
> without some diversity – give definition of those internals some careful
> thought from a heat-gain perspective.  This applies generally to all your
> internals – review the schedules to ensure you’re getting an appropriate
> degree of diversity!****
>
> ** **
>
> Noting your building is 50% glass – that in and of itself warrants extra
> attention towards whether your solar loads are in sync.  If not, it follows
> to review the items that affect solar loads:  glazing properties, shading
> (consider including stuff outside the building like neighboring buildings &
> trees), etc.****
>
> ** **
>
> Infiltration is something that can potentially have a great effect on any
> model’s heating/cooling capacities.  Don’t miss that when trying to QC/match
> others’ loads.****
>
> ** **
>
> …****
>
> ** **
>
> Well there’s a list =).  ****
>
> ** **
>
> ~Nick****
>
> ** **
>
> ** **
>
> [image: cid:489575314 at 22072009-0ABB]**
>
> * *
>
> *NICK CATON, P.E.***
>
> SENIOR ENGINEER****
>
> ** **
>
> Smith & Boucher Engineers****
>
> 25501 west valley parkway, suite 200****
>
> olathe, ks 66061****
>
> direct 913.344.0036****
>
> fax 913.345.0617****
>
> www.smithboucher.com* *****
>
> ** **
>
> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *John Aulbach
> *Sent:* Sunday, September 25, 2011 11:02 AM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] Written explanation of the System Sizing Logic
> asshown on the SYSTEM Tab****
>
> ** **
>
> My boss is a skeptic of the data presented in the System Sizing Tab that
> can be generated when you are the System screen and hit the Summary tab, and
> I don't have a good explanation.  We looked at a single office floor in the
> Southern California are, a floor with about 50% glass and about 29,000 sf.
> The System tab generated a size of 107 tons (installed tonnage for the floor
> was 80 tons). Most load information was defaulted.****
>
> ** **
>
> The installed tonnage was 80 tons and the unmet hours were few.****
>
> ** **
>
> When we increased the airflow slightly, the load size was 80 tons.  When we
> increased the total supply airflow double, the tonnage went to about 140
> tons.****
>
> ** **
>
> And, of course, the unmet hours varied, inconsistent of course between SS-R
> and SS-F and the System Sizing tab.****
>
> ** **
>
> All I am looking for is a detailed explanation of how the system sizing tab
> is generated. Obviously, this is not TRACE sizing routine, but there are
> some of us who must use this table to have a sense if a builidng has enough
> cooling after equipment (read-SERVERS) has been added to a floor.****
>
> ** **
>
> Can anyone who had had time to research this care to share their finds?***
> *
>
> ** **
>
> Thanks.****
>
> ** **
>
> John Aulbach.****
>
> ** **
>
> What is ****
>
> ** **
> ------------------------------
>
> *From:* Jun Furuta <JFuruta at energy-solution.com>
> *To:* "equest-users at lists.onebuilding.org" <
> equest-users at lists.onebuilding.org>
> *Sent:* Tuesday, September 20, 2011 1:39 PM
> *Subject:* [Equest-users] Modeling 2 stage cooling in a single zone
> packaged unit****
>
> Hello,****
>
>  ****
>
> I would like to model a packaged single zone AC with gas furnace that has
> two stage cooling with using two compressors. The system has an integrated
>  economizer and a constant speed fan.****
>
>  ****
>
> Is there a way to indicate two compressors in the PSZ system type or am I
> supposed to use the PVVT system, despite being a single zone system and not
> having neither a variable speed compressor or fan? And if the PVVT system
> type is to be used, any advice on configuring the system would be greatly
> appreciated.****
>
>  ****
>
> Thanks,****
>
>  ****
>
> -Jun****
>
>  ****
>
>  ****
>
>
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> ****
>
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