[Equest-users] Curve Coefficients

Arpan Bakshi arpanbakshi at gmail.com
Wed Feb 2 14:16:08 PST 2011
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John

You may have already looked over what the 2.1 manual has to offer as far as
explanation on this.

IV.71

H.  Calculate  the  cooling  part  load  ratio.

Some  central  systems  control  the  operation  of  the  central  cooling
 coil based  upon  temperature  signals  from  the  zone  thermostats
 (COOL-CONTROL  = WARMEST).  Other  central  systems  control  the
 operation  of  the  central cool ing  coil  based  upon  the  coil  exit
 air  temperature  (COOL-CONTROL  =  CONSTANT,  RESET,  or  SCHEDULED).  In
 the  latter  case,  the  controller  for the  cool ing  coil  has  a
 throttl ing  range.  As  the  temperature  of  the  air leaving  the  coil
 rises  and  falls  within  the  controller's  throttling  range, the
 controller  varies  the  operation  of  the  coil,  increasing  or
 decreasing the  output  of  the- coil.  The  action  of  the  controller
 must  be  simulated because  it  will  have  an  effect  on  the  coil
 surface  conditions  and  thus also  on moisture  removal  by  the  coil.
 Because  this  controller  responds to  the  temperature  of  the  air
 stream,  the  sensible  part  load  ratio  of  the coil  or  unit will  be
 calculated.  This  value  will  then  be  used  the  following  hour  to
 modify  the  coil  exit  air temperature  as  a  function  of  controller
 set  point,  coil  capacity,  and  controller  throttling  range
 (see DKTEMP  algorithm  description).

First,  the  program  calculates  the  total  and  sensible  cool ing
 equipment capacities  (QCT  and  QCS)

where

QCT  =  COOLING-CAPACITY  *  QCMl  (IV.178)

and

QCMl  =  CVAL(COOL-CAP-FT,EWB,EDB)  [COOL-CAP-FT  is  a  correction
function  to  the  total  cooling  capacity  to  adjust  for  off-rated
entering wet-bulb  and  entering  dry-bulb  temperatures]

and

QCS  = COOL-SH-CAP  * QCM2  {however,  for  direct  expansion  units,  QCS
 =
(COOL-SH-CAP  * QCM2)  +  [CONS{l)  * CFM  *  (1.0  - CBF)  *
(TM  - 80.0)]}

or

QCS  =  QCT,  whichever  is  smaller,

where

QCM2  = CVAL{COOL-SH-FT,EWB,EDB)  [COOL-SH-FT  is  a  correction  function,
similar  to  QCMl,  but  to  the  sensible  portion  of  the  total
cooling  capacity].

The  equipment  cooling  part  load  ratio  (PLRC)  and  the  sensible  part
 load
ratio  «PASTPLRC»  are  then  calculated,


PLRC  =  QC/QCT

and

<PASTPLRC>  = QC - QCLAT / QCS

For  direct  expansion  equipment,  the  electric  power  consumed  by  the
 heating
element  in  the  crankcase  is  calculated  as  CRANKCASE-HEAT  *  (1.0  -
PLRC).




2011/2/2 Nick Caton <ncaton at smithboucher.com>

>  Hi John,
>
>
>
> To answer your first question… For a DX cooling system, my understanding is
> that COOL-EIR-FT’s temperatures are the outside drybulb (at the
> condenser/heatpump) and the entering wetbulb temperature at the evaporator
> (mixed air conditions).  This mirrors how packaged equipment
> efficiencies/capacities are presented in manufacturers’ literature.  See
> attached discussion for an example.
>
>
>
> I understand COOL-CAP-FT and COOL-SH-FT curves work from the same
> temperatures.
>
>
>
> To your second question… I’m with you!
>
>
>
> I’d like to see the equation for “hourly electricity consumption” for an
> air-cooled DX process written out in its entirety showing all the affecting
> – I was searching for something analogous to [Volume 2: Dictionary > HVAC
> Components > CHILLER > Chiller Energy Consumption] for airside DX cooling
> systems a while ago and also came up empty-handed.  I have a hunch the
> effects of the 3 bypass curves (which are a mystery to me) may have
> something to do with the hourly calculated total capacity and/or EIR though…
> perhaps those need to work their way into your equation?
>
>
>
> Regarding the hourly results you’re using to check your work… I’m not sure
> whether those are the correct figures to work from, but I’d caution to be
> mindful of the wonky effects of altitude on calculated capacities/airflows
> when working with hourly outputs – recent discussion on the list brought
> more to light on this topic – and the effects are more pervasive than I
> originally thought…
>
>
>
> ~Nick
>
> [image: cid:489575314 at 22072009-0ABB]**
>
> * *
>
> *NICK CATON, E.I.T.***
>
> PROJECT ENGINEER
>
> Smith & Boucher Engineers
>
> 25501 west valley parkway
>
> 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 *Grando, John
> *Sent:* Wednesday, February 02, 2011 12:18 PM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] Curve Coefficients
>
>
>
> I'm basically trying to figure out how eQUEST comes up with the total
> Electric consumption for a DX coil.  I thought it was the below
>
>
>
> Total Capacity * Capacity Curve [T] * Total EIR * EIR Curve [T] * EIR Curve
> [PLR] but it's not coming out exactly the same.  Does anyone have any input
> for what I'm missing.  The attached .xls is an example for one day.  The
> total capacity is 79.983 kBTU/Hr and the EIR is  0.2722.
>
>
>
>
>
>
>
> *John Grando** **LEED AP**| **Mechanical Engineer
> *Phone: 212-615-3705 | Fax: 212-615-3700
> jgrando at cosentini.com
>
> *Cosentini Associates - A Tetra Tech Company
> *Two Pennsylvania Plaza - Third Floor - New York, NY 10121
> www.cosentini.com
>
>
>
>
>
>
>
>
> NOTICE OF CONFIDENTIALITY This E-mail message and its attachments (if any)
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>
>
>
>
>
> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Grando, John
> *Sent:* Wednesday, February 02, 2011 7:55 AM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] Curve Coefficients
>
>
>
> Hello,
>
>
>
> For the curve COOL-EIR-FT the two inputs for a water loop heat pump system
> are "entering wetbulb temperature" and "entering water temperature".  I
> understand that the water temperature is the condenser water, but is the
> entering wetbulb temperature for the evaporator side?
>
>
>
>
>
> *John Grando** **LEED AP**| **Mechanical Engineer*
>
>
>
>
>
>
>
>
> NOTICE OF CONFIDENTIALITY This E-mail message and its attachments (if any)
> are intended solely for the use of the addressees hereof. In addition, this
> message and the attachments (if any) may contain information that is
> confidential, privileged and exempt from disclosure under applicable law. If
> you are not the intended recipient of this message, you are prohibited from
> reading, disclosing, reproducing, distributing, disseminating or otherwise
> using this transmission. Delivery of this message to any person other than
> the intended recipient is not intended to waive any right or privilege. If
> you have received this message in error, please promptly notify the sender
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>
>
>
>
> ---------- Forwarded message ----------
> From: "Nick Caton" <ncaton at smithboucher.com>
> To: "John T. Forester" <JohnTF at BVHis.com>, <
> equest-users at lists.onebuilding.org>
> Date: Wed, 19 Jan 2011 17:43:56 -0600
> Subject: RE: [Equest-users] Air-Cooled EIR Curves
>
> Hi John,
>
>
>
> Hmm… intuitively I think this makes sense, but I haven’t actually gone
> through creating a set of custom packaged DX curves before – lets’ first
> verify we’re looking at the same definition:
>
> Volume 2: Dictionary > HVAC Components > SYSTEM > Cooling Equipment > DX
> Cooling
>
> *COOL-EIR-FT*
>
> Takes the U-name of a bi-linear or bi-quadratic curve that describes the
> Electric Input Ratio for cooling *as a function of entering wet-bulb
> temperature and outdoor dry-bulb temperature (for direct expansion coils)*or entering wet-bulb temperature and entering water temperature for a Water
> Loop Heat Pump (HP) system. At ARI conditions, the value of the curve should
> be 1.
>
> I’m pretty sure the entering wet-bulb is that found entering the evaporator
> coil – the mixed air about to be conditioned.  If you check out a typical
> set of packaged DX unit performance tables (If you want a specific example
> to follow along, I’ve just cracked open an engineering guide for the
> Lennox LGH series<http://tech.lennoxintl.com/C03e7o14l/HS7CbNGGFw/ehb_lgh_abox_1010.pdf>*
> to page 21), you’ll find they’ve got OA DB along one axis (85/95/105/115)
> and Entering WB along the other axis (63/67/71).   It would appear the same
> tables could also be used to reference data for COOL-CAP-FT and COOL-SH-CAP
> curves.
>
>
>
> Make sense now?
>
>
>
> ‾Nick
>
>
>
> *Disclaimer: I have no particular ties or intent/business to advocate
> Lennox over their competitors – all of their major competitors publish
> similar reference/sizing tables, and this particular unit’s guide just
> happened to be near the top of my reference stack.
>
>
>
> [image: cid:489575314 at 22072009-0ABB]**
>
> * *
>
> *NICK CATON, E.I.T.***
>
> PROJECT ENGINEER
>
> Smith & Boucher Engineers
>
> 25501 west valley parkway
>
> 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 T.
> Forester
> *Sent:* Wednesday, January 19, 2011 4:50 PM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] Air-Cooled EIR Curves
>
>
>
> Quick question,
>
>
>
> When creating custom EIR fT and EIR fPLR curves for air-cooled packaged DX
> units with digital scroll compressors, what are the two independent
> variables?  The DOE2 help says to use entering wet-bulb and outside air
> dry-bulb.  Where is the entering wet-bulb temperature measured?
> Intuitively, this doesn’t seem correct to me.
>
>
>
> Thanks,
>
>
>
> John
>
>
>
> John T. Forester, P.E., LEED AP, Mechanical Design Engineer *I BVH
> Integrated Services I** *617.658.9008 tel *I** *617.244.3753 fax *I** *One
> Gateway Center Suite 506, Newton MA 02458 *I www.bvhis.com I Hartford ●
> New Haven ● Boston*
>
>
>
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-- 



Arpan Bakshi
00 1 646 704-2880
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