[Equest-users] Air cooled chillers versus water cooled chillers

Thu Oct 29 00:42:57 PDT 2015

Hi Rathanashree,

22W/gpm is the requirement of baseline model not for proposed case and it
has to be modeled for both primary & secondary pump in baseline.

Warm Regards
Sambhav

On Wed, Oct 28, 2015 at 5:03 AM, Cam Fitzgerald <cam at energyopportunities.com
> wrote:

> Good morning, all!
>
>
>
> A little insight on this issue. There is an ASHRAE Interpretation
> ASHRAE/IES IC 90.1-2007-14 that indicates the chilled water pump power
> allowance is to be split between the primary and secondary pumps in the
> Baseline model. I am unsure of the date the interpretation was issued, but
> if using Appendix G modeling protocol for any other purpose other than LEED
> projects, this guidance should be followed from the issue date on. This
> ASHRAE Interpretation was implemented for LEED projects by LEED
> Interpretation 10299 which was issued on 01/01/2014 and all projects
> registered after that date must follow this protocol as described in the
> interpretation.
>
>
>
> Hope this helps.
>
>
>
>
>
> Cam Fitzgerald
>
>
>
> Energy Opportunities/a 7group company
>
>
>
>
>
>
>
> *From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] *On
> Behalf Of *Rathna Shree
> *Sent:* Wednesday, October 28, 2015 1:39 AM
> *To:* David Eldridge; Bosch, Crina; Bishop, Bill; Sambhav Tiwari
>
> *Cc:* Equest Users Mailing List
> *Subject:* Re: [Equest-users] Air cooled chillers versus water cooled
> chillers
>
>
>
> Sorry, i meant primary and secondary pumps.
>
>
>
> Now the main issue is my proposed case with variable primary and air
> cooled chillers are performing equal or better than the baseline case. Is
> this possible?
>
>
>
>
>
> On Wednesday, 28 October 2015 2:42 AM, David Eldridge <
> DEldridge at grummanbutkus.com> wrote:
>
>
>
> I didn’t follow this thread all of the way earlier, but the idea might be
> that in the baseline case the 22 W/gpm is split between the primary and
> secondary pumps in some manner.
>
>
>
> The proposed case has the design values to go from, and may be primary
> only or primary secondary – whatever the proposed motor power and
> configurations is, use that.
>
>
>
> David
>
>
>
>
>
>
>
>
> David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
>
> *Grumman/Butkus Associates*
>
>
>
>
>
>
>
>
> *From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org
> <equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *Bosch, Crina
> *Sent:* Tuesday, October 27, 2015 3:32 PM
> *To:* Rathna Shree <rathnashreep at yahoo.in>; Bishop, Bill <
> bbishop at pathfinder-ea.com>; Sambhav Tiwari <tiwari.sambhav at gmail.com>
> *Cc:* Equest Users Mailing List <equest-users at lists.onebuilding.org>
> *Subject:* Re: [Equest-users] Air cooled chillers versus water cooled
> chillers
>
>
>
> Rathnashree,
>
>
>
> I didn’t understand your statement that “22W/gpm has to be split between
> base and proposed case based on a ASHRAE interpretation.”
>
> As Bill mentioned below, for the Baseline Model The CHW pump power must be
> calculated as 22 W/gpm. Usually , you check in PV-A report your autosized
> gpm and that way you can calculate you pump power and see if it’s input
> correct.
>
> The Proposed Model Pump power must be input as scheduled per design which
> is totally different than ASHRAE requirement.
>
>
>
> Hope this may help,
>
> Crina.
>
>
>
>
>
> cbosch at karpinskieng.com
>
>
>
>
>
> *From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org
> <equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *Rathna Shree
> *Sent:* Tuesday, October 27, 2015 3:49 AM
> *To:* Bishop, Bill; Sambhav Tiwari
> *Cc:* Equest Users Mailing List
> *Subject:* Re: [Equest-users] Air cooled chillers versus water cooled
> chillers
>
>
>
> Dear Sambhav/ William Bishop
>
>
>
> Thank you for the replies.
>
>
>
> I have modelled the baseline case as per the requirements of Appendix G
> (Pumps, cooling tower power etc is modeled as per ASHRAE 90.1 2007). Just
> to confirm, 22W/gpm has to be split between base and proposed case based on
> a ASHRAE interpretation.
>
>
>
> With the exact modeling, i am getting result where variable primary
> pumping system - air cooled screw chillers are performing almost equal or
> better than baseline centrifugal chiller. These results seem little
> surprising. So i am unsure whether it is correct.
>
>
>
> It would be really helpful if the experts can confirm the results.
>
>
>
> Thank you.
>
>
>
> Regards,
>
> Rathnashree
>
>
>
>
>
>
>
>
>
> On Monday, 19 October 2015 7:27 PM, "Bishop, Bill" <
> bbishop at pathfinder-ea.com> wrote:
>
>
>
> Rathna,
>
> There are several inputs in eQUEST that impact your CHW plant pumping
> energy as modeled for Appendix G:
>
> 1.)    CHW pump power should be 22 W/gpm per G3.1.3.10. I don’t recall
> how “official” it is but many on this forum interpret this as for the
> entire primary/secondary pumping, meaning it should be split between the
> primary and secondary pumps. (For example, 10 W/gpm for the primary loop
> pump and 12 W/gpm for the secondary loop pump.) Splitting vs. not splitting
> is one of the major influences of Baseline pump power.
>
> 2.)    CW pump power should be 19 W/gpm per G3.1.3.11.
>
> 3.)    CHW coils should use CHW-VALVE-TYPE of TWO-WAY to facilitate
> variable flow through the secondary loop, regardless of using a
> variable-speed drive for the secondary loop pump (for cooling capacity ≥
> 300 tons) or “riding the pump curve” with a single-speed pump (cooling
> capacity < 300 tons).
>
> 4.)    The loop HEAD-SETPT-CTRL and HEAD-SENSOR-LOCN have major
> influences on pump energy. There is no requirement in Appendix G. that
> specifies the type of control. In order of least to best efficiency, the
> settings are:
>
> a.      FIXED; AT-PUMP
>
> b.      FIXED; ENTERING-LOOP
>
> c.      FIXED; AT-COILS
>
> d.      VALVE-RESET; n/a
>
> I think FIXED, AT-COILS is a reasonable setting for both the Baseline and
> Proposed models, unless the Proposed design has the controls to survey the
> positions of all coils and implement the VALVE-RESET strategy, and then I
> use that in the Proposed.
>
> 5.)    LOOP-OPERATION impacts all CHW end-uses (cooling, pumping, heat
> rejection) especially if cooling is not needed year-round. This is also not
> specified in Appendix G. STANDBY keeps the CHW plant running when any
> systems with CHW capability are running. DEMAND-ONLY turns the CHW plant
> off unless there is a coil or process load for that hour. I think either
> setting is fair as long as it is kept identical between the Baseline and
> Proposed models.
>
> Besides pumping energy, there is an easily-overlooked Baseline requirement
> per G3.1.3.11 of axial fan cooling towers with two-speed fans. Table 6.8.1G
> shows the minimum performance requirement of ≥38.2 gpm/hp. You have to
> calculate the fan kW from this based on the autosized tower flow and enter
> it as FAN-KW/FLOW or EIR. The eQUEST default EIR of 0.0105 for open towers
> is actually more efficient than the Table 6.8.1G requirement.
>
>
>
> Regards,
>
> ~Bill
>
>
>
> *William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers &
> Architects LLP*
>
> *Senior Energy Engineer*
>
> [image: cid:image001.jpg at 01D110D0.903D6640]  [image:
> cid:image002.jpg at 01D110D0.903D6640]
>
>
>
> 134 South Fitzhugh Street                 Rochester, NY 14608
>
> *T: (585) 698-1956*                        F: (585) 325-6005
>
> bbishop at pathfinder-ea.com <wbishop at pathfinder-ea.com>
> www.pathfinder-ea.com
>
> [image: http://png-5.findicons.com/files/icons/977/rrze/720/globe.png]Carbon
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>
> *From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org
> <equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *Rathna Shree
> *Sent:* Monday, October 19, 2015 1:03 AM
> *To:* Sambhav Tiwari <tiwari.sambhav at gmail.com>
> *Cc:* Equest Users Mailing List <equest-users at lists.onebuilding.org>
> *Subject:* Re: [Equest-users] Air cooled chillers versus water cooled
> chillers
>
>
>
> Hi Sambhav,
>
>
>
> Does that mean, air cooled chillers with variable primary pumping system
> performance is almost equivalent or better than the ASHRAE 90.1 2007
> defined water cooled centrifugal chiller system?
>
>
>
> Regards,
>
> Rathnashree
>
>
>
>
>
> On Saturday, 17 October 2015 12:57 PM, Sambhav Tiwari <
> tiwari.sambhav at gmail.com> wrote:
>
>
>
> Hi Rathanashree,
>
>
>
> For me the results seems to be alright
>
>
>
> 1 Being a air cooled chiller with less COP than baseline water cooled your
> compressor energy consumption is increasing which is clear from the results
> .
>
>
>
> 2 Now there is a debate going these day to replace ( constant primary &
> variable secondary pumps) with variable primary pump system although many
> HVAC experts  advocate against it that it can have negative impacts on
> chiller too.But definitely it will save energy consumption under pumps
> which is clear from your results your proposed case is left only with VFD
> based primary pump compared with baseline of ( constant primary+variable
> secondary+constant condenser water pumps) therefore pumps energy is too
> less and justified to me.
>
>
>
> 3 Your cooling tower energy consumption will be nil in proposed case being
> a air cooled system that is also fine.
>
>
>
> But the main driver or  you can say main ECM in your analysis is variable
> primary and no secondary chiller which is contributing siginifant savings
> in pumps along with no cooling tower present hence your over all energy
> saving are positive.
>
>
>
> Hope this may help.
>
>
>
> Warm Regards
>
> Sambhav
>
>
>
> On Fri, Oct 16, 2015 at 11:50 PM, Rathna Shree <rathnashreep at yahoo.in>
> wrote:
>
> Dear All,
>
>
>
> A project has 14 floors and 3.5 lakhs sq.ft. of conditioned area. The
> project is going for LEED certification. The baseline HVAC system will be
> Variable air volume system with water cooled centrifugal chiller of COP
> 6.1. LPD is maintained at 0.7W/sft. Building envelope is more or less equal
> to baseline case. In this scenario, the proposed HVAC system is air cooled
> screw chillers with variable primary pumping system. Even though the
> project is getting negative results in cooling category, there is a huge
> savings from pumps which is compensating for the negative in cooling energy
> consumption. Ultimately, the overall plant energy consumption (Cooling,
> heat rejection, pumps) is lesser in proposed case than base case. I am
> surprised with the result as i believe for such a building, water cooled
> chillers work more efficiently. For more clarity, the results are given as
> below:
>
>
>
> Base case: Cooling: 14,26,659 KWH, Heat rejection: 1,23,357 KWH, Pumps:
> 426,506 KWH
>
> Proposed case: Cooling: 17,89,814 KWH, Heat rejection: 0 KWH, Pumps:
> 62,264 KWH
>
>
>
> These are results are for default chiller curves in both the cases. If air
> cooled part load values are used, then cooling energy consumption further
> reduces in proposed case. Then can it be concluded that air cooled with
> primary variable pumping system is a good alternative to use.
>
>
>
> Is this conclusion appropriate? Are the results correct? Please help.
>
>
>
> Regards,
>
> Rathnashree
>
>
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