[Bldg-sim] PTHP Baseline outperforming VAV

Cheney chenyu73 at gmail.com
Mon May 23 18:55:27 PDT 2011


Hi Marcus,

Also pay attention to better glass in the proposed design. In a
cooling-dominated building, better window means the heat can not easily
escape from the building. You will not easily get credit from improving your
window here.

Regards,

Cheney

LinkedIN @ http://ca.linkedin.com/pub/yu-cheney-chen/27/637/72b



On Mon, May 23, 2011 at 3:18 PM, James V Dirkes II, PE <
jim at buildingperformanceteam.com> wrote:

> Dear Marcus,
>
> ·         It seems that your Baseline system, at >5 floors, should be VAV
> with a chiller instead of a heat pump (using LEED 2009).
>
> ·         As modeled, your baseline DOES have a notably higher COP, so it
> may well use less energy.  *Part load performance* will have a significant
> effect, so you may want to check and compare  those curves.
>
> ·         Also check pump  delta T and total pressure drop.  If you
> continue with a non-chiller system, pump energy is  a significant factor.
> If your Baseline becomes a chiller system, pump energy will probably become
> similar.
>
> ·         Check fan total pressure drop for each system since your fan
> power is significantly larger in the Proposed system.
>
> ·         In the US, it is common to apply occupancy sensors on a LEED
> project and ASHRAE 90.1 allows a 10% power reduction when these are used.
> You are not taking advantage of that and may want to do so.
>
>
>
> *The Building Performance Team
> **James V. Dirkes II, P.E., BEMP , LEED AP
> *1631 Acacia Drive NW
> Grand Rapids, MI 49504
> 616 450 8653
>
>
>
> *From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Marcus
> *Sent:* Monday, May 23, 2011 4:24 PM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] PTHP Baseline outperforming VAV
>
>
>
> Hi all,
>
> Having some difficulty in an App. G model for a 6-floor 14,000 m2 GFA Hotel
> in zone 1B (Abu Dhabi). Assuming standard design for each, should a proposed
> VAV system out-perform window AC units (the baseline)?
>
> Proposed:
> VAV with 2 Air-cooled centrifugal chillers, chiller COP = 3.1 (2.8 if
> condenser fan energy included)
> Envelope - Better windows decrease heating demand by 8% rest of envelope is
> minimum required for compliance
>
> Baseline:
> System Packaged terminal heat pump, COP = 3.52
>
> Using Energyplus v6.0 the results are;
>
> Site Energy in End Uses                  BL   Proposed   COP5
>                                          MWh     MWh     MWh
>                        Space Cooling    747.5  1052.0   715.6
>                       Heat Rejection      0.0     0.0     0.0
>                        Space Heating      1.3     0.1     0.1
>                                Pumps      0.0    60.0    60.0
>                      Fans - Interior     42.2   137.7   137.7
>                      Fans - Car park      0.0     0.0     0.0
>                    Interior Lighting    530.5   530.5   530.5
>                    Exterior Lighting      0.0     0.0     0.0
>                Service Water Heating      0.0     0.0     0.0
>         Receptacle/Process Equipment    146.3   146.3   146.3
>                Data Centre Equipment      0.0     0.0     0.0
>             Elevators and Escalators      0.0     0.0     0.0
>                    Total Site Energy   1467.9  1926.6  1590.2
>
> I have the energy for the baseline, the proposed with COP = 3.1, and then
> trying COP = 5. It seems that even if we drastically increase the COP of the
> chiller plant in the proposed VAV system, we still can't get any energy
> savings. Is this realistic, an artifact of the simulation, or just an error
> on my part?
>
> Any guidance would be appreciated,
>
> Marcus
> --
> Marcus Jones, LEED AP, M.Sc.
> *Freelance energy consultant*
> *Vienna, Austria*
>
>
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