Francesco,
For a VAV system, you may use a single air loop for both (all) zones on the floor.
In the Sizing:System object, you will specify “Central cooling design supply air temperature” at ~12C. normally “Central heating design supply air temperature” is the about the same.
For the Sizing:Zone object:
“Zone cooling design supply air temperature” is also ~12C
“Zone heating design supply air temperature” is (Tsetpoint + 11C). Each zone, of course, may have a different value for (Tsetpoint + 11C).
Note that, it is normal for reheat coils to operate in the summer, so the boiler or other heating source should remain available. Also note that unless you specify setpoints carefully, E+ will use the heating setpoint for cooling in a reheat system. (It is trying to be energy conserving J)
p.s., Engineers in the US have an advantage when reading the English-based ASHRAE 90.1 – we are familiar with the abbreviations like “w.c.”! I’m glad that you discovered the meaning.
James V Dirkes II, PE, BEMP, LEED AP
The Building Performance Team Inc
1631 Acacia Drive, Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of FrancescoP
Sent: Friday, August 17, 2012 7:39 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Sizing according to ASHRAE 90.1
Thank you very much for your explanation, James!
I give an example: I have on one floor two zones having two different summer set-points Tsum1 and Tsum2 and I have to model System 5 (Packaged VAV with Reheat). During the summer the supply air temperature shall be Tsum1-11°C for the first zone and Tsum2-11°C for the second zone, therefore the only solution that I have is to model two separate Air Loops for the two zones, isn't it?
For the winter season the system is more flexible because there is a reheat coil in every zone.
About pressure drop adjustments in the "User's Manual for ANSI/ASHRAE/IESNA Standard 90.1-2007" I found an interesting explanation: "The basic brake horsepower allowance is based on the assumption that return air passes through an open plenum on its way back to the fan system. For systems where all the return air is ducted back to the return, an additional pressure drop allowance of 0.5 in. w.c. is allowed".
I discovered that "in wc" = "inches of water column"….
Best Regards
Francesco
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Jim Dirkes <jim@...> wrote:
>
> Francesco,
> Comments interspersed below
>
>
> James V Dirkes II, PE, BEMP, LEED AP
> The Building Performance Team Inc
> 1631 Acacia Drive, Grand Rapids, MI 49504
> 616 450 8653
>
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of FrancescoP
> Sent: Thursday, August 16, 2012 8:49 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: [EnergyPlus_Support] Sizing according to ASHRAE 90.1
>
>
>
> I have some doubts concerning the sizing of baseline equipment according to APPENDIX G of ASHRAE 90.1.
>
> 1) Paragraph G3.1.2.8 of ASHRAE 90.1 states: "System design supply airflow rates for the baseline buildings design shall be based on a supply-air-to-room-air temperature difference of 11°C". I interpret that statement in the following way: if the internal set-point temperature during the winter season is Twin then system design supply airflow rates have to be calculated considering a design supply airflow temperature of Twin + 11°C and if the internal set-point temperature during the summer season is Tsum then system design supply airflow rates have to be calculated considering a design supply airflow temperature of Tsum - 11°C. Is my interpretation correct?
>
> This is correct.
> Does the procedure of paragraph G3.1.2.8 of ASHRAE 90.1 regard only the sizing run or even the simulation with the test reference year?
> The HVAC system of the baseline is "Packaged VAV with reheat".
>
> E+ performs sizing coincident with simulation. If you elect to make a separate "sizing" run, the same criteria, including "Autosize", must be used for both.
>
> In EnergyPlus can I satisfy the request of paragraph G3.1.2.8 using Controller:WaterCoil?
>
> This object does not affect sizing at all. The criteria that E+ uses are contained in the Sizing:System and Sizing:Zone objects.
>
> 2) In order to calculate the baseline fan motor power I have to calculate the parameter A according to tables 6.5.3.1.1A and 6.5.3.1.1B. Shall I model "fully ducted return and/or exhaust air systems" for every return or relief fan? In the IP edition it is specified that the adjustment is valid only for WCs, but that specification is not present in the SI edition. I don't understand why.
>
> The Baseline model must use the power adjustments consistent with the Proposed model. E.g., if the Proposed model is fully ducted, the Baseline fan power should include that adjustment.
>
> p.s., I am guessing that "WC" is a "water closet", but I am not sure ....
>
> Shall I consider a pressure drop adjustment equal to
> 125 Pa (0.5 in IP units)
> for every "fully ducted return and/or exhaust air system" (see table 6.5.3.1.1B)?
> If on one floor there are three WCs where there is a mechanical extraction system. In the baseline model I modelled those WCs as connected to a AHU having both supply and exhaust fans. Shall I consider a total pressure drop adjustment equal to 375 Pa (= 3 x 125 Pa)?
>
>
> The rooms which have mechanical extract systems should be modeled as having a Fan:ZoneExhaust. The pressure adjustments do not normally apply to these. (A pressure adjustment would apply to something like a laboratory extract system which has mechanized dampers for flow control.)
>
> With Regards
> Francesco Passerini
>
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