Re: [EnergyPlus_Support] HVAC sizing

An interesting discussion point. We oversize equipment to mitigate user complaints. Funny enough, even ASHRAE lets us oversize heating by a safety factor of 1.2 and cooling by 1.15. The manufacturers of equipment like chillers design their equipment with the 95 percentile for hours at a specific part-load relative to the full load design desired. Because people have been sizing fairly consistently for so long, the matching equipment have become more tailor-made for the real situation.

The correct way to size would be to do a good energy simulation and parametrically swap out different equipments with real operating efficiency curves and converge on a best combination (as you can do easily in designbuilder now FYI) . I've yet to see a building owner pay for that. And as the space allocation for the physical equipment is determined at the earliest design stage, a simulation of this sort is not really helpful as to much is still in flux. Having too little space for equipment is a horror so i'm all for oversizing at the early stages.

On 1 Aug 2018 4:09 am, "Joe Huang YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Although this has been the standard procedure for defining the heating design day, I question the underlying logic and think that will lead to oversizing. If the building is unoccupied, i.e., no occupants, no lights, no equipment, then why would it be heated to standard operating levels? I understand combining all the worst case conditions to get a design load, but not when those worst case conditions tend to exclude some others from ever occurring.

Joe
Joe Huang
White Box Technologies, Inc.
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On 7/31/2018 11:47 AM, Jim Dirkes jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support] wrote:
Whatever you specify as applicable on a Winter DesignDay is included.. Most designers calculate heating loads, however, with zero lights (or maybe 5% for security lights), zero equipment and zero people.

Most of the time, this makes sense, e.g., a long holiday such as Christmas or New Year, when everyone is gone and the building is quiet and dark. the Schedules might look something like:

SCHEDULE:COMPACT

Sched_PeopleAssembly

Fraction

Through: 12/31

For: Weekdays

Until: 8:00,0.00

Until: 11:00,0.20

Until: 18:00,0.80

Until: 22:00,0.20

Until: 23:00,0.10

Until: 24:00,0.00

For: Saturday

Until: 8:00,0.00

Until: 11:00,0.20

Until: 21:00,0.60

Until: 22:00,0.80

Until: 23:00,0.10

Until: 24:00,0.00

For: Sunday Holidays

Until: 8:00,0.00

Until: 13:00,0.10

Until: 22:00,0.70

Until: 23:00,0.20

Until: 24:00,0.00

For: SummerDesignDay

Until: 8:00,0.00

Until: 11:00,0.20

Until: 18:00,0.80

Until: 21:00,0.70

Until: 22:00,0.80

Until: 23:00,0.20

Until: 24:00,0.00

For: WinterDesignDay AllOtherDays

Until: 24:00,0.00

SCHEDULE:COMPACT

Sched_LtgAssembly

Fraction

Through: 12/31

For: Weekdays

Until: 6:00,0.05

Until: 9:00,0.40

Until: 22:00,0.75

Until: 23:00,0.25

Until: 24:00,0.05

For: Saturday

Until: 7:00,0.05

Until: 9:00,0.30

Until: 23:00,0.50

Until: 24:00,0.05

For: Sunday Holidays

Until: 7:00,0.05

Until: 12:00,0.30

Until: 22:00,0.65

Until: 24:00,0.05

For: SummerDesignDay

Until: 6:00,0.05

Until: 9:00,0.40

Until: 22:00,0.75

Until: 23:00,0.50

Until: 24:00,0.05

For: WinterDesignDay AllOtherDays

Until: 24:00,0.00

SCHEDULE:COMPACT

Sched_PlugsAssembly

Fraction

Through: 12/31

For: Weekdays

Until: 6:00,0.05

Until: 9:00,0.40

Until: 22:00,0.75

Until: 23:00,0.25

Until: 24:00,0.05

For: Saturday

Until: 7:00,0.05

Until: 9:00,0.30

Until: 23:00,0.50

Until: 24:00,0.05

For: Sunday Holidays

Until: 7:00,0.05

Until: 12:00,0.30

Until: 22:00,0.65

Until: 24:00,0.05

For: SummerDesignDay

Until: 6:00,0.05

Until: 9:00,0.40

Until: 22:00,0.75

Until: 23:00,0.50

Until: 24:00,0.05

For: WinterDesignDay AllOtherDays

Until: 24:00,0.00
On Tue, Jul 31, 2018 at 2:07 PM, my_sunny_night@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Hello All,

Is the internal heat gain from occupants taken into account for heating equipment sizing?

Thanks

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