RE: [EnergyPlus_Support] Cycling fans when spaces are unoccupied

Carolina,

CycleOnAny is what I normally use and seems appropriate for most buildings as long as the unoccupied setpoint is sufficiently different from the occupied setpoint.

Notice the “Thermostat Tolerance” and “Cycling Run Time” fields; these will affect how quickly the Manager starts the system and the minimum length of operation. If the Tolerance is too large, you may see “Unmet Load Hours”, and if the Run Time is too long ,the system will run unnecessarily.

I normally use 1C tolerance and 1800 seconds for Run Time.

That said, if you operate HVAC during unoccupied periods, the energy use will rise! The amount it rises is affected by the

· Occupied / Unoccupied Setpoint difference,

· Tolerance and

· Run Time settings.

With appropriate Output variables, you can study the performance during unoccupied periods to see if it is realistic and doing as you intend.

James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com

Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Carolina Galeazzi
Sent: Wednesday, August 22, 2012 3:30 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Cycling fans when spaces are unoccupied

Jim,

Shoul I use CycleOnAny on the AvailabilityManager:NightCycle? Is it normal that it increases the energy consumption in app 50%? This value doesn't seem correct to me, am I doing something wrong?

Thank you,

Carolina

De: Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Para: "EnergyPlus_Support@xxxxxxxxxxxxxxx" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Enviadas: Quinta-feira, 16 de Agosto de 2012 11:53
Assunto: RE: [EnergyPlus_Support] Cycling fans when spaces are unoccupied

Carolina,

Consider using the AvailabilityManager:NightCycle. If you specify constant fan operation during occupied hours, this manager will cycle the fan as needed during unoccupied hours.

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 Carolina Galeazzi
Sent: Thursday, August 16, 2012 10:51 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Cycling fans when spaces are unoccupied

Hi Richard,

Thank you for your answer.

So, the correct values for cycling fans in the fan operation mode schedule is:

0 (denotes cycling fan operation), used in unoccupied hours;

1 or other value other than 0 (denote continuos fan operation), specified for occupied hours.

Is this correct?

Carol

De: Richard Raustad <RRaustad@xxxxxxxxxxxx>
Para: EnergyPlus_Support@xxxxxxxxxxxxxxx
Enviadas: Quinta-feira, 16 de Agosto de 2012 11:26
Assunto: Re: [EnergyPlus_Support] Cycling fans when spaces are unoccupied

Just because you don't need to be bring OA in at night doesn't mean that you don't need to condition the zones, which means the supply fan must turn on.
During the day, the fan runs continuously to ensure the proper amount of OA, during the night, if there is a load, the fan turns on and off with the coils.

There is usually a fan operating mode schedule used with HVAC equipment that can cycle, or you can use a night ventilation manager to cycle the fan on for VAV systems.
OA control is independent of fan operation (i.e., you can have OA or not if the fan is running).

On 8/16/2012 10:12 AM, Carolina Galeazzi wrote:

Hi All,

To build an ASHRAE baseline model, it's said that 'supply and return fans should be cycled to meet heating and cooling loads during unoccupied hours'. I understand that fans should run for mechanical ventilation, but with zero outside airflow rate. How can I cycle the variable volume fan of the AHUs in Eplus, with zero outside airflow rate?
Thank you for your help!!
Carol

--

Richard A. Raustad

Senior Research Engineer

Florida Solar Energy Center

University of Central Florida

1679 Clearlake Road

Cocoa, FL  32922-5703

Phone:   (321) 638-1454

Fax:     (321) 638-1439 or 1010

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