Re: [EnergyPlus_Support] Hybrid Ventilation Control

Hi,

Thank you Lixing, Richard, Linda and Fabio for your concern and support

I've looked through the detailed report variables as recommended

It was very helpful to understand more the performance of the system and the control logic

Through different timesteps in an hour, the hybrid status is alternating from 1 (allowing natural ventilation) to 2 (mechanical ventilation) according to the cooling setpoint temperature (CSP) and the cooling demand. Once the air temperature reached the CSP (27C), the mechanical cooling system is operating in order to keep the air temperature just below the CSP while the supplied fresh air exceeds the minimum requirements (no problem).

My problem summarizes in that, after several timesteps of HVAC operation, the hybrid status changes to 1 as the outdoor temperature (30C) is between the min.& max. values (15-35C) while natural ventilation is not permitted as the outdoor temperature is higher than the indoor temperature (27C). At these moments, the airflow is below the minimum ventilation rate. Accordingly, the hourly supplied amount of fresh air (by both HVAC and Natural Ventilation) doesn't match the minimum requirements which affect the Indoor Air Quality.

Since the ventilation rate due to natural ventilation is below the minimum requirements at the critical moments, the system should then switch to mechanical ventilation with minimum ventilation rate to maintain acceptable Indoor Air Quality. Therefore, a combined control mode will be helpful at these circumstances, am I right?

Another alternative could solve the problem by matching the maximum outdoor temperature with the CSP but we can only specify just one max. outdoor temp. for the whole year. In that case, Which value could be used when we use different seasonal/monthly CSP (which is my situtation as well)?

I appreciate very much your help

Kind regards,

Sherif

From: Lixing Gu <gu@xxxxxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Wednesday, May 6, 2009 8:47:23 PM
Subject: Re: [EnergyPlus_Support] Hybrid Ventilation Control

Sherif:

I think Rich answers your question regarding the hybrid status value between 1 and 2. I am trying to clarify the control logic. When the control mode is temperature, the control will check whether the outdoor temperature is between min and max temperature specified in the inputs, such as 15 and 35C you mentioned. If it OK, the control also check whether HVAC system is required to turn on or not, by checking indoor temperature. For example, if the indoor temperature in the controlled zone is above the cooling setpoint. HVAC system turns on.

The control mode 4 is only working with the AirflowNetwork model. If the infiltration by opening windows is above the scheduled input. HVAC system turns off and windows are open, regardless of other conditions.

Hope this helps.

Lixing

----- Original Message -----

From: Sherif Ezzeldin

To: EnergyPlus_Support@ yahoogroups. com

Sent: Wednesday, May 06, 2009 11:40 AM

Subject: Re: [EnergyPlus_ Support] Hybrid Ventilation Control

Lixing,

Thanks for your concern

The main concern is designing an acceptable indoor environment is to maintain both Thermal Comfort and Indoor Air Quality requirements.

Concerning Indoor Air Quality requirements, a minimum ventilation rate (10l/s/person= 1.29ACH) is required to maintain acceptable level of CO2 in an office space. A successful hybrid design should provide that ventilation rate by natural ventilation and switch to mechanical ventilation just when the minimum value couldn't be met.

At the same time, the zone operative temperature should lie within the upper & lower thermal comfort boundaries. A successful hybrid design should maintain natural ventilation as long as the zone operative temperature is within the comfort boundaries, once it reaches the upper comfort boundary temperature (cooling setpoint temperature CSP), the system should switch to mechanical cooling

In EnergyPlus, if I set the control mode to 1 (temperature) and the min. and max. outdoor temp. to 15C and 35C as in the example file, when the outdoor temp. reaches 32C and the indoor temp is 28C and the CSP is 26C , in that case the mechanical system should operate and the hybrid status should be equal to 2 but the hybrid status value is between 1 and 2. My explanation could be that since the outside lies between 15C and 35C, then hybrid control allows natural ventilation, and since the outdoor temp is higher than the indoor temp, then natural ventilation is not allowed.

Alternatively, if I set the control mode to 4 (Ventilation rate), the system just compare the predicted ventilation rate with the minimum value regardless to the cooling setpoint, therefore, during summer, the indoor temperature exceeds the upper comfort boundary temperature but with acceptable ventilation rate.

Could you please help me may be there is something I miss-understood?

Kind regards,

Sherif

From: Lixing Gu <gu@xxxxxxxx. edu>
To: EnergyPlus_Support@ yahoogroups. com
Sent: Wednesday, May 6, 2009 2:24:48 PM
Subject: Re: [EnergyPlus_ Support] Hybrid Ventilation Control

Sherif:

The existing EnergyPlus only allows one of controls at the same time. Any combination is not allowed. Could you provide your control in detail, so that possible enhancement will be considered?

Thanks.

Lixing

----- Original Message -----

From: Sherif Ezzeldin

To: EnergyPlus_Support@ yahoogroups. com

Sent: Wednesday, May 06, 2009 6:26 AM

Subject: [EnergyPlus_ Support] Hybrid Ventilation Control

Hi,

I'm trying to improve the performance of a hybrid ventilation scheme in an office space

I'm using EnergyPlus version 2.2

Concerning the control mode in the "Hybrid Ventilation control" model, we have to specify either to control natural and mechanical ventilation by temperature (control mode=1) or by ventilation rate (control mode=4)

Is there a way to combine these two control modes together and to let the program first to calculate the temperature (compare it with the acceptable temperature ranges) and the ventilation rate (compare it with the minimum ventilation rate) all together and then decide whether to provide natural or mechanical ventilation?

Thanks for your support

Kind regards,

Sherif