OpenStudio - EEMs 1: Demand Controlled Ventilation (DCV)

In this episode, we discuss how to simulate one of the easiest Energy Efficiency Measures (EEMs); Demand Controlled Ventilation (DCV). DCV varies the amount of outdoor air based on the actual number of occupants in the spaces. Airflow rates are calculated proportionally using the sum of the zone level outdoor air requirements or using the ASHRAE 62.1 Ventilation Rate Procedure. Not covered in this video: More advanced versions of this measure can modulate the outdoor airflow rates based on Indoor Air Quality (IAQ) measured by Carbon Dioxide levels or other indoor contaminants. See this episode for a measure that automates this: https://youtu.be/Q-LLPsZun3Y Transcript: Hi all we are back with another episode. In this episode we are going to discuss one of the simplest Energy Efficiency Measures to implement in OpenStudio: Demand Controlled Ventilation. We have a simple rest stop restroom building. Go to our HVAC systems Tab. Add a simple rooftop air loop system. This system does not have cooling...we will delete the cooling off of it. Assign all of the zones in the building to this one HVAC system. We do have an outside air system and it looks like this default system is hard sized with zero minimum outdoor air flow rate... That would not be applicable to this scenario because we do have some area minimum flow rates required for the spaces. Let us put this to autosized. I can just show you that real quick... If we go to space types you will see if we just select the restroom, the design specification outdoor air you will see that we have 7 CFM/person. We also have an air outdoor air flow rate of 0.02 CFM/SquareFoot. This is probably too low. We will use 0.06 CFM/SquareFoot. Let us go back to the air loop system. Select the air loop itself. Scroll down to see how the system outdoor air is being calculated. For this scenario it is very simple. We can just use Zone Sum. The other options are the ASHRAE standard 62.1 ventilation rate procedures; those take into account the ventilation effectiveness of the system and the primary air flows in the zones. That is how the outdoor air gets proportioned to the multizone system. This example system is already simple so we can just leave it as the simplified ZoneSum method. Run the simulation. This will be our baseline, without demand controlled ventilation. We will save this as a different file..."WithDCVimplemented". The question is: How do you implement demand control ventilation? Go back to the Air Loop. Select the Air Loop system. Click the control button up at the top. Turn on demand controlled ventilation. Now, press the simulate button. It has finished successfully. Go to the Results Summary tab. Let us go back to the other one...this is the Baseline (without demand controlled ventilation). We will open this one first. Open up DView. Let us take a look at the outdoor air mass flow rate. You can see it is constant throughout the year. So, this system runs 24/7 and provides a constant outdoor air flow. Let us take a look at the one with the demand controlled ventilation implemented. Again, we will open up DView. Select outdoor air mass flow rate. This one is a little bit different. You can see that it fluctuates. We can zoom into somewhere. In February. February 9th. Also for this one; February 9th. This is the Baseline; without DCV. This is the one with demand controlled ventilation. You can see the Baseline provides a constant outdoor air flow rate. With demand controlled ventilation you can see. When there are fewer people in the building it modulates down to the minimum air flow rate. As more and more people come into the building, it increases that airflow. As people leave the building, the outdoor air flow rate requirement goes down and so it provides less outdoor air. So, it is as simple as that. However, there are more complications involved with this. It depends on how complex your models are. There are some things to keep in mind. This DCV is basically doing exactly what I just said. It is counting the number of people that are coming into the building and as it adds more people, more ventilation air is required. The ventilation air is calculated based on the design specification outdoor air requirement per person. Here we have about 7 cubic feet per minute per person. It counts the number of people in the building. It totals up the required airflow. We can take a look at the occupancy schedule for the building. You can see this is the number of people in the building, throughout the day. Early in the morning there are very few people in the building. Then, it increases. Then it decreases. You can see this looks very similar to the profile for outdoor air. The more people that come into the building, the more outdoor air flow is required. ... Complete transcript: https: //www.helix-engineers.net/technical-articles