Terminal unit controls that handle both heating and cooling typically have multiple temperature set points. They typically have a cooling set point and a heating set point. The cooling set point is always equal to or greater than the heating setpoint. If the room temperature starts to rise above the cooling set point, the controller will provide additional cooling. If the room temperature drops below the cooling set point, the controller will maintain a minimum airflow limit in order to provide ventilation to the zone. If the room temperature drops below the heating set point, the controller will increase the airflow to move more air through a reheat coil and begin heating. The temperature range between the heating and cooling set points is referred to as the dead band. It is typically 2-4°F. This is the temperature range that the room temperature must pass through in order to switch from cooling to heating. For additional questions contact us at tu@titus-hvac.com.
If I’m understanding the question, there is no minimum airflow requirement for hot water coils. On a single duct VAV box with a hot water coil, there should be at least three airflow settings. The ‘maximum cooling’ needs to provide adequate cooling on a design day. Then the ‘minimum cooling’ needs to meet ASHRAE 62.1 ventilation requirements for a given space. Then you have a ‘heating’ flowrate. This is typically less than 50% of the ‘maximum cooling’ flowrate. It’s dependent on the amount of heat required in the space because heating delivered from overhead diffusers should never be more than 15°F higher than the room temperature setpoint. Here is the formula that relates air temperature rise to airflow: CFM = 927 * MBH/(LAT - EAT)
Thank you. To clarify, my question is about how to calculate heating CFM for a vav box with hot water coils instead of electric reheat. Thanks for your reply.
Can you explain me min cfm for 7 inch box size? v p =t.p - s.p v=4005*root of velocity pressure (assume 0.03) cfm= velocity * area just clarify me how do you get 70 for 7 inch...
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Wonderful tutorial!
Kindly explain heating, cooling and dead band setpoint.
Terminal unit controls that handle both heating and cooling typically have multiple temperature set points. They typically have a cooling set point and a heating set point. The cooling set point is always equal to or greater than the heating setpoint. If the room temperature starts to rise above the cooling set point, the controller will provide additional cooling. If the room temperature drops below the cooling set point, the controller will maintain a minimum airflow limit in order to provide ventilation to the zone. If the room temperature drops below the heating set point, the controller will increase the airflow to move more air through a reheat coil and begin heating. The temperature range between the heating and cooling set points is referred to as the dead band. It is typically 2-4°F. This is the temperature range that the room temperature must pass through in order to switch from cooling to heating. For additional questions contact us at tu@titus-hvac.com.
Please explain how to calculate minimum CFM for hot water coils
If I’m understanding the question, there is no minimum airflow requirement for hot water coils. On a single duct VAV box with a hot water coil, there should be at least three airflow settings. The ‘maximum cooling’ needs to provide adequate cooling on a design day. Then the ‘minimum cooling’ needs to meet ASHRAE 62.1 ventilation requirements for a given space. Then you have a ‘heating’ flowrate. This is typically less than 50% of the ‘maximum cooling’ flowrate. It’s dependent on the amount of heat required in the space because heating delivered from overhead diffusers should never be more than 15°F higher than the room temperature setpoint. Here is the formula that relates air temperature rise to airflow:
CFM = 927 * MBH/(LAT - EAT)
Thank you. To clarify, my question is about how to calculate heating CFM for a vav box with hot water coils instead of electric reheat. Thanks for your reply.
@@Suvi0999 Our previous response addresses your specific request
Can you explain me min cfm for 7 inch box size?
v p =t.p - s.p
v=4005*root of velocity pressure (assume 0.03)
cfm= velocity * area
just clarify me how do you get 70 for 7 inch...
7inch dia