Method and system for controlling fresh air ventilation of an air handling unit of an hvac system

Abstract

A current load on the AHU used to maintain one or more comfort conditions in the building space is determined, along with a remaining load capacity. A maximum additional fresh air ventilation air flow that could be admitted and conditioned using the remaining load capacity of the AHU such that the AHU could still maintain the one or more comfort conditions in the building space is determined. A fresh air intake damper position for the fresh air intake damper that increases the fresh air ventilation air flow through the fresh air intake damper by a fraction of the maximum additional fresh air ventilation air flow is determined. The fraction may be based at least in part on one or more of a temperature factor and an air quality factor. The fresh air intake damper is set to the determined fresh air intake damper position.

What is claimed is: 
     
         1 . A method for controlling a fresh air intake of an Air Handling Unit (AHU) of an HVAC (Heating, Ventilating and Air Conditioning) system servicing a building space of a building, the AHU including a fresh air intake damper for admitting a fresh air ventilation air flow, a return air duct for receiving return air from the building space, a mixed air duct for mixing the fresh air ventilation air flow from the fresh air intake damper and return air from the return air duct and providing a mixed air flow to a heating and/or cooling unit of the AHU which supplies a supply air flow to the building space, the AHU including a fan for providing a motive force to move the return air, the fresh air ventilation air flow, the mixed air flow and the supply air flow through the AHU, the AHU having a load capacity, the method comprising:
 determining a current load on the AHU that is used to maintain one or more comfort conditions in the building space;   determining a remaining load capacity of the AHU, wherein the remaining load capacity is the load capacity that is currently not being used to maintain the one or more comfort conditions in the building space;   determining a maximum additional fresh air ventilation air flow that could be admitted and conditioned using the remaining load capacity of the AHU such that the AHU could still maintain the one or more comfort conditions in the building space;   determining a fresh air intake damper position for the fresh air intake damper that increases the fresh air ventilation air flow through the fresh air intake damper by a fraction of the maximum additional fresh air ventilation air flow, wherein the fraction is based at least in part on one or more of a temperature factor and an air quality factor; and   setting the fresh air intake damper to the determined fresh air intake damper position.   
     
     
         2 . The method of  claim 1 , wherein the fraction is based at least in part on the temperature factor, wherein the temperature factor is dependent on a temperature difference between an outside air temperature, representative of a temperature of the fresh air ventilation air flow, and an inside air temperature, representative of a temperature of the return air. 
     
     
         3 . The method of  claim 2 , wherein the temperature factor is set to zero when the temperature difference is outside of a first predetermined temperature difference range. 
     
     
         4 . The method of  claim 2 , wherein the temperature factor is set to one when the temperature difference is within a second predetermined temperature difference range. 
     
     
         5 . The method of  claim 2 , wherein the temperature factor is scaled between zero and one based at least in part on the temperature difference when the temperature difference is within a third predetermined temperature difference range. 
     
     
         6 . The method of  claim 1 , wherein the fraction is based at least in part on an air quality factor, wherein the air quality factor is dependent on an air quality parameter that is representative of a measure of air quality in the building space. 
     
     
         7 . The method of  claim 6 , wherein the air quality factor is dependent on an urgency factor and a favorability factor, wherein:
 the urgency factor is dependent on a value of the air quality parameter along a predetermined air quality parameter value range; and   the favorability factor is dependent on a comparison between the air quality parameter that is representative of the measure of air quality in the building space with an air quality parameter that is representative of a measure of air quality outside of the building.   
     
     
         8 . The method of  claim 7 , wherein the air quality factor is dependent on the urgency factor multiplied by the favorability factor, wherein:
 the favorability factor is set to zero when the air quality parameter that is representative of the measure of air quality outside of the building is worse than the air quality parameter that is representative of the measure of air quality in the building space; and   the favorability factor is set to one when the air quality parameter that is representative of the measure air quality outside of the building is better than the air quality parameter that is representative of the measure of air quality in the building space.   
     
     
         9 . The method of  claim 1 , wherein the fraction is based at least in part on the temperature factor and the air quality factor, wherein:
 the temperature factor is dependent on a temperature difference between an outside air temperature, representative of a temperature of the fresh air ventilation air flow, and an inside air temperature, representative of a temperature of the return air; and   the air quality factor is dependent on an air quality parameter that is representative of a measure of air quality in the building space.   
     
     
         10 . The method of  claim 9 , wherein:
 the fraction is set to a first weighted sum of the temperature factor and the air quality factor using first weights when the temperature factor and/or the air quality factor meet one or more first predefined conditions; and   the fraction is set to a second weighted sum of the temperature factor and the air quality factor using second weights when the temperature factor and/or the air quality factor meet one or more second predefined conditions, wherein at least one of the second weights is different from at least one of the first weights.   
     
     
         11 . The method of  claim 1 , wherein the air quality factor is a maximum of a plurality of individual air quality factors, wherein each of the plurality of individual air quality factors relates to a different one of a plurality of air quality parameters. 
     
     
         12 . The method of  claim 11 , wherein the plurality of air quality parameters include two or more of CO 2 , PM2.5 and TVOC. 
     
     
         13 . The method of  claim 1 , wherein the fraction is based at least in part on two or more of a temperature factor, an air quality factor and a humidity factor. 
     
     
         14 . An Air Handling Unit (AHU) for servicing a building space of a building, the AHU comprising:
 a heating and/or cooling unit;   a fresh air intake damper for admitting a fresh air ventilation air flow;   a return air duct for receiving return air from the building space;   a mixed air duct for mixing the fresh air ventilation air flow from the fresh air intake damper and return air from the return air duct and providing a mixed air flow to the heating and/or cooling unit which supplies a supply air flow to the building space;   a fan for providing a motive force to move the return air, the fresh air ventilation air flow, the mixed air flow and the supply air flow through the AHU;   the AHU having a load capacity;   a controller, wherein the controller is configured to:
 determine a current load on the AHU that is used to maintain one or more comfort conditions in the building space; 
 determine a remaining load capacity of the AHU, wherein the remaining load capacity is the load capacity that is currently not being used to maintain the one or more comfort conditions in the building space; 
 determine a maximum additional fresh air ventilation air flow that could be admitted and conditioned using the remaining load capacity of the AHU such that the AHU could still maintain the one or more comfort conditions in the building space; 
 determine a fresh air intake damper position for the fresh air intake damper that increases the fresh air ventilation air flow through the fresh air intake damper by a fraction of the maximum additional fresh air ventilation air flow, wherein the fraction is based at least in part on one or more of a temperature factor and an air quality factor; and 
 setting the fresh air intake damper to the determined fresh air intake damper position. 
   
     
     
         15 . The AHU of  claim 14 , wherein the fraction is based at least in part on:
 the temperature factor, wherein the temperature factor is dependent on a temperature difference between an outside air temperature, representative of a temperature of the fresh air ventilation air flow, and an inside air temperature, representative of a temperature of the return air; and   the air quality factor, wherein the air quality factor is dependent on an air quality parameter that is representative of a measure of air quality in the building space.   
     
     
         16 . The AHU of  claim 15 , wherein:
 the fraction is set to a first weighted sum of the temperature factor and the air quality factor using first weights when the temperature factor and/or the air quality factor meet one or more first predefined conditions; and   the fraction is set to a second weighted sum of the temperature factor and the air quality factor using second weights when the temperature factor and/or the air quality factor meet one or more second predefined conditions, wherein at least one of the second weights is different from at least one of the first weights.   
     
     
         17 . The AHU of  claim 15 , wherein the air quality factor is dependent on an urgency factor and a favorability factor, wherein:
 the urgency factor is dependent on a value of the air quality parameter along a predetermined air quality parameter value range; and   the favorability factor is dependent on a comparison between the air quality parameter that is representative of the measure of air quality in the building space with an air quality parameter that is representative of a measure of air quality outside of the building.   
     
     
         18 . The AHU of  claim 17 , wherein the air quality factor is dependent on the urgency factor multiplied by the favorability factor, wherein:
 the favorability factor is set to zero when the air quality parameter that is representative of the measure of air quality outside of the building is worse than the air quality parameter that is representative of the measure of air quality in the building space; and   the favorability factor is set to one when the air quality parameter that is representative of the measure air quality outside of the building is better than the air quality parameter that is representative of the measure of air quality in the building space.   
     
     
         19 . A method for controlling a fresh air intake of an Air Handling Unit (AHU) of an HVAC (Heating, Ventilating and Air Conditioning) system servicing a building space of a building, the method comprising:
 estimating a minimum volume of fresh air that will need to be admitted by the AHU to maintain a predetermined air quality parameter below a threshold level in the building space over a predetermined time period into the future;   forecasting one or more outdoor conditions and one or more indoor conditions including temperature and air quality conditions over the predetermined time period into the future;   based on the forecasted one or more outdoor conditions and one or more indoor conditions, determining for each of a plurality of time intervals over the predetermined time period:
 a dilution factor that represents an estimated change in the predetermined air quality parameter in response to replacing a predetermined fraction of the air in the building space; 
 an energy factor that represents an estimated thermal energy required to condition the predetermined fraction of the air in the building space; 
 a cost/benefit factor that represents a ratio of the dilution factor and the energy factor; 
   assigning a portion of the estimated minimum volume of fresh air to each of the plurality of time intervals of the predetermined time period based at least in part on the cost/benefit factors so as to minimize a total energy consumption of the AHU over the predetermined time period into the future; and   during a first one of the plurality of time intervals, setting the fresh air intake of the Air Handling Unit (AHU) to admit the portion of the minimum volume of fresh air assigned to the first one of the plurality of time intervals.   
     
     
         20 . The method of  claim 19 , wherein after the first one of the plurality of time intervals, repeating the estimating, forecasting, determining, assigning and setting steps for the predetermined time period into the future but now starting at the end of the first one of the plurality of time intervals.