CAV HVAC Control for Dehumidification and Discharge Air Temperature

Solution Overview

Problem

Constant Air Volume (CAV) HVAC systems face challenges in simultaneously managing dehumidification and discharge air temperature control functions, particularly in balancing latent and sensible cooling demands, which can lead to inefficient operation and humidity issues.

Innovation Solution

The implementation of an HVAC controller that receives both latent and sensible cooling demands and directs the operation of compressor and evaporator coils, along with reheat coils, to activate or deactivate them based on demand, ensuring optimal dehumidification and discharge air temperature control, using a processor to coordinate these functions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a CAV HVAC system employs a dehumidification function using reheat coils, then humidity control is improved, but discharge air temperature control becomes problematic

Engineering Contradiction:

Improvehumidity controlVSAvoiddischarge air temperature control

Core Design Contradiction:

Object-affected harmful factorsVSTemperature

Solution Approach 1:

The system dynamically switches between dehumidification mode and discharge air temperature control mode based on real-time sensor inputs. When humidity exceeds the setpoint, the reheat coils are activated for dehumidification; when humidity is acceptable, the system transitions to temperature control mode, dynamically adapting its operation to current conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The controller changes operational parameters by monitoring humidity levels and discharge air temperature, switching between different control modes. When relative humidity exceeds the setpoint, the system prioritizes dehumidification by activating reheat coils; when humidity is within range, it switches to maintaining discharge air temperature, changing the controlled parameter based on conditions.

Inventive Principle:

Principle #35Parameter changes

2Temperature

If a CAV HVAC system employs a discharge air temperature control function, then temperature control is improved, but dehumidification capability deteriorates

Engineering Contradiction:

Improvedischarge air temperature controlVSAvoiddehumidification capability

Core Design Contradiction:

TemperatureVSObject-affected harmful factors

Solution Approach 1:

The system uses feedback from both humidity sensors and temperature sensors to continuously monitor system performance. The controller compares actual humidity levels against the setpoint and activates dehumidification mode when needed, while also monitoring discharge air temperature to ensure temperature control requirements are met, using feedback from both parameters to guide operation.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system dynamically switches between dehumidification mode and discharge air temperature control mode based on real-time sensor inputs. When humidity exceeds the setpoint, the reheat coils are activated for dehumidification; when humidity is acceptable, the system transitions to temperature control mode, dynamically adapting its operation to current conditions.

Inventive Principle:

Principle #15Dynamics

3Adaptability or versatility

If a CAV HVAC system simultaneously processes latent and sensible cooling demands, then both dehumidification and temperature control are improved, but system complexity increases

Engineering Contradiction:

Improvesimultaneous latent and sensible coolingVSAvoidsystem operation complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The controller segments cooling demands into distinct latent (dehumidification) and sensible (temperature control) components. It processes these demands separately through dedicated control routines: one routine monitors humidity and controls reheat coils for dehumidification, while another monitors temperature and controls cooling for temperature maintenance, dividing the complex simultaneous control task into manageable segments.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system uses feedback from both humidity sensors and temperature sensors to continuously monitor system performance. The controller compares actual humidity levels against the setpoint and activates dehumidification mode when needed, while also monitoring discharge air temperature to ensure temperature control requirements are met, using feedback from both parameters to guide operation.

Inventive Principle:

Principle #23Feedback

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This solution allows for efficient balancing of cooling demands, improving the operation of CAV HVAC systems by effectively managing dehumidification and discharge air temperature control, enhancing the system's ability to meet both latent and sensible cooling requirements simultaneously.

Implementation Method 1

a latent cooling demand indicating a need for latent cooling of the air in the enclosure

Methodology Applied

Scientific EffectLatent cooling: Condensation

Implementation Method 2

a sensible cooling demand indicating a need for sensible cooling of the air in the enclosure

Methodology Applied

Scientific EffectSensible cooling: Heating

Data Source

PatentUS8255087B2Constant air volume HVAC system with a dehumidification function and discharge air temperature control, an HVAC controller therefor and a method of operation thereof

Publication Date: 2012.08.28 LENNOX IND INC

AI summary

An HVAC controller, a method of operating a constant air volume (CAV) HVAC unit and a CAV HVAC system are disclosed herein. In one embodiment, the HVAC controller includes: (1) an interface configured to receive both a latent cooling demand and a sensible cooling demand and (2) a processor configured to direct both a dehumidification function and a discharge air temperature control function for a CAV HVAC system employing the latent cooling demand and the sensible cooling demand.