Single-Compressor Hot Gas Reheat HVAC for Stable Charge Balance
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Solution Overview
Problem
HVAC systems face challenges in maintaining a consistent refrigerant charge level and requiring additional equipment when using reheat heat exchangers for humidity control, leading to costly heating methods and difficulties in balancing refrigerant flow during both cooling and reheat modes.
Innovation Solution
The HVAC system employs a novel hot gas reheat configuration with a single compressor, two condensers, a reheat heat exchanger, and an evaporator, where refrigerant is split into two portions to allow balanced flow in both cooling and reheat modes, using a head pressure control device to maintain compressor discharge pressure and ensure sufficient refrigerant flow through the reheat heat exchanger.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a reheat heat exchanger is used to reheat air for dehumidification, then humidity control is improved, but refrigerant charge level becomes difficult to maintain and additional equipment is required
Solution Approach 1:
The first condenser is designed to serve dual functions: acting as a condenser during cooling mode and as a reheat heat exchanger during dehumidification mode. This multi-functionality eliminates the need for a separate reheat heat exchanger and additional equipment, while maintaining effective humidity control through the evaporator and reheat cycle
2Ease of operation
If electric or gas heat is used to reheat air, then dehumidification is achieved, but operational costs increase
Solution Approach 1:
The system uses itself to provide reheat functionality by directing refrigerant through the first condenser to heat the air after dehumidification. This self-service approach eliminates the need for separate electric or gas heating systems, significantly reducing operational heating costs while maintaining dehumidification capability
3Temperature
If refrigerant is circulated through a reheat heat exchanger, then air is reheated, but consistent refrigerant charge level cannot be maintained
Solution Approach 1:
The system dynamically switches the function of the first condenser between condensing mode and reheat mode based on operational requirements. During reheat mode, refrigerant flows through the first condenser to heat air, and the head pressure control device dynamically adjusts to maintain proper refrigerant charge levels, ensuring consistent temperature control without charge instability
4Ease of operation
If a second compressor is added to enable reheat mode, then dehumidification control is improved, but device complexity and cost increase
Solution Approach 1:
The single compressor is designed to operate effectively in both cooling mode and dehumidification/reheat mode by controlling refrigerant flow distribution. The compressor's suction and discharge connections are configured to work with the evaporator, first condenser (acting as reheat exchanger), and head pressure control device, eliminating the need for a second compressor while maintaining effective dehumidification control
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 configuration enables efficient dehumidification and heating without the need for additional equipment, maintaining balanced refrigerant flow and reducing operational costs by using a single compressor for both cooling and dehumidification control.
Implementation Method 1
The fluid flowing within the closed loop is generally formulated to undergo phase changes within the normal operating temperatures and pressures of the system so that considerable quantities of heat can be exchanged by virtue of the latent heat of vaporization of the fluid
Implementation Method 2
an evaporator where the fluid absorbs heat
Implementation Method 3
a condenser where the fluid releases heat
Implementation Method 4
the condensed refrigerant from the two condensers is then combined
Implementation Method 5
considerable quantities of heat can be exchanged by virtue of the latent heat of vaporization of the fluid
Implementation Method 6
using a head pressure control device to maintain compressor discharge pressure and ensure sufficient refrigerant flow through the reheat heat exchanger
Implementation Method 7
The air also can be reheated by passing the air over a reheat heat exchanger that circulates heated refrigerant from the closed loop of the HVAC system
Data Source
AI summary
The present disclosure is directed to a single compressor HVAC system with hot gas reheat. The system includes a single compressor, a pair of condensers, a reheat heat exchanger, an evaporator, and an expansion device. Within the system, the refrigerant exiting the compressor is separated into two portions. In the cooling mode, the first and second portions of the refrigerant are directed from the compressor through the two condensers in parallel. In the reheat mode, the first portion of the refrigerant is directed through the first condenser, while the second portion of the refrigerant is directed through the reheat heat exchanger. The system also may include a head pressure control device that is designed to maintain the compressor discharge pressure within a desired range by adjusting the condenser fan speed.