Hot bypass gas can be:
- Directed to a waste heat boiler for steam or hot oil generation
- Blended with ambient air to the desired: Temperature, or Required oxygen content of other process combustion make up air
- Directed to a secondary air to liquid heat exchanger (or blended with ambient air to the most economical heat exchanger temperature)
When do you use hot gas bypass?
Hot gas bypass is recommended when the load on an evaporator varies and operation of the air conditioning system is desired at lower than design conditions. Additionally, hot gas bypass is used when the evaporator coil is designed for comfort cooling (latent and sensible loads) versus precision cooling (all sensible loading).
What is a mechanical hot gas bypass valve?
The mechanical hot gas bypass valve (HGB) is fed discharge gas (hot gas) teed off from the discharge line. The output of the valve is directly piped to the inlet of the evaporator after the TX valve.
What is a hot gas bypass on a dryer?
A hot gas bypass valve essentially allows you to keep your dryer running at its optimal temperature without risking the health of your system. Does gas bypass need to be hot? It’s possible to get both cold gas bypass valves and hot gas bypass valves.
What temperature should the thermocouple on a hot gas bypass be at?
As the suction pressure starts to fall below 58 psig, the hot gas bypass should start to modulate open to help stabilize the suction pressure at or just above 58 psig. At this point, the temperature reading at the thermocouple should start to increase. A reading of 120°F or higher should be observed.
What's the purpose of a hot gas bypass?
Hot gas bypass can stabilize the system balance point by diverting hot, high-pressure refrigerant vapor from the discharge line directly to the low- pressure side of the system. This tactic reliable operation by introducing problems stemming from insufficient oil return and refrigerant logging in the HGBP line.
Is hot gas reheat the same as hot gas bypass?
Advances in HVAC controls and technology in HVAC systems over the years has made hot gas reheat very popular. HOT GAS BYPASS provides an artificial load on the evaporator by introducing a portion of high pressure, high temperature gas to the evaporator/suction side of the system.
Does hot gas bypass dehumidify?
By using a hot coil, you wring the water out on the evaporator coil and then reheat the air on that second coil, providing neutral dry air. A lot of people think the hot-gas reheat dehumidifies but it's really the cooling coil doing the work.
How do you adjust a hot gas bypass?
HOT GAS BYPASS ADJUSTMENT By turning the adjustment stem one complete turn clockwise, the pressure setting will increase approximately 4 psig. By turning the adjustment stem counterclockwise one complete turn, the pressure setting will decrease approximately 4 psig.
Is an APR valve hot gas bypass?
The APR Control® is not “hot gas bypass”. “Other evaporator pressure control systems” would be referring directly to an evaporator pressure regulator valve (See Sporlan May 2007 / BULLETIN 90-20 page 3).
What is hot gas reheat HVAC?
The hot gas reheat feature is designed to control humidity at a specific level in the conditioned space. This is usually required when the outside temperature is cool and humid. It controls humidity without expending additional energy to reheat the cooled air.
Is hot gas reheat energy recovery?
Hot-gas reheat is a common type of heat recovery often employed in dedicated outside-air systems (DOAS).
How does hot gas defrost work?
The hot gas defrost process uses the superheated vapor from the compressor discharge (on high pressure and high temperature) as the heat source. This vapor is diverted on a third system line, bypassing the condenser and the expansion valve, and directed through the unit cooler coil, warming it from the inside.
How does a hot gas reheat coil work?
Hot gas reheat coils work by routing a portion of the gas that would go to the condenser in a standard system to a reheat coil. This coil then brings the air back up to a suitable temperature. Next, the air travels to a supply fan and then to the system's primary heating coil.
What is the effect of hot gas bypass method as a capacity control in compressor?
Hot gas bypass valves can be used in many different applications where the load on the evaporator varies, from residential, to server rooms, to process cooling equipment. Using a hot gas bypass valve can also prevent short cycling of a compressor and prevent evaporator freezing in low load conditions.
What is a hot pull down in HVAC?
WHAT IS A HOT PULL DOWN? “Hot pull down” refers to a condition in which the refrigerator has difficulty removing heat from the box. The phenomenon is due to the box having a much higher heat load than normal.
What does head pressure mean in HVAC?
Head pressure is the pressure generated by the gas compressor of your air conditioning system. This is something that we measure when we think that you might have a refrigerant problem. Head pressure that's within a reasonable range isn't a problem. It's high head pressure that's the issue.
Why use a hot gas bypass valve?
Using a hot gas bypass valve can also prevent short cycling of a compressor and prevent evaporator freezing in low load conditions. As a space or process temperature reaches set point, hot gas can be added to the evaporator to raise its temperature.
Why is a hot gas bypass valve false?
Because this load is not put there by heat from the return air, the load is referred to as false. Hot gas bypass valves can be used in many different applications where the load on the evaporator varies, from residential, to server rooms, to process cooling equipment. Using a hot gas bypass valve can also prevent short cycling ...
Why adjust a gas valve inwards?
Adjusting the valve inwards will allow more hot gas to flow through the valve, backing out the adjustment will allow less hot gas to flow through the valve. When setting up the valve, you may need to simulate a low load condition.
What is a hot gas bypass?
Hot gas bypass (also called discharge bypass) is a feature in a refrigeration system uses to satisfy the mechanical needs of the system during low load conditions. Low load conditions can lead to frosting or freezing the evaporator, refrigerant flood back to the compressor, system shutdown, oil return problems, and several other undesirable conditions.#N#The hot gas bypass utilizes a line from the discharge of the compressor to deliver high temperature, high pressure refrigerant either to the evaporator distributor (preferred) or the suction line to the compressor (which may overheat the compressor).#N#The components usually are a solenoid valve and a pressure/flow control. Larger systems will likely only have an automatic valve, but no solenoid valve. Below, is a system sketch of a basic discharge bypass line on a simple air-cooled system.
How does hot gas work?
Hot gas works by modifying two conditions in the evaporator, one, it raises the saturation pressure above freezing, and two, it displaces some liquid refrigerant that does the cooling.
What happens when discharge gas is injected in the suction line?
The effect is to remove gas that could pass through the condenser and evaporator then raise the back pressure to raise the over-all saturation temperature above freezing.
What is a hot gas bypass?
The hot gas bypass is a valve that automatically regulates the cooling temperature in the dryer exchanger based on the refrigerant pressure. The pressure measured after the heat exchanger directly correlates to the temperature in the system. A low pressure means there will be a low temperature. When a dryer is only partially loaded, there is ...
Why is it important to select a hot gas bypass valve?
It’s important to select a hot gas bypass that is able to fully open and close based on the pressure input. Hot gas bypass valves with limited opening capability are less likely to prevent freezing when the incoming load is especially low.
Table of Contents
What Is Hot Gas Bypass?
- Hot gas bypass, or HGBP for short, is essentially a valve that automatically regulates the cooling temperature in the refrigerant air dryer exchanger based on the pressure of the refrigerant. There is a direct correlation between the pressure measured in the heat exchanger and the temperature of the system, and so, if there is a low pressure there ...
What Is The Problem with Over-Cooling?
- The refrigeration circuit found within refrigerant dryers is sized to cool the full inlet capacity to a certain specified temperature. In the case that there is only a partial load on the dryer, the refrigerant is likely to over-cool the air which can become a serious problem. Over-cooled air will cause the water in the air to not just condense, but possibly even freeze. Now, water freezing wit…
Hot Gas Bypass Selection Considerations
- When selecting a hot gas bypass suitable for your refrigerant air dryer, it’s important to choose one that is capable of being fully open and closed based on the pressure input. Some people instantly go and purchase one without looking at the specifics, and in the case that you purchase a hot gas bypass valve that has limited opening capabilities, well, it’s less likely you will be able t…
FAQs
- If you have any questions regarding using hot gas bypass on refrigerant dryers, please leave a comment below, with a photo if applicable, so that someone can help you!