Evaporator Coil! How it Works- Refrigerant Flow, Phase Change, Saturation Point, Superheat, Tips!

Summary

In this educational video, the presenter from A/C Service Tech explains the function of a vertical evaporator coil in an HVAC system. The script covers the process of air movement, the role of the thermostatic expansion valve in controlling refrigerant flow, and the importance of maintaining superheat to ensure efficient operation. It also discusses potential issues like insufficient airflow and coil freezing, emphasizing the need for proper system maintenance and correct air flow settings.

Takeaways

• 🌀 The evaporator coil is a crucial component of an air conditioning system, functioning to absorb heat and maintain temperature within a building.
• 💧 The coil operates by attracting humidity to its fins, which then drips into a condensate pan and is drained away.
• 📍 The coil can be configured for vertical or downflow operation, depending on how air is directed through it.
• 🔄 High-pressure, high-temperature liquid refrigerant enters the evaporator coil through the liquid line and is regulated by a thermostatic expansion valve (TXV).
• 🌡 The TXV controls the refrigerant flow, ensuring a balance of 20% flash gas and 80% liquid, which is crucial for efficient heat absorption.
• 🔆 As the refrigerant travels through the coil, it absorbs heat, transitioning from a liquid state to a saturated state and eventually to vapor.
• ♨️ The top part of the coil is where the refrigerant turns into complete vapor and begins to superheat, increasing in temperature above the saturation point.
• 🛠 Insufficient airflow across the coil can lead to issues such as freezing, highlighting the importance of proper air circulation for coil performance.
• 🔍 To ensure optimal performance, it's essential to check for adequate air flow, clean filters, and appropriate settings for the blower motor.
• ⚖️ The thermostatic expansion valve plays a key role in maintaining a superheat of 14 degrees, which is vital for the system's efficiency and proper refrigerant charging.

Q & A

What is the primary function of an evaporator coil?

The primary function of an evaporator coil is to absorb heat from within the building, maintaining the desired temperature by cooling the air that passes over it.

How does the air flow direction vary in a vertical evaporator coil?

In a vertical evaporator coil, the air can flow in from the bottom and come out through the sides and the top, or it can be used as a downflow where air comes down, passes through the coil, and goes out beneath.

What happens to the humidity when it comes into contact with the evaporator coil?

The humidity gets attracted to the fins of the evaporator coil and then drips down into the condensate pan.

What are the two main lines that supply the evaporator coil with refrigerant?

The two main lines that supply the evaporator coil with refrigerant are the suction line and the liquid line.

What is the role of the thermostatic expansion valve in the evaporator coil?

The thermostatic expansion valve controls the flow of high-pressure, high-temperature liquid refrigerant into the evaporator coil, ensuring it turns into a mixture of 20% flash gas and 80% liquid.

How does the refrigerant change as it moves through the evaporator coil?

As the refrigerant moves through the evaporator coil, it absorbs heat, transitioning from a liquid state to a saturated state, and finally turning into a complete vapor.

What is superheat and why is it important in the evaporator coil?

Superheat is the temperature increase above the saturation point after the refrigerant has turned into a vapor. It is important because it indicates the efficiency of the refrigerant's heat absorption and helps maintain the proper functioning of the HVAC system.

How does the thermostatic expansion valve maintain superheat?

The thermostatic expansion valve maintains superheat by regulating the amount of refrigerant entering the coil, aiming to keep a consistent 14 degrees of superheat.

What should be checked before assessing the refrigerant charge in an evaporator coil?

Before assessing the refrigerant charge, one should check that the air filter is clean, there is good airflow from the registers, and the blower motor is set to the capacity that matches the TXV and outdoor condensing unit.

What happens if there is not enough airflow across the evaporator coil?

If there is not enough airflow across the evaporator coil, it can start to freeze as it won't be able to absorb heat effectively, leading to a continuous drop in temperature until it turns into an ice cube.

How does the size of the blower motor affect the airflow across the evaporator coil?

The size of the blower motor affects the airflow across the evaporator coil by determining the CFM (cubic feet per minute) value. A larger blower motor can provide more airflow, which may require adjusting the airflow to match the capacity of the TXV and outdoor condenser.

Outlines

00:00

🌀 Understanding the Evaporator Coil

The paragraph explains the function of an evaporator coil in an air conditioning system. It describes a vertical evaporator coil where air enters at the bottom and exits through the sides and top. The process involves the absorption of humidity by the coil's fins, leading to condensation and dripping into a pan. The refrigerant enters as a high-pressure, high-temperature liquid and passes through a thermostatic expansion valve (TXV), which regulates its flow. The refrigerant then travels through the coil, absorbing heat and transitioning from a liquid to a vapor state. The goal is to achieve a superheat, which is the temperature increase above the saturation point, before the vapor returns to the compressor. The importance of proper airflow across the coil is emphasized to prevent freezing and ensure efficient heat absorption.

05:03

🔧 Ensuring Proper Airflow and System Sizing

This paragraph focuses on the importance of adequate airflow across the evaporator coil to maintain system efficiency. It discusses how to match the blower motor's capacity with the coil and outdoor condenser unit's requirements. The speaker advises setting the blower motor to the highest fan speed for optimal airflow. The paragraph also touches on the concept of adjusting the airflow based on the size of the furnace and blower motor, ensuring that the system operates at the correct capacity. The speaker concludes by encouraging viewers to check their air filters and register outputs for good airflow and to ensure the blower motor is set appropriately for the system's specifications.

Keywords

💡Evaporator Coil

An evaporator coil is a key component in air conditioning and refrigeration systems. It is responsible for absorbing heat from the air, which cools the space. In the video, the service tech explains that the coil operates by having air blow through it, with the humidity being attracted to the fins and then dripping into a condensate pan. The coil's operation is central to the video's theme of understanding how an evaporator coil functions.

💡Thermostat Expansion Valve (TXV)

The thermostatic expansion valve is a device that controls the flow of refrigerant into the evaporator coil. It ensures that the correct amount of refrigerant is fed into the system to maintain optimal cooling. The video mentions that the TXV turns high-pressure, high-temperature liquid refrigerant into a mix of 20% flash gas and 80% liquid, which is crucial for the coil's performance.

💡Suction Line

The suction line is the pathway through which the refrigerant vapor returns to the compressor after it has absorbed heat in the evaporator coil. It plays a vital role in the refrigeration cycle, as explained in the video, where the vapor, after being superheated, travels back to the compressor via the suction line.

💡Superheat

Superheat refers to the temperature increase of the refrigerant vapor above the saturation point after it has turned into a vapor in the evaporator coil. The video emphasizes the importance of maintaining a certain degree of superheat, which is typically around 14 degrees, to ensure the system operates efficiently. The superheat is measured at the evaporator coil's outlet.

💡Airflow

Airflow is critical for the proper functioning of the evaporator coil. The video script mentions that if there is not enough airflow across the coil, it can lead to inefficiencies and even freezing of the coil. The speaker advises checking for adequate airflow by ensuring a clean filter and proper operation of the blower motor.

💡Condensate Pan

The condensate pan is a container located at the bottom of the evaporator coil where the condensed moisture, attracted to the coil's fins, collects and is drained away. It is an essential part of the system to prevent water damage and maintain hygiene, as highlighted in the video.

💡Refrigerant

Refrigerant is the substance that circulates through the air conditioning system, absorbing and releasing heat to cool the space. The video describes how the refrigerant changes state from liquid to vapor and back again, which is fundamental to the cooling process.

💡Metering Device

A metering device, such as the thermostatic expansion valve discussed in the video, regulates the flow of refrigerant into the evaporator coil. It is crucial for controlling the amount of refrigerant that enters the coil, ensuring optimal performance and preventing issues like overcharging or undercharging.

💡Blower Motor

The blower motor is the component that drives the airflow through the evaporator coil. The video script explains the importance of setting the blower motor to the correct capacity to ensure adequate airflow across the coil, which is vital for the coil's ability to absorb heat and maintain temperature.

💡Downflow

Downflow refers to the direction of air movement in certain evaporator coil configurations, where air enters at the top and exits at the bottom. This term is used in the video to describe one of the possible orientations of the evaporator coil, which affects how air is circulated and cooled.

💡Fins

Fins are the thin, closely spaced metal plates on the evaporator coil that increase the surface area for heat transfer. In the video, the service tech explains that humidity is attracted to these fins, which helps in the condensation process. The design of the fins is crucial for the efficiency of the evaporator coil.

Highlights

Introduction to how an evaporator coil functions.

Description of a vertical evaporator coil and its airflow pattern.

Explanation of humidity attraction to the coil fins and condensate drainage.

Detailed process of refrigerant flow through the evaporator coil.

Functioning of the thermostatic expansion valve in the refrigerant cycle.

Conversion of high-pressure liquid refrigerant into a mixture of flash gas and liquid.

Heat absorption process in the evaporator coil.

Concept of saturation in the refrigerant cycle.

Importance of achieving superheat in the refrigerant cycle.

Role of the thermostatic expansion valve in maintaining superheat.

Impact of insufficient airflow on the evaporator coil's performance.

Potential for coil freezing due to inadequate heat absorption.

Importance of checking air filters and airflow before assessing refrigerant charge.

Guidance on matching blower motor capacity with the outdoor condensing unit.

Explanation of how to adjust blower motor settings for optimal airflow.

Conclusion and invitation to the next video on the e service tech channel.

Transcripts

[Music]

[Music]

hey guys this is ac service tech and

today I want to go over how an

evaporator coil functions all right so

this one's a vertical evaporator coil

all right so the air blows in the bottom

and comes out through the sides and the

top or it could also be used as a down

flow where the air comes down has to

come through the coil and go out down

through uh beneath what happens is um

the actual humidity gets attracted to

these fins and then it just drips right

down into the condensate pan take your

uh drain down from the lowest most spot

anyway um so how this thing works all

right um You have your suction line and

your your liquid line all right so your

liquid line comes in high pressure high

temperature liquid refrigerant comes in

hits the metering device which in this

case is a thermostatic expansion valve

all right and it turns into um 20% flash

gas and 80% liquid then it comes into

the bottom of the evaporator coil all

right as a 20% flash gas 80% liquid and

it comes up to say the midpoint all that

time it's absorbing heat all right so I

would say like say we can split this up

into thirds and say that this bottom

part is mainly liquid okay this middle

part is completely saturated okay

saturated means it's liquid and Vapor

both exist at the same time okay then

you can say that basically the top third

or so is where you should be turning

into a complete vapor and from there on

it's increasing in temperature after

it's turned into a vapor okay so the

vapor is actually getting super heated

the temperature increase above the

saturation point

that's when it comes back out and it

comes through the suction line back to

the compressor again all right so that's

how it works so it's absorbing heat from

within the building as it's absorbing

heat all right it's a the evaporator

coil is actually able to maintain

temperature all right and uh if you do

not have enough air flow across the

evaporator coil so say your outdoor

condensing unit was a four ton and the

thermostatic expansion valve was a four

ton it's going to be feeding to much

refrigerant into uh the coil all right

and it's just not going to be able to

ABS um be able to absorb as much heat as

it's capable of all right but the

biggest thing is you want to make sure

that you have a super heat and that's

where the thermostatic expansion valve

comes into play all right so um

thermostatic expansion valve actually

has a little bit more play as far as the

refrigerant charge goes um because it's

always trying to maintain 14 degrees of

superheat all right so it reads the

pressure right here okay and then you

have a bulb which is actually also

reading the pressure attached onto the

suction line all right so um

basically this whole process right here

is the low pressure side after it gets

to here this is high pressure high

temperature liquid refrigerant hitting

the metering device turning into a 20%

flash gas 80% liquid for say the first

third it's absorbing heat and turning

more and more into a saturated state I

would say maybe roughly right around the

middle would be where it's almost like

5050 50% liquid 50% Vapor until it comes

all the way to the point where there's

barely any liquid left and it's all

vapor and then from there on it gets

superheated and the temperature increase

and vapor form is where it comes out at

this is the superheat if you were to

have a a this would be out of the

evaporator coil box and if you were to

have a access port here at a temperature

probe that would be reading your

superheat what we're normally reading

all the way back at the condensing unit

or the heat pump that is the total

superheat so if there's anything that's

any temperature that's gained or lost in

the suction line um that's why it's

included in the total superheat but

that's what we normally use for charging

units that have Pistons instead of txvs

all right uh but we use subcooling back

at the condensing unit to measure for uh

our charging procedure for this system

right here if you do not have enough air

flow across this Quil the Quil is going

to start to freeze all right um it's not

going to have it's it's not going to be

able to actually um absorb any heat and

so the temperatur is just going to

continue to get lower and lower and

lower until the thing turns into an ice

cube all right so things to check for

before checking a charge make sure that

your filter is clean make sure you have

good air coming out of the registers the

blower motor set to the capacity that

this TXV and the outdoor condensing unit

are so say the uh furnace was a 042

which is a 42,000 BTU blower and this

was a um 42 let's say 3 and A2 ton TXV

and a 3 and2 ton outdoor condenser then

that um you want to have it its highest

fan speed which would be the black all

right so for a psse motor be black for

variable speed you got to set the dip

switches inside the unit all right to

get the maximum amount of air flow

across this coil um if you had a furnace

that was larger and it had a 060 blower

that would be 60,000 BTUs 12,000 BTUs

per ton and say this was still that 3

and2 ton capacity then then you could

say you could kick down that that uh CFM

uh cubic feet per minute value to

something that's closer uh to 3 and half

tons all right so I hope that helps and

I hope you enjoyed yourself we'll see

you next time at e service tech

Channel