HVACR Temperature Control Basics

Summary

The video script discusses time control systems and their evolution from mechanical to electronic, offering greater functionality and ease of use. It explains how these systems can be programmed for specific schedules, optimizing energy use in buildings. The script further delves into the use of sensors, both digital and analog, for accurate temperature and pressure readings. It highlights the importance of modulating thermal output for maintaining desired temperatures within a deadband, using examples of thermostatic radiator valves and motorized valves. The video also touches on the challenges of controlling multiple units with a single pump and the solution of using a pressure sensor and variable speed pump to maintain consistent pressure and flow rate.

Takeaways

• 🕒 Time control systems regulate the operation of devices at specific times and durations.
• 🔧 Traditional mechanical timers have been largely replaced by electronic controllers with more functions and flexibility.
• 🏢 Advanced systems use an optimizer and programmable logic controllers (PLCs) to efficiently manage heating in large buildings based on occupancy schedules and outdoor temperatures.
• 🌡️ Modulation of thermal output is more effective than simple on/off control for maintaining desired room temperatures.
• 📊 A thermostat compares room temperature to the set point and adjusts the heating system accordingly.
• 🔄 Digital sensors provide binary on/off information, while analog sensors offer a range of values for precise measurements.
• 🔧 Deadband conditions are set to prevent unnecessary fluctuations in temperature, maintaining a stable environment.
• 💧 Special valves, like motorized valves and thermostatic radiator valves, can modulate the thermal output of heating systems.
• 🔄 Variable speed pumps maintain constant pressure and flow rate in heating systems with multiple radiators or fan coil units.
• 📚 Understanding HVAC engineering involves learning about the operation and integration of various components like sensors, valves, and controllers.

Q & A

What is the primary function of time control in systems and components?

The primary function of time control is to manage the operation of systems and components by turning them on and off at specific times and for certain durations, which can be useful for maintaining comfort and efficiency in various settings.

How has the technology of timers evolved from the past to the present?

Timers have evolved from being mechanical devices that used cams to control the opening and closing of contacts, to modern electronic controllers that are compact, easier to use, and offer more functions, such as seven-day schedules and multiple on-off times per day.

What is the role of a relay in electronic timers?

Relays are used in electronic timers to open and close circuits, allowing for the control of electrical devices and systems according to the set schedule.

How does a programmable logic controller (PLC) optimize heating systems in large buildings?

A PLC checks the clock to determine if heating should be turned on, considers the scheduled occupancy time, current room temperature, desired temperature, and outdoor temperature to calculate the necessary start time and heat output for efficient and comfortable heating.

What is the purpose of modulating the thermal output in a heating system?

Modulating the thermal output allows for better temperature regulation by increasing or decreasing the temperature to match the actual load, ensuring energy efficiency and maintaining a comfortable environment.

What are the two main types of sensors used in heating systems, and how do they differ?

The two main types of sensors are digital and analog. Digital sensors can only detect on/off states, while analog sensors provide a range of values, allowing for more precise measurements such as exact temperature or pressure.

How does a thermostatic radiator valve work in a heating system?

A thermostatic radiator valve uses a chamber filled with a wax-like substance that expands and contracts with room temperature changes, controlling the valve position and adjusting the heat output of the radiator to match the room's demand.

What is the significance of a deadband condition in temperature control?

A deadband condition, typically set at plus or minus one degree Celsius from the required temperature, helps to alleviate temperature swings by turning the heating on and off within a small range around the desired temperature, maintaining comfort and efficiency.

What issue arises when using a fixed speed pump with multiple radiators or fan coil units?

When using a fixed speed pump, closing one valve can cause a pressure increase in the pipework, leading to increased flow rate through other valves. This can disrupt the system's control and cause the valves to constantly adjust, potentially leading to faster breakdowns.

How can a variable speed pump help in maintaining a constant flow rate through radiators?

A variable speed pump adjusts its speed in response to changes in valve positions, working to maintain a constant pressure and flow rate through the radiators, regardless of when other valves open or close.

What additional features do modern electronic controllers offer for temperature regulation?

Modern electronic controllers offer features such as programmable schedules, the ability to set different on-off times per day, and integration with other systems like PLCs for more sophisticated temperature and energy management in buildings.

Outlines

00:00

🕒 Time Control Systems and Their Applications

This paragraph discusses the concept of time control in systems and components, allowing them to operate at specific times and durations. It explains how time controls can be used to manage heating systems, such as turning on the heating before waking up to ensure a warm house. The evolution from mechanical to electronic timers is highlighted, with electronic controllers offering more functions and flexibility, including seven-day schedules and multiple on/off times. The paragraph also delves into the use of relays in electronic timers and the integration of programmable logic controllers in sophisticated systems for large buildings, emphasizing the optimization of heating based on occupancy, room temperature, and outdoor conditions.

05:01

🌡️ Modulating Thermal Output for Efficient Temperature Control

The second paragraph focuses on the limitations of on/off control for maintaining desired temperatures and introduces the concept of modulating thermal output. It explains how a simple heating system with a thermostat and a motorized valve can adjust the temperature to match the actual load. The paragraph discusses the use of sensors, both digital and analog, for precise temperature or pressure measurements. It also covers the concept of deadband, which helps stabilize temperature swings by setting a range around the desired temperature. The challenges of controlling multiple radiators or fan coil units with a single heating source are addressed, along with solutions like thermostatic radiator valves and variable speed pumps to maintain constant pressure and flow rate.

Keywords

💡Time Control

Time Control refers to the mechanism that allows systems and components to operate at scheduled times. It is crucial for managing heating systems, for instance, to ensure that a house is warm before occupancy. The script mentions using a cam to physically push contacts together to complete a circuit, as well as electronic controllers for more complex scheduling and optimization.

💡Cam

A cam is a mechanical component used in simple time controls to push contacts together and complete a circuit. As the time dial rotates, it forces the cam to open and close the contacts, thereby controlling the operation of devices like heating systems.

💡Electronic Controllers

Electronic Controllers are modern devices that have replaced mechanical timers. They are compact, user-friendly, and offer more functionality, including multi-day schedules and multiple on/off times per day. These controllers use electronic relays to manage circuits and are typically programmable for enhanced control over systems.

💡Programmable Logic Controller (PLC)

A Programmable Logic Controller (PLC) is a sophisticated system used in larger buildings for advanced control. It interfaces with an optimizer to check the clock, determine occupancy times, and adjust the heating schedule accordingly. PLCs can also calculate the required start time based on the current and desired temperatures, as well as outdoor conditions.

💡Thermal Output Modulation

Thermal Output Modulation is the process of adjusting the heat output of a system to match the actual load or demand. Instead of simply turning a system on or off, modulation allows for fine-tuning the heat output to maintain a desired temperature within a certain range, improving energy efficiency and comfort.

💡Sensors

Sensors are devices that detect and respond to physical stimuli such as temperature, pressure, or light. In the context of the video, there are two main types: digital and analog. Digital sensors provide binary on/off information, while analog sensors offer a range of values, allowing for precise measurements.

💡Deadband

Deadband is a range of temperature around a set point within which a system will not activate heating or cooling. This concept is used to prevent unnecessary cycling of the HVAC system and to maintain a stable, comfortable temperature by allowing small fluctuations without triggering the system.

💡Thermostat

A thermostat is a device that measures and maintains the temperature within a system. It compares the actual temperature to the desired set point and adjusts the system accordingly. In heating systems, a thermostat can control the position of a damper in a fan coil unit or a motorized valve in a radiator to regulate heat output.

💡Variable Speed Pump

A variable speed pump is a pump that can adjust its operating speed to maintain a constant pressure and flow rate in a system, regardless of changes in demand. This technology is used in heating systems to counteract the pressure changes caused by the operation of multiple thermostatic radiator valves, ensuring efficient and stable operation.

💡HVAC Engineering

HVAC Engineering is the branch of engineering that deals with the design, installation, and maintenance of heating, ventilation, and air conditioning systems. It involves understanding the principles of thermal comfort, energy efficiency, and system control to create comfortable and sustainable indoor environments.

Highlights

Time control systems regulate the operation of devices based on set schedules, ensuring optimal use of resources.

Mechanical timers have evolved into electronic timers that use relays to manage circuits, offering more functionality and ease of use.

Electronic controllers often include a seven-day schedule with multiple on/off times, catering to varying daily requirements.

Sophisticated systems use an optimizer and programmable logic controllers (PLCs) to calculate the most efficient heating times based on occupancy and outdoor temperatures.

Modulating thermal output by adjusting temperatures can better match the actual load demand, as opposed to simple on/off control.

The use of thermostats allows for the comparison of room temperature with a desired set point, enabling precise control over heating systems.

Digital sensors provide binary on/off information, whereas analog sensors offer a range of values for more detailed system feedback.

The thermostat can be located on the output device or remotely, controlling the position of a damper in a fan coil unit for temperature regulation.

Deadband conditions are set to minimize temperature swings, maintaining a comfortable and energy-efficient environment.

The deadband value is determined by various factors and often found through trial and error to achieve optimal comfort and efficiency.

Special valves can modulate thermal output, maintaining temperature within a set deadband for better climate control.

In heating systems, the use of a motorized valve can reduce the gas supply to match the heat output to the room's requirements.

Multiple radiators or fan coil units connected to a single heating source require individual control to maintain consistent temperatures.

The thermostatic radiator valve automatically adjusts its position based on temperature changes, matching the heat output to room demand.

A motorized valve controlled by a room thermostat can vary the flow rate of hot or cold water, adjusting the thermal output of a unit.

The use of a pressure sensor and a variable speed pump can maintain constant pressure and flow rate in a system with multiple valves, enhancing control and longevity.

Variable speed drives and pumps work together to maintain consistent performance in heating and cooling systems, regardless of valve adjustments.

Transcripts

time control allows systems and

components to turn on and off at certain

times as well as for certain durations

of time or we can delay something

turning on or off for a certain amount

of time

for example on a cold morning we want

the heating to turn on before we wake up

so that the house is nice and warm a

simple time control uses a cam to push

contacts together and complete a circuit

as the time dial rotates it will force

the cam to open and close the contacts

to turn the heating on and off

timers used to all be mechanical however

these days timers are usually electronic

and typically use relays to open and

close circuits

by the way we have covered how relays

work in detail previously i'll leave a

link for you in the video description

down below

electronic controllers are compact and

much easier to use

they have far more functions but usually

at least a seven day time schedule with

multiple on off times per day

this is useful for example in a small

office which is closed on weekends so

during the winter the heating is

scheduled to turn off on weekends

and then it starts slightly earlier on a

monday morning

because it will take longer to warm the

building up

a more sophisticated system typically

used in much larger buildings will use

an optimizer and for this example we

have it connected to a programmable

logic controller this will check with

the clock should the heating turn on

today and if so at what time will the

building be occupied the clock replies

yes the scheduled occupancy time is nine

am

the plc checks the current temperature

of the room and calculates the

difference between this temperature and

the desired temperature

it then checks the outdoor temperature

to calculate how long it will take to

heat the building

because on a cold day it will take

longer so it will need to start earlier

turning systems or components on and off

to regulate the room temperature does

work but not very well

instead we can modulate the thermal

output by increasing and decreasing the

temperature to match the actual load

for example in this simple heating

system we have a thermostat in the room

to measure the temperature and then a

controller will compare this to the

desired set point temperature and decide

if the room is too hot too cold or just

right

if it is too cold or too hot then the

controller alters the position of the

motorized valve to increase or decrease

the amount of hot water entering the

radiator

we have two main types of sensors

digital and analog

digital inputs can only tell if

something is on or off nothing in

between for example an on off switch or

a bimetallic strip

the circuit is either open or closed

so we can only tell if the temperature

is above or below a certain temperature

analog inputs vary their signal

they might vary in resistance voltage or

current between a minimum and maximum

value

so we can use these to determine the

exact temperature or pressure

we have covered how temperature sensors

work previously and i'll leave a link

for you in the video description down

below

the thermostat could be located on the

output device like a thermostatic

radiator valve or remotely like a room

thermostat which controls the position

of a damper in a fan coil unit

to alleviate swings in temperature we

set a deadband condition

typically plus or minus one degree

celsius from the required temperature

for example if we want a room

temperature of 21 degrees celsius with a

dead band of plus or minus 1 degree

the heating will turn on when the room

temperature falls below 20 degrees

celsius

and it will then switch off when it is

above 22 degrees celsius

this gives us an average temperature of

21 degrees celsius

the deadband values depends on many

factors it can be modeled on a computer

but generally it is found through trial

and error

with small incremental changes to find

the optimal point where the room is

comfortable and the system operates

efficiently

on and off control makes it difficult to

maintain a desired temperature

instead we can use special valves to

modulate the thermal output

keeping the temperature within a certain

deadband

in a simple heating system when the gas

boiler turns on it will run at full

power to heat the water

but then it reduces the gas supply by

using a motorized valve

this reduces the heat output of the

boiler it does this instead of turning

it off the water temperature set point

is kept in the dead band so the heat

output is equal to the heat leaking out

of the room

most systems have a single heating or

cooling source with multiple radiators

or fan core units connected to this

these are usually in different rooms so

we need to control the output of the

individual units

the simplest method to achieve this is

the thermostatic radiator valve

this is a valve found on heated water

systems

it basically uses a chamber filled with

a wax liquid or gas which expands and

contracts as the room temperature

changes

this controls the valve position the

hotter it gets the further it closes the

valve the colder it gets the more it

opens the valve the heat output of the

radiator therefore matches the demand of

the room

alternatively a radiator or fan call

unit could use a motorized valve which

is controlled by thermostat in the room

this will vary the flow rate of hot or

cold water into the unit

this will vary the thermal output of the

unit to match the demand however

if a fixed speed pump supplies multiple

units

then as one valve closes it causes a

pressure increase in the pipe work so

the flow rate of water increases through

the other valves that's a problem

because it will increase the heat output

the valves will constantly adjust to try

and maintain the correct temperature

we will therefore lose control of the

system and as the valves are working so

much they will break down much faster

to overcome this we could install a

pressure sensor and a variable speed

pump

as the valve opens and closes the pump

changes speed to try and maintain a

constant pressure and thus a constant

flow rate through the radiators

this happens regardless of when another

valve opens or closes

we have covered how variable speed

drives work and also how pumps work in

our previous videos do check those out

i'll leave a link for you in the video

description down below

check out one of the videos on screen

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engineering as this is the end of this

video

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