HVACR Temperature Control Basics
Summary
TLDRThe 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
🕒 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.
🌡️ 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.
Mindmap
Keywords
💡Time Control
💡Cam
💡Electronic Controllers
💡Programmable Logic Controller (PLC)
💡Thermal Output Modulation
💡Sensors
💡Deadband
💡Thermostat
💡Variable Speed Pump
💡HVAC Engineering
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
now to continue learning hvac
engineering as this is the end of this
video
don't forget to follow us on facebook
linkedin twitter instagram tick tock as
well as the engineering mindset dot com
Parcourir plus de vidéos associées
5.0 / 5 (0 votes)