How to Read Wiring Diagrams in HVAC Systems. There are various types of wiring diagrams used in the HVACR Industry. We’ll explain how to read a schematic wiring diagram and what the various symbols represent and how they function.
Wiring diagrams are used for the installation of the HVAC equipment, trouble shooting, or locating an electrical device in the control panel or within the unit. There are differences between the type of diagrams based on what they’re used for.
Schematic Wiring Diagram often called a Ladder Diagram and a Pictorial Diagram
The installation diagram will show those connection points most important for connecting the electrical power to the HVAC equipment, while the internal wiring diagrams are meant for troubleshooting by technicians. There is a pictorial diagram that gives a much more cluttered look at the electrical components and wiring as its intended to give you the proximity of the component within the unit.
HVAC Wiring Diagram and Legend
We’ll jump right into showing you a schematic diagram for a simple air conditioning unit.
We’ll make a ladder diagram using a simple air conditioner as our example. First we have the main electrical supply lines L1 and L2 providing 208/230 volt, single phase power. Then we’ll need a transformer to provide 24 volt low voltage power for our thermostat, switches and relays. Next we add a thermostat to control the air conditioner, and we connect the power from the low voltage side of the transformer to the “R” terminal of the thermostat.
We’ll need to add an indoor fan motor connection to the line voltage side of the diagram and provide contacts for turning on and off the fan. Next we add the refrigerant compressor to the line voltage side and include contacts and a run capacitor.
To complete our refrigerant circuit we need to add an outdoor condenser fan motor on the line voltage side of the diagram. This provides us with the three largest energy consuming devices in our air conditioner, the compressor, condenser fan and indoor fan motors.
Wiring Diagram showing Electrical Relay Coil on low Voltage side Controlling contacts on the line voltage side.
Now we need to add some way to control these three motors, which we’ll do from the low voltage side and the use of the thermostat. First we’ll add a compressor relay on the low voltage side of the wiring diagram. This relay will communicate with the compressors contactors on the line voltage side of the wiring diagram as required to start and stop the compressor.
Also included are some safety devices to protect the compressor from high and low pressure conditions. There is a High Pressure Switch that will shut off the compressor if the pressure in the refrigerant system gets too high. Likewise there is a low pressure switch that will shut off the compressor if the pressure in the refrigerant system gets too low. These safety devices do this by cutting off the low voltage power to the relay coil, which in turn opens the contacts on the line voltage wiring feeding the compressor and outdoor fan. We need to do the same thing for the indoor fan, so we’ll add a relay coil that will open and close a set of contacts on the line voltage side that feeds the indoor fan motor.
Looking at the thermostat we can see that if we move the fan switch to “Auto” then the thermostat will cycle on and off the compressor and indoor fan motor. If we put the fan switch to “On” then low voltage power is always provided to the indoor fan relay, which means that the fan will run all the time, even when the compressor is off.
Let’s look at how the symbols on the diagram relate to actual physical, real world items. This is what an electrical relay might look like without it’s protective cover. We have two relays in our diagram, the Compressor and Indoor Fan Relays. The relay has two main parts, the coil, which is located on the low voltage side of the diagram, and the contacts, which are located on the line voltage side.
When the thermostat is on, low voltage power will be running through its wires energizing the coils of the relays for the indoor fan and compressor. The relay coil will cause the contacts to close which allows line voltage power to energize the compressor, condenser fan and indoor fan motors. When the thermostat is off the coil is de-energized and the contacts open, turning off the compressor and fans. Again, if we energize the coil the contacts close to start the compressor and fans.
We have the pictorial wiring diagram and the schematic wiring diagram. The schematic wiring diagram is also known as a ladder diagram. This is due to its arrangement of vertical lines on each side of horizontal lines which are comprised of electrical components.
This is a pictorial representation of what the electrical components look like when looking directly at the internal control board. This lets you see where the parts are located, but it’s not as useful for troubleshooting as the schematic ladder wiring diagram we just looked at. The relays are shown as blocks just as the transformers are. This allows us to easily find them within the HVAC equipment, but doesn’t give us a good way of troubleshooting a problem.
Schematic Diagram
The service technician needs to be able to read the wiring diagrams in order to troubleshoot problems. The quickest and less cluttered diagram is the schematic diagram, which shows system functionality without the clutter. The schematic diagram is designed in a ladder format, where line voltage L1 and L2 are shown as vertical lines, and all the electrical components shown on horizontal lines. The lines represent electrical wires while the various symbols are used to represent electrical components, from relays and contacts, to transformers, motors and compressors. There should be a legend that identifies what each symbol represents.
How to read wiring diagrams. Ladder Wiring Diagram / Schematic Wiring Diagram
There are symbols for the various types of switches including thermostats and pressure limiting devices. There are symbols for Relays and their corresponding contacts that energize or de-energize circuits. The contacts are shown on the diagram as they would be normally without any electrical power being supplied. You can see that all of our example contacts are what is called normally open, meaning with no power they are set to be open. When a contact is open, no electrical power can flow through it.
Electrical circuits can flow in series which means there is only one path for electricity to flow or they can be parallel circuits which allow multiple paths for the electricity.
Once the technician has reviewed the schematic wiring diagram and has a suspicion of the part causing the problem, the pictorial diagram can be referenced to see where that part is located in the unit.
By looking at the schematic wiring diagram the technicians can see how the piece of equipment should be operating by following the modes of operation. If the controller calls for cooling or heating, they should be able to see how the schematic diagram components will be activated to bring on and off the system, along with safety devices that protect the equipment. The schematic diagram allows for a quick view of how the system should operate and allows for troubleshooting any problems.
The technician will find the wiring diagrams attached to an access panel, electrical cover or housed within a internal pocket.
How Heat Transfer Works. There are three basic methods by which heat transfers to and from objects. We’ll explain these three methods and how they’re used in the heating and cooling loads for the sizing of air conditioners and how heat is transferred to and from humans. The heat is measured in BTU’s or Joule.
If you prefer to watch the Video of this presentation, then scroll to the bottom or click on this link. How Heat Transfer Works.
According to the second law of thermodynamics, heat moves from a warmer object to a cooler one. This is how heat uses any of the three methods to move from the outdoors to the indoor environment, or to and from our bodies. We’ll explain the three methods of heat transfer using conduction, radiation and convection, and a fourth one for humans called perspiration.
Three Methods of Heat Transfer
No matter whether you’re at home or in the office, the methods of heat transfer are the same.
How Heat Transfer Works using Radiation, Conductance and Convection
Conduction
Conduction is the easiest to understand because as a child you were told not to touch the stove or other hot surfaces or you’ll get burned. You’ll feel the heat transfer when you grab the hot metal handle of a pot on the stove, or touch an object that has been sitting in the hot rays of the sun. This is where heat is transferred by one object coming in contact with another, a direct object to object transfer.
Conduction occurs when heat is passed from one molecule to another in a chain reaction through an object. When heat is added to an object, its molecules speed up as does its temperature. These heated molecules bump into the adjacent molecules causes their velocity to increase and to heat up. This change reaction keeps occurring as long as heat is added or as long as there is an imbalance between molecules. This is most notable when heat is applied to a metal object that you come into contact with.
Three Methods of Heat Transfer – Radiant, Conductance and Convection
Conduction occurs constantly in the home or office when the outdoor temperature surrounding the walls, windows and roof is different than the indoor temperature. The heat will move through the construction materials at a rate defined by the resistance or “R” value of the material, the total square feet, and the temperature difference between outdoors and indoors. Q = A x U x Delta-T. The “U” value is the inverse of the total resistance of the wall or roof assembly.
The higher the “R” value the less the rate of heat transfer. This is how insulation reduces the heat transfer rate, while metals are highly conductive materials and easily move heat through them.
Three common methods of Heat Transfer include Radiation, Conductance and Convection
Radiation
Radiation occurs when the sun’s rays travel through space and strikes an object. That object absorbs the heat and can pass the heat along using any of the other heat transfer processes. This is one method by which heat gain occurs in buildings as it falls upon the structure and through windows.
If you have felt the warmth of a concrete or asphalt sidewalk or street after the sun went down or was blocked by clouds, this would be by conductance as the surface you touch is warm or the warm surface transfer its heat to the air that comes in contact with the surface. You could also feel the heat emanating from the surface as convection, as the air is warmed surrounding the surface and rises upward.
Radiant Heater as used in a Warehouse. The walls, floors and Objects in room that are in the path with absorb radiant heat
This is the same method by which infrared radiant heaters work. They radiate heat through the space until they land on an object that absorbs the heat, which could be a concrete floor in a manufacturing facility or someone working. The heat that hits the floor can than move through the concrete floor by conductance while also emanating upward in the air stream by convection. The walls, floors and ceiling can then radiate this heat back out to objects and the people surrounding the space.
Using the stove as our example again, we would feel the heat radiating out from the hot burner without actually having to touch it. Radiation acts like a waveform, emanating from a warm object to another object without effecting the space in-between. The walls, floors and ceiling can then radiate this heat back out to objects and the people surrounding the space.
To block infrared radiation from coming through windows there are now low-e coatings that can be installed that blocks infraredradiation.
Convection
Convection is the process of heat being dissipated by air motion. As hot air rises off the surfaces of walls it causes air motion that has an effect on human comfort. Heat is transferred from one area to another by the movement or flow of air, which is basically the movement of molecules. Since hot air naturally rises it will cause any heat in the space to be carried by air streams upward.
Air Conditioners and Heat Pumps
The heat that finds its way into your home or office is absorbed by the refrigeration system in your air conditioner or chilled water in some commercial buildings. The warm air is circulated over a refrigerant or chilled water coil where the heat is absorbed into the medium. See our video in the Refrigerant Cycle 101.
The Human Body and the Effects of Heat
The human body can give up heat through the three methods of heat transfer previously discussed, including a fourth one of perspiration.
Convection occurs when air moves across your body picking up body heat if the air is cooler. This causes the warmer air to rise, inducing cooler air to take its place. The faster the air moves the greater the cooling effect.
Radiation occurs when objects surrounding you are warmer than you are. This causes the object to radiate heat across the space between the object and you. By increasing the heat removal rate with ventilation, the cooler the object will become around you. When you are warmer than the surrounding objects, you’ll radiate heat out from your body.
Perspiration is one of the benefits of the human body as it facilitates the cooling of the body. As moisture evaporates from the skin it cools down the body while removing heat. When air blows across the body while perspiring the effects of evaporation is increased, providing an increased cooling effect.
How Heat Transfer Works – Radiation, Conduction and Convection
6 Steps for Designing HVAC DDC Controls. In this article we’ll cover the six basic steps to designing a DDC controls system. By following these six steps you’ll get a basic understanding of what it takes for a control engineer to design a basic controls system. Then, we’ll explain the various types of points and controllers that are used in our example.
At the heart of a properly operating HVAC system is the layer of controls that keep the system operating as intended. If the controls aren’t functioning properly then there will be a loss of occupant comfort and an increase in energy consumption. The controls must be designed to work with the HVAC system.
Let’s start by making a list of the equipment we’ll need for our HVAC design.
Step #1 List all Systems to be Controlled
First make a list of all the systems that will need to be controlled. This could include the heating hot water plant, chilled water plant, air handlers, fan coils and VAV boxes. For our example we’ll use a Heating Hot Water boiler system. The example we’ll use will be from the perspective of the boiler’s controller.
List of all Systems to be Controlled by the DDC System
Step #2 – Make a Schematic Controls Diagram
From your list of systems you can make a simple controls diagram. Draw the equipment for your system on a piece of paper or into your computer program. Arrange the equipment starting with the source, such as a boiler or chiller. Then put any pumps, VFD’s, control valves and sensors that might be required.
Schematic DDC Controls Diagram
Here we show a boiler, it’s associated heating hot water pump, Variable Frequency Drive (VFD), a 3-way control valve and a Differential pressure transmitter (DPT), and a Heating Hot Water Supply Temperature Sensor. These are the basic components for our system.
Step #3 – Identify Points on the Control Diagram
The sequence of operation will identify points of control that will need some form of connection to a controller.
There are four basic points that are used in DDC control diagrams.
#1 Analog Outputs (AO) – Modulate a damper or valve through a range of flow. The control signal is usually sent as a 0-10 VDC or 4-20 milliamp electrical signal to the device to be controlled. Since this is too small of an electrical signal to operate a damper or a control valve, there will be a transducer that converts the analog signal to a higher electrical power to operate the device. The diagram shows we have an analog output to 3-way control valve and the variable frequency drive.
DDC Control Diagram with Input and Output Points Shown
#2 Analog Inputs (AI) – A range of values from Input sensors for items such as temperature, pressure, CO2, and humidity. The analog signal coming from the device will be converted to a digital signal within the controller so it can be processed by the computer. We have two analog inputs in our diagram, a temperature sensor and the differential pressure transmitter.
#3 Binary Outputs (BO) – Often a simple command to enable a piece of equipment to start or for opening a damper or valve. Also known as Digital Outputs (DO). In our diagram we have two binary outputs for starting the boiler and pump.
#4 Binary Inputs (BI) – Used to retrieve the operating status of a piece of equipment. This notifies the controller if a certain piece of equipment is running. Also known as Digital Inputs (DI). The diagram shows two binary inputs for the confirmation that the boiler and pump are running.
HVAC DDC Controller for a Heating Hot Water Boiler System
Step #4 – List the Sequence & Modes of Operation
Describe what occurs to the system and equipment during occupied and unoccupied modes. Indicate whether a piece of equipment is started or stopped, such as turning on and off a boiler, or whether the item needs to create an alarm for failure.
Using the sequence of operation we’ll expand the modes of operation to include trigger points for the system or piece of equipment. This could be temperatures, pressures, alarms and various differential temperature and pressure ranges. The sequence of operation is a very important part of the controls design as it informs the system operator how the system will operate to achieve the design goals.
This is like the verbal commands you receive when using a GPS guided map in your car. It’s step by step instructions on what needs to be done to achieve the design intent. The setpoints are clearly stated along with how they are determined, while each variable is controlled by a single control loop.
The sequence will define how each device is controlled in the various modes of operation, such as normal operation, occupied or unoccupied mode, shut down mode, and alarm mode if required. Its normal mode of operation should be stated clearly.
Control engineers have saved templates of various sequences of operation that they can use or modify to fit the requirements of any project.
Here is what a sequence of operation might look like for our Heating Hot Water system.
Sequence of Operation for Heating Hot Water System
Sequence of Operation for a DDC Controls System
DDC Controller shall start boiler when Heating Hot Water Pump is verified to be running.
Hot Water boiler “ON” status to be confirmed, or an alarm is activated.
As the heating hot water piping pressure differential decreases, pump speed will increase. As the HHW piping differential pressure increases, pump speed will decrease.
DDC Controller will modulate the pump speed with a 4-20 milliamp signal to the variable frequency drive based on differential pressure.
DDC Controller shall reset heating hot water temperature based on outside air temperature reset schedule (Hot water temperature = 180°F at 0°F outside air temperature, hot water temperature = 120°F at 60°F outside air temperature).
This of course is a very simple explanation of the sequence of operation. The actual sequence will involve more descriptive details, but this gives you an idea of how they are generated. One item not discussed is scheduling, which includes what happens in occupied and unoccupied modes.
Step #5 – Make a Controls Points List
This is a simple chart that shows all the control points for the equipment and system. Points provide data for use in controlling the environment and can be used in software calculations or computer logic. Points provide the controller with information on the temperature, pressure, carbon monoxide level, humidity, the quantity of air or water flowing in a system, including other data inputs, along with output command signals.
HVAC DDC Controls Points List
There are points that are considered hardware and provide data to a controller or receive data from the controller, and then there are software points or virtual points that are housed within the control logic. We’ll cover the hardware points for a Heating Hot Water System containing a single boiler.
The first column is a description of the point. The following columns will be the various types of points that maybe required for any of the points described. There are analog and digital inputs and outputs, alarms, and other points. A number value indicates that the point is required. The control point can be an input sensor or the output control for the modulation of a damper or control valve.
Large systems will require a lot of points, while a smaller system will require much less. The more points the more cost associated with furnishing and installing the controls system. The points list gives a quick overview of just how many points are involved with the system.
Each point will need to be hardwired or configured wirelessly into the system or equipment controller. The controller allows various input and output points to be connected.
In a plans and specification project you’ll find the points list and the sequence of operations on the drawings or in the specifications. A clearly written and accurate points list and sequence of operation will provide the installing contractor with a clear roadmap to achieve the engineer’s requirements.
Let’s look at the first two columns which are the inputs.
Looking at our example we see a binary output signal to enable or turn on the boiler. Next we see a binary input using a current transmitter to see if the power is flowing to the boiler. Next we have a binary output signal to turn on the pump through the VFD, while there is a analog output to control the speed of the pump using a differential pressure sensor. Once again we use a current transmitter to confirm that a piece of equipment is running, in this case the pump.
Supply water temperature sensor which requires an analog input from the sensor to the controller. There is an analog input for the differential pressure sensor which gives an indication of the pressure difference between the supply and return water piping. This will help control the VFD speed. If the pressure increases in the system, then the VFD will slow down the pump motor.
Also, on the list of points we see the boiler status requirement which involves a digital input. This can be done with a simple current transmitter that is connected to the boiler which shows current flow when in operation.
Remember that analog points provide for a range of measurements or control variability, while a digital point is two states, either on/off, start/stop or similar.
A digital input device could be a flow switch that will indicate whether the fan is blowing air or is off. It could also be a current device that detects the flow of electricity, which would then make a contact to indicate that the motor is running. Another device is the pressure sensor which is a digital input point that informs the controller that there is pressure in the system caused by the fan blowing air. All these devices are examples of digital input points for the purpose of obtaining the status of a piece of equipment.
Next, we’ll look at the two columns of outputs. Analog outputs would direct devices to modulate like that of a control valve or damper, while digital output devices could start or stop a piece of equipment.
A digital output signal is sent to the VFD enabling the pump motor to run, while the analog output signal to the VFD will adjust its speed. The points list also shows that we want a digital output to operate the turning on and off the boiler.
There is a column for alarms that need to be generated to alert the facility staff of a problem or for alarm tracking. There is a column to indicate if the item described needs to be added to the front-end graphical display. The column identified as Software points can be used for in-direct points that transmit data on the network for use by other controllers. This allows sharing of any analog, digital or logic accumulated on this system.
There is an extra column for other devices or points that are not tied into the controller but may need to be considered to have a functional system. These could include safety devices, like high-limit switches that protect the system but are not part of the input or output of the controller. Some valves or dampers don’t require a controller to operate as they can just require an on/off position which can be done with a thermostat or safety limit switch.
The points list could indicate the total amount of points that are currently designed into the system, but you’ll find that most engineering firms don’t show this on their drawings. This is something that they use behind the scenes to keep track of how many inputs and output ports have been assigned on the controller. The controller has a limited number of inputs and outputs, so it’s important to know how many have been used, and how many remain. The engineer may specify that there are to be so many spare spots on the controller for future expansion.
Step #6 – Write Controls Specifications
Another step after the fifth, would be the design of the overall system architecture and for the controls engineer to write the controls specification, but that is beyond the scope of this article.
Looking at our points list for our boiler system controller we can see all the input and output devices that need to be connected to the controller.
Controllers
Controllers can be provided with the equipment or added on by the control’s contractor. This takes coordination between the installing HVAC contractor who is responsible for buying the major HVAC equipment and the controls contractor. They can be the same company if the HVAC contractor has their own controls division.
Controllers are like small computers that can be made specifically for a piece of equipment or system function. They are designed in all sizes with varying numbers of inputs and outputs. Small systems require a small number of inputs and outputs, while large system can be comprised of many inputs and outputs along with sub-networks of other controllers. The controller requires input signals in order to make decisions on output signals. For hazardous areas where an explosion could occur from a digital controller, there are pneumatic controllers that can be used, or with some additional money the electronic ones can be made explosion proof.
Controllers have various analog and digital input and output connections that allow for the normal points required for that piece of equipment. There are also universal controllers that allow any connection to accept either analog or digital points of connection. The controllers will be located throughout the facility to operate the various pieces of equipment and systems. The controllers will be connected with communication cable into a network that provides the facility operator with an overview of the total system.
These controllers are configurable to allow programmers to set parameters that match the design requirements. The code can be customized for various setpoints (temperature, carbon monoxide levels, pressure, humidity), time schedules, alarms, trending, timers, and logic.
HVAC DDC Controls System with Frontend
The points list will identify all the input and outputs for each of the controllers. Each controller has its own input and output devices, specifically designed for the application. These controllers have onboard logic that processes the input data and responds as programmed to control field devices. These controllers can also communicate with an automation layer controller using BACnet or other protocols.
We covered the 6 Steps for Designing HVAC DDC Controls. While these are the basic steps as we have defined them, control engineers will have various methods of their own. Either way, the end game is the same, a Complete Functioning HVAC Controls Systems.
5 Practical Home Plumbing Upgrades to Help Conserve Water and Energy. Water and energy conservation is a priority in many households, and plumbing upgrades are one of the most effective ways to help achieve this goal. Many options are available to help reduce water usage, but some upgrades are more effective than others.
This blog post will explore the top plumbing upgrades that can help you save water and energy. We’ll look at the benefits of each upgrade and discuss how they can help you meet your water and energy conservation goals. So, let’s get started!
1. Dual Flush Toilets
The technology behind dual flush toilets is based on a simple concept. When the user pushes the button, a diverter in the tank opens to allow the water to flow into the bowl. The type of flush depends on the size of the opening. A full flush opens up a larger opening for more water, while a half flush opens a smaller opening for less water.
These toilets come in various designs and colors, making them easy to fit into any bathroom decor. They are also available in standard and elongated models, so you can choose the one that works best for your space. Additionally, these toilets use less water per flush, so you don’t need to think of high water bills.
The installation of a dual-flush toilet is relatively simple and should be done by a professional plumber. This will give you peace of mind knowing that your new toilet is installed properly and meets all local plumbing codes. Once installed, you’ll enjoy the benefits of a dual-flush toilet for years.
2. Low-Flow Faucets and Showerheads
Low-flow fixtures are often equipped with aerators that mix air with water, creating a mist-like spray. This spray is sufficient for everyday uses like washing hands or dishes and helps conserve more water than a traditional fixture.
Low-flow fixtures can also be equipped with pressure-compensating devices that maintain a consistent flow rate regardless of the incoming water pressure. This ensures that the water used remains consistent even if your home’s water pressure changes.
Choose Low Flow Fixtures to save water
A low-flow faucet or showerhead, for instance, can help you save anywhere from 10-15% in water usage, depending on what type of device you choose.
3. Greywater Systems
Two types of greywater systems are available: point-of-use (POU) and whole-house systems. POU systems use a pump and filter to collect greywater from one or two fixtures, such as a bathroom sink or shower.
Whole-house systems capture all of the greywaters from the house, treating and storing them for future use. Depending on the size of your home and the type of system you choose, installation costs can start from a few hundred dollars up to several thousand.
Overall, greywater systems are an excellent way to help conserve water in your home. They are a cost-effective and efficient way to reduce water usage while helping you save money on utility bills.
When choosing a greywater system, select one certified for safe use, as some systems can be hazardous if not properly maintained. Also, check with your local authorities, as regulations for greywater systems vary by state. If done correctly, a greywater system can be a great way to conserve water in your home!
4. Low-Flow Toilets
Low-flow toilets are one of the most popular plumbing upgrades for conserving water. These toilets are designed to reduce the amount of water used with each flush, using around 1.6 gallons of water in every flush, unlike traditional toilets, which can use up to 3.5 gallons per flush. This makes low-flow toilets a great option for saving on water bills and reducing water waste, and they are usually quite affordable, too.
Choose Low Flow Fixtures to save water
5. Tankless Water Heaters
Modern tankless water heaters have features that will ensure that you’re only heating water when needed, helping save even more water in the long run.
Some models come equipped with features that allow users to set their desired water temperature, which helps ensure that only the necessary amount of water is heated instead of wasting hot water that isn’t being used. Others come with recirculating pumps installed so that hot water reaches your fixtures quicker than usual. This means less water is wasted while waiting for hot water to reach the faucet or shower head.
However, installing a tankless water heater may be challenging. Water heater installation should include proper measurements to ensure the toilet fits comfortably in the available space.
During a water heater installation, professional plumbers can check for any potential plumbing problems that may cause leaks or other plumbing issues down the road. They also check the connections between the tank and bowl of the new dual-flush toilet to ensure everything fits properly and maximizes water conservation.
Save Water and Energy with These Plumbing Upgrades
Making eco-friendly home improvements can greatly lower your water and energy usage, saving you money and helping the environment simultaneously. If you’re looking to reduce your water and energy consumption, plumbing upgrades are one of the best places to start.
