Mechanical rooms have very important equipment that needs to be protected. Often mechanical rooms are not conditioned and subject to outside temperatures and freezing conditions that can freeze piping inside the mechanical. For that reason mechanical rooms often have unit heaters located there to protect piping and other things that cannot be frozen or subject to freezing conditions. The components and sequence of operation are fairly simple. The main components in a hot water unit heater include a fan, a valve, and of course the piping and coils along with the cabinet.
Hot Water Unit Heater Sequence of Operation
Each Hot Water Unit Heater shall be controlled by a unit mounted thermostat. Sometimes this will refer to as a wall mounted thermostat. Upon a drop in space temperature below the heating set point of 55° F the fan shall start and the hot water valve shall open. When the temperature rises above the set point, the fan shall stop and the valve shall close.
The location of the thermostat is dependent upon the design engineers specifications. Typically it is located on the wall next to the door of the mechanical room especially if the door has access to the outdoors.
The valve is usually located on the piping near the unit heater and is controlled by thermostat and monitored by the building automation system. Sometimes the unit heater is controlled and monitored by the building automation system so any alarms from the unit heater by the BAS especially in freezing conditions should not be ignored.
Motor Disconnect and Starter Motor is used for turning the power off and on the an electric motor used in HVAC applications. It also has overloads built into the starter so if one of the motor windings begin to pull too many amps the overloads open the circuit and the motor stops operating.
Motor starters are commonly used for 3-phase motors and are used to kill power to the circuit if there is an overload or short circuit. There are solid state motor starters unlike the one pictured that use electronics to detect an overload and other possible motor problems. The one pictured above controls the starting and stopping of the motor via a relay which is located in the bottom right corner of the photo. The relay has a red light on it indicating the motor is on and running. The relay is controlled by direct digital control which offers precision computer control of building systems including HVAC.
A chiller evaporator barrel exchanges heat between one refrigerant and another. Usually the primary refrigerant is R-22, R-134A, or some other blend or alternative HFC. The secondary refrigerant is water. This water is circulated throughout the building where it passes through piping and coils. This is generally in most cases a forced air coil where the heat is removed from the air by a heat exchange process with the water and the coil. The cooler air is then forced through duct work and into the space to be conditioned.
Small Residential Chiller
The water is then pumped back through the chiller barrel evaporator so that the heat absorbed can be removed in the chiller barrel evaporator where another heat exchange process is done. The heat in the water is absorbed into the refrigerant and the water makes another trip to the building to absorb more heat. The refrigerant is then pumped to the compressor where it is compressed and then it travels through a condenser coil or a condenser barrel where the heat it absorbed from the water is rejected. This is the basic process for a chiller. There are many different types of chillers which use different refrigerants but that is the basics of a chillers operation. Chillers range from small residential units to very large multi-tonnage systems which serve very large buildings and process refrigeration in industry.
Smaller chillers are typically air cooled while larger systems use a cooling tower. If the heat in the condenser is rejected vie air then the chiller will have several fans that will pull air through the condenser coils and the heat is rejected into the atmosphere allowing the refrigerant in the condenser coils to cool and then return to the metering device and the evaporator barrel. If the chiller uses a condenser barrel then the heat is rejected into water that is circulated through the same condenser chiller barrel where the refrigerant. Heat is exchanged from the refrigerant to the water. The water is then pumped to a cooling tower where the cooling tower rejects the heat from the water into the atmosphere using the heat exchange process of evaporation.
Commissioning (Cx) any type of HVAC equipment is many different procedures from the beginning of the commissioning process to the end of the process. One of the most important procedures during the Cx process is functional testing. The functional testing always precedes the final testing where a test of all the combined equipment is done in an integrated systems testing. Once successful testing is completed and all discrepancies corrected a final commissioning report is generated including all the test data and information collected during the entire process of testing and commissioning.
Building Automation Program Display
Functional testing of a hot water boiler in the commissioning process can be streamlined if coordinated properly. Much of the Functional Testing Procedure can be accomplished by coordinating with the start up technician or engineer and the test and balance crew. During start up the boiler start up technician should test and verify the proper function of the boiler per manufacturers specifications. During and after the start up the technician should generate a report of all start up work done including adjustments, calibrations, and test data collected during the start up. The Cx Technician or Engineer can then verify first hand essential data needed to complete the Functional Testing Procedure document. The same applies by coordinating with the Test and Balance crew.
After the start up and test and balance is complete and all final reports are received from the start up and test and balance crews then the Cx tech can perform a thorough functional test of the boiler or boiler system. The following are not all inclusive to every boiler installation. The list should be tailored for each individual installation. Initial checks of the boiler should include:
Outside equipment should be checked for proper insulation
Equipment is clean and free of any physical damage including any debris inside of any control panels.
All unit identification tags, piping labels, operating manuals, maintenance checklist, and basic documentation are with the boiler(s).
All pipes have been flushed and strainers cleaned.
All electrical connections are tight including all ground connections.
All breakers for the boiler system including associated pumps are labeled properly for the source.
Boiler drain is accessible and can be drained to a sanitary drain near the boiler drain.
If the boilers are controlled by a building automation system (BAS) ensure the BAS system is checked while performing the procedure. All program functions including alarms, program lock outs, and other BAS variables are checked and ready for testing. Temperature sensors need to be verified for proper installation and location according to representative graphics on the display monitor. All set points and rest schedules need to be verified including the outside air temperature device calibration. Lock outs and reset schedules in the BAS and otherwise needs to be taken into consideration before functional testing. Once all the basics are checked the next step is physical testing as follows:
Start all pumps individually. Check for any noises and for unusual vibrations originating with the pumps individually running and all running at one time. If the pumps are controlled by any speed drives ramp pump up to maximum operating and back down to minimum speed and check for vibrations and unusual noises.
Check all valve actuation for supply, return and any bypass valves.
Test all automatic dampers for combustion air, ventilation and exhaust dampers for proper operation before starting boiler.
Reset all pumps and valves for normal automatic operation and fire the boiler. For dual fuel systems test both different fuel types. Again check for any unusual vibrations and noises. If boiler is a modulating boiler run boiler as minimum, maximum and various stages and verify no unusual noises or vibrations.
On shut down after basic testing ensure proper shut down sequence of the boiler.
Start boiler and shut off pump. Ensure boiler shuts down based on loss of flow. This should be indicated as an alarm with the BAS. After successful testing is complete restore all settings to normal.
Test the high limit setting on the boiler by lowering the temperature setting on the high limit control. Check that boiler shuts down and that the BAS system indicates an alarm.
Test the low water cut-off by disconnecting the wire to the low water cut-off. Ensure the boiler shuts down and all alarms are indicated at the BAS.
Test any safety controls including safety switches such as temperature limit switches.
Check back flow preventer. Ensure no water is leaking from the device.
Test the boiler pressure relief valve by lifting the test gate. Ensure water drains from pressure relief valve.
The test is not all inclusive as the functional test script must be generated and tailored using the mechanical drawings, equipment schedules, project and equipment specifications along with the owner requirements.
If you are in need of commissioning services or written scripts contact High Performance HVAC using our contact page.
There are some facilities including campus like complexes that use a centralized steam plant for various reasons. The steam is generated from a large steam boiler and piped to various buildings around the campus or whatever facility is used. Typically several buildings utilized the steam for heating and hot water for domestic uses including showers, washing dishes, washing clothes and other domestic uses. The steam is usually high pressure and for this reason it is safer to deliver the steam to a mechanical room, reduce the pressure, and run the steam through a steam to hot water generator. A steam to hot water generator is nothing more than a big heat exchanger where at one end steam is delivered and at the other end water is delivered. As the steam runs through the exchanger it exchanges heat with the water heating the water. Thus, producing hot water for domestic use and heating use in the winter.
It is important that the process is controlled so that the hot water generated does not get too hot. The hot water produced can be used in hot water coils and pumped into storage tanks for use later for domestic purposes. Again, it is important to control the temperature as closely as possible to prevent the water from becoming too hot especially for domestic uses where scalding water can be inadvertently delivered to showers and sinks where people can be burned. The steam pumped into the generator is usually superheated and can produced water with very high temperatures.
Variable Air Volume boxes are typically installed in commercial buildings and provide heating and cooling for occupants. There are different types of VAV boxes but how a VAV box works is fundamentally the same from one VAV box type to another.
In many cases a VAV box is nothing but a sheet metal box with a damper and controls inside a control panel. A thermostat connects to the controller while the controller positions the damper based on programmed inputs and variables that include air flow and temperature. Some VAV boxes also have a heat source inside the box. The heat source in many VAV boxes is typically electric but can also be a hot water coil. The thermostat and the controller will also turn on the heat whenever the temperature in the space falls below the set point as determined by the thermostat and pre-programmed temperature limitations in the programming. Usually the building engineer or maintenance staff controls the temperature limitations in the program. This prevents occupants from running the thermostat above certain settings that are unreasonable and possibly overload the HVAC system. These limited set points are usually within reasonable ranges for most peoples’ comfort factor.
Flow Ring inside a VAV Box
The air that is supplied to a VAV box comes from a large air handler and central duct work. The air handler must have the ability to supply the VAV boxes with a variable amount of air as the dampers in the VAV boxes will modulate to different positions based on set point requirements. When the box is in cooling mode the damper will modulate to a nearly fully open position as air conditioning or cooling requires more air flow. Heating requires less air flow so the damper will modulate to a minimum position.
The air handler fan needs to modulate to vary the air flow depending on demand. Typical VAV boxes have a flow sensor inside them to measure air flow. The air flow and temperature variables control damper position based on temperature demands and C.F.M. demands. Another air pressure sensor inside the main duct that supplies air to the boxes measures the pressure inside the duct. There is a pressure set point inside the program of the air handler control. The air handler will ramp up and ramp down the air handler blower to maintain the duct set point requirement in the program.
Variable air volume boxes provide comfort for many people working in commercial buildings. The system is different than the air conditioning and heating systems in our homes but these systems work well and provide good comfort.
The variable air volume box or VAV box is a commercial solution to adding multiple zones to large buildings. VAV boxes offer zoning solutions so that separate zoning demands or temperature selections can be maintained in different areas of the building. If the president of the company wants the temperature in their office to be 70 degrees Fahrenheit but the vice president wants their office to be 74 degrees Fahrenheit then it is possible with the VAV zoning system as long as their VAV boxes are on different zones. This particular VAV box in the picture is not fan powered. It relies on the main VAV air handling unit to provide all the air. Generally, when a fan powered VAV box is calling for heat the damper inside the VAV box closes down so that minimal CFM’s are coming through the primary duct from the air handler. The fan turns on an pulls air from the plenum space above the ceiling. This plenum air is normally warmer than the air inside the occupied space. The heating system kicks in and adds heat to the air until a setpoint is attained. The heat for a VAV box can typically be a hot water coil or electric heat strips. The VAV box in the picture has hot water reheat. Continue reading “Variable Air Volume Box VAV Box Hot Water Reheat” »
Glycol is like antifreeze and is used in chilled water piping loops to prevent freezing. Everyone knows when the pipes freeze they also break and start leaking. Having antifreeze in a chilled water loop is important to prevent freezing. So, how do you keep antifreeze in a condenser water loop when the water/glycol mix goes out to the cooling tower and there is a loss of water/glycol through windage or drift? Meet the glycol make-up unit where it can automatically be added to the water loop and prevent freezing. Antifreeze make-up units range from automatic units that will inject the antifreeze right into the loop to manual units that require an operator to control the process of adding antifreeze to the water loop. These make-up units make it easy to add it to the loop without having a shut-down of the chilled water loop it serves so the loop can continue to run while the glycol is injected directly into the loop. HVAC chilled water loops designed to work at low ambient temperatures need the water/glycol mix to prevent freezing especially for critical facilities like data centers that need to remain operation no matter what the outside temperature conditions are. Percent of antifreeze to water depends on the expected operational temperatures outside so the mix is important for expected operating temperatures. An example of this is listed in the following table (follow equipment manufactures instructions for the recommended mix of antifreeze to water for temperatures):. Each loop requires a different quantity of antifreeze to water mix based on ambient conditions, flow rates and other factors for determining the proper water to glycol mix ratios. Propylene Glycol% to Water
These chilled water actuators control the chilled water for a chilled water system in a data center. There are various sequence of operations for chilled water systems and the sequence of operation is usually always different from one chiller plant to another chiller plant. It depends on the components in the chilled water loop, the application the chilled water system is supplying chilled water for, and what the demand of the system requires for the chiller plant. Some chilled water valves control two-way valves while others control three-way valves. A three-way valve can either be a mixing valve or a diverting valve but the actuators controls the flow in either type of application. Other actuators modulate a valve based on demand. The actuator usually receives its command for position for control from the DDC system or another type of control system. In this case these actuators are controlled by DDC. In the sequence of operation the chiller plant will have a valve line-up usually in a valve matrix that was compiled by the original design engineer and this valve matrix shows the default position of the valves which are controlled by the actuators. Some applications in chilled water piping that are controlled by the actuators include:
The dampers straight across are outside air dampers or make-up air coming from an energy recovery unit. According to the mechanical code commercial buildings require a certain amount of fresh air from the outside to maintain good indoor air quality for the occupants. An energy recovery unit allows the air to be conditioned before being introduced into the building. Other methods include using enthalpy calculations to open economizer dampers and/or CO2 control of the dampers. The dampers at the bottom of the photo are the return air dampers. The return air will mix with the fresh air or outside air and go through the filters where the air is further conditioned based on what the control is calling for based on conditions inside the building, inside the duct work, and outside ambient air temperature. In HVAC using outside air can also be used for free cooling. Continue reading “Outside Air Dampers with Energy Recovery” »