Sub-station

surge protection device boilers and hvac building automation systems

by:KEBO      2019-08-10
The latest state-of-the-Buildings can now be fully automated and remotely controlled, including art sensors, direct digital controls, and computer-driven expert systems.This paper will review what these systems and their operators can and cannot do, what new risks can be generated by boilers in these buildings, and how they can be reduced and controlled.Today, the benefits of automated smart buildings are the use of building automation systems (BAS) and other systems to operate HVAC, boilers, chillers, lamps, fire fighting and other systems in elevator building passages, to achieve the double goal of efficiency and comfort.BAS is defined here as a system for sensors, pilot devices, logic components, controllers, peripheral computers and monitoring devices that provide energy data for central computersEffective control of the interior environment of the building while providing maximum tenant comfort and equipment reliability.BAS offers energy saving, comfort and maintenance/reliability benefits.However, these benefits cannot be achieved unless these systems are properly integrated.System designers must anticipate and overcome the risks outlined below.When the boiler control device is not integrated with BAS at that time, thermal shock can occur in many ways.The most common is the low return water temperature.In a recent claim, a cast iron hot water boiler cracked due to the return of cold water from the system.This building is a single one.Story school, some buildings are far away from the boiler room.In the fall, BAS is programmed to lower the temperature setting values over the weekend.The water in the area serving remote areas has cooled, and when BAS tries to restore the building to a normal occupancy temperature, a cold water breaks the hot boiler section.By installing the timer on the area valve to prevent the problem from being solved at the same time.Control measures have also been added to keep the minimum floor through the longest loop during the temperature reduction operation to keep the minimum temperature.In another case, a chain store reported that when BAS alternate between heating and cooling, the boiler and air conditioning equipment was damaged due to thermal shock.This is getting worse because stores across the country are connected to central BAS.The central BAS computer did not fully take into account the transition from heating to cooling operations and vice versa, resulting in boiler damage and business disruption.Another form of thermal shock can occur in the use of three-Bypass valve.When controlled by outdoor air temperature, these valves allow high bypass, reducing the flow through the boiler.This reduces the temperature delivered to the loop, thus saving energy.When the control is so positive that the way the boiler water is layered is the same as the way the moisture layer in the water heater, there is a problem.In the case that the boiler is required to provide only the minimum input, the burner will cycle frequently.Due to the low overall temperature, the stress ratio of the metal is much higher than the supplier expected or designed.A thermal shock also occurred in the boiler room with external air inlet blinds controlled by BAS.Cold air entering the boiler or equipment room will cool the boiler.If inadequate precautions are provided, a thermal shock, freeze or condensation will occur.Single-The heating and cooling system area of the pipeline is also hit by heat.Single-pipe systems —Pipe system for heating and cooling-Sometimes the initial cost of choosing is low.If heating and cooling are required in a short period of time, there is a good chance that chilled water will enter the boiler.It can cause serious heat shock.Two-pipe systems —Heating and Cooling Using separate pipe circuits-Do not eliminate this risk completely.If the BAS incorrectly sorts the air handling unit and both the heating and cooling coils are in the same unit, the air cooled by the cooling coil will cool the heating coil.This will also cause cold water to return to the boiler.Another more common event occurs when BAS requires 100% external air to save cooling or heating energy.This usually happens in building shared spaces that do not require heating or cooling for comfort.Space such as foyer, lobby, hallway or large meeting room can often receive 100% of outdoor air to solve indoor air quality problems.The heating coil in the air treatment device can withstand low temperature.When the boiler is started or the heating is required in the local area, cold water will impact the boiler.In the space where very strict temperature and humidity control is required, heating-Temperature control-And cooling systemReduced humidity-is needed.Careful attention to the programming of this hot/cold operation is necessary to avoid the possibility of cold water returning to a hot boiler.When the boiler cools to a dew point temperature lower than the combustion product, flue gas condensation occurs during the boiler heating processOn, causing corrosion, breakage and stacking on the surface of the furnace edge.Corrosion is another major cause of boiler accidents.If BAS is programmed to hold the boiler temperature at or slightly above the flue gas dew point, most of the corrosion can be avoided.Boiler start-When the boiler starts with a cold environment, both metals and water are cold.If the boiler is designed to adjust the combustion rate in response to load changes, it is very important to slowly heat the boiler.The metal structure must be allowed to gradually absorb the stress generated as the metal expands with temperature.Most boiler manufacturers include low-fire holding devices in boiler control units to provide boiler preheatingup.BAS programming cannot compromise this protection by moving too early to high ignition.For buildings with multiple or modular boilers, the above hazards are more difficult to deal.In this case, BAS programming must recognize the actual limitations of the operation of boilers in all units.In addition to the mechanical aspects already discussed, there may be other issues with the integrity of the control system.BAS consists of sensors, pilot devices, logic components, controllers, peripheral computers and monitoring devices.All of these devices are sensitive to the following situations.A number of claims have recently been reported concerning electrical and electronic equipment failures caused by electrical transient conditions.Common interruptions come from problems with lighting, internal power fluctuations, harmonics, and power facilities.If there is no proper protection, otherwise the harmless power fluctuation will cause the boiler to be damaged when the BAS fails.Major utility power problems are not common.Lighting arresters, surge protection, and current control make electricity in the United States very reliable.However, one source of local disturbances is not uncommon.Short-term voltage crash-a few cycles —This may occur when utility companies try to adjust the power factor by compensating the inductive load with large capacitor banks.When the capacitor is assembled, the current influx causes the voltage to drop, which may cause local disturbances in the power system.Boiler/BAS solutions consider these suggestions to solve common boiler problems related to BAS: thermal shock through installation 3-As a way to limit the inlet temperature of the boiler, the mixing valve.
Consider using a small mixing pump to prevent temperature stratification in the boiler.
Control low fire hold to heat the boiler according to the boiler manufacturer's guidelines.
Avoid high firesClose when the area is satisfied to avoid rapid temperature changes.
Do not ignore the air side as a potential source of thermal shock.Condensation avoids the control logic of increasing the cycle frequency of the boiler.
Avoid contact with damp external air on the cool boiler surface, or keep the boiler warm.
Keep the minimum temperature of the boiler at or above the dew point of the flue gas.Not only BAS, but all other equipment should be properly grounded.Follow the manufacturer's instructions.
Use an isolation transformer or equivalent device to isolate the AC power connection to the electronic device.
Keep the minimum temperature of the boiler at or above the dew point of the flue gas.Recommended this article covers areas of concern when integrating heating and cooling equipment with automatic building control.The BAS control procedure must recognize the operational limitations of all controlled equipment, as well as conventional energy optimization, HVAC comfort and building safety objectives.Building designers and owners and maintenance and engineering managers should always follow the recommended practices of equipment manufacturers.BAS is able to control and monitor devices and alarms from remote locations.Many states have laws requiring boiler operators to be on site in some cases.BAS's ability to alert based on preset conditions, as well as actions implemented from remote locations, should not replace actions taken by qualified operators on site.
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