busbar trunking system and Cables Difference

Planning concept for power supply:

When a planning concept for power supply is developed, it is not only imperative to observe standards and regulations, it is also important to discuss and clarify economic and technical interrelations (cables and/or busbar trunking systems depending on situations).

The rating and selection of electric equipment, such as distribution boards and transformers, must be performed in such a way that an optimum result for the power system as a whole is kept in mind rather than focusing on individual components.

The most important is that all components must be sufficiently rated to withstand normal operating conditions as well as fault conditions.

Further important aspects to be considered for the creation of an energy concept are //

• Type, use and shape of the building (e.g. high-rise/low-rise building, multi-storey building)
• Load centers and possible power transmission routes and locations for transformers and main distribution boards
• Building-related connection values according to specific area loads that correspond to the building’s type of use
• Statutory provisions and conditions imposed by building authorities
• Requirements of the power distribution network operator
• The following requirements are the main points of interest //
  • Easy and transparent planning
  • Long service life
  • High availability
  • Low fire load
  • Flexible adaptation to changes in the building

  Most applications suggest the use of suitable busbar trunking systems to meet these requirements.

  For this reason, engineering companies increasingly prefer busbar trunking to cable installation for power transmission and distribution. The most common busbar trunking systems ratings are from 25 A to 6,300 A.

Planning Notes

Considering the complexity of modern building projects, transparency and flexibility of power distribution are indispensable requirements. In industry, the focus is on continuous supply of energy as an essential prerequisite for multi-shift production.

The five main advantages of busbar trunking systems are //

1. Straightforward network configuration
2. Low space requirements
3. Easy retrofitting in case of changes of locations and consumer loads
4. High short-circuit strength and low fire load
5. Increased planning security

Power transmission

Power from the transformer to the low voltage switchgear is transmitted by suitable components in the busbar trunking system. These components are installed between transformer and main distribution board, then branching to sub-distribution systems.

Trunking units without tap-off points are used for power transmission. These are available in standard lengths. Besides the standard lengths, the customer can also choose a specific length from various length ranges to suit individual constructive requirements.

Power distribution

Power distribution is the main area of application for busbar trunking systems. This means that electricity cannot just be tapped from a permanently fixed point as with a cable installation. Tapping points can be varied and changed as desired within the entire power distribution system.

In order to tap electricity, you just have plug a tap-off unit on the busbar at the tap-off point. This way a variable distribution system is created for linear and / or area-wide, distributed power supply.

Tap-off points are provided on either or just one side on the straight trunking units. For each busbar trunking system, a wide range of tap-off units is available for the connection of equipment and electricity supply.

Comparison of Busbar and Cables: Temp response derating

Table 1 – Cable / Busbar comparison

Characteristic	Cables	Busbar
Planning, calculation	High determination and calculation expense, the consumer locations must be fixed	Flexible consumer locations, only the total load is required for the planning
Expansions, changes	High expense, interruptions to operation, calculation, risk of damage to the insulation	Low expense as the tap-off units are hot pluggable
Space requirements	More space required because of bending radiuses and the spacing required between parallel cables	Compact directional changes and fittings
Temperature responses and derating	Limits depend on the laying method and cable accumulation. The derating factor must be determined / calculated	Design verified switchgear assembly, limits from manufacturer’s catalogue
Free from halogen	PVC cables are not free from halogen. Halogen-free cables are very expensive	Principally free from halogen
Fire load	Fire load with PVC cable is up to 10 times greater, with PE cable up to 30 times greater than with busbars	Very low, see manufacturer’s catalogue
Design verified switchgear assembly	The operational safety depends on the version	Tested system, non-interchangeable assembly

Chilled Water Pressurization Unit and Chilled Water Vacuum Deaerator

Chilled Water Pressurization Unit

The unit shall consist of:

1   Package assembly of pressurization pump, buffer tank(s) complete with control panel.

Chilled water pressurization unit shall have its control panel connected to the Building Management System to indicate its operational status and whether it is in fault thru a volt free contact (VFC) from the control panel to DDC.

A graphical representation of the plant will be produced with all set points, alarms and time schedules displayed with simple mouse clicks. Access to the graphic will be through a system of site plans, plant rooms and systems.

All values are to be historically recorded at controller level so that locally any laptop or Portable operator’s terminal may retrieve the data as well as the network BMS Supervisor.

Chilled Water Vacuum Deaerator

The unit shall consist of:

Package assembly of pump, vacuum vessel, sensor and valves complete with control panel.

Chilled water vacuum deaerator unit shall have its control panel connected to the Building Management System to indicate its operational status and whether it is in fault through volt free contact (VFC) from vacuum deaerator control panel to DDC.

A graphical representation of the plant will be produced with all set points, alarms and time schedules displayed with simple mouse clicks. Access to the graphic will be through a system of site plans, plant rooms and systems.

All values are to be historically recorded at controller level so that locally any laptop or Portable operator’s terminal may retrieve the data as well as the network BMS Supervisor.

Chilled Water Chemical Treatment System

Chilled Water Chemical Treatment System

The unit shall consist of:

1 Package assembly of chemical dosing system for corrosion, micro biocide and scale inhibitor complete with control panel.

Chilled water chemical treatment system shall have its control panel connected to the Building Management System to indicate its operational status and whether it is in fault thru volt free contact (VFC) from Chemical Treatment system control panel to DDC.

The chilled water chemical treatment system main control panel shall have the facility to provide the following signals to the BMS.

Pump status – run/standby/tripped for each pump

Dosing tank Chemical low level alarm

Common fault

A graphical representation of the plant will be produced with all set points, alarms and time schedules displayed with simple mouse clicks. Access to the graphic will be through a system of site plans, plantrooms and systems.

All values are to be historically recorded at controller level so that locally any laptop or Portable operator’s terminal may retrieve the data as well as the network BMS Supervisor.

Primary and Secondary Chilled Water Pumps and their operation

Primary/Secondary Chilled Water Pumps

The secondary chilled water pump (SCHWP) sets will be controlled through VFD drives to maintain the desired system differential pressure. A minimum of 3 differential pressure transducers will be connected to the DDC controllers of the chilled water system and these shall be used for pump speed control. The differential pressure transducers shall be placed at approximately 2/3 distance on all main sub-branches and on the index run of the Chilled Water network.

The chilled water pump arrangement shall operate as 2 No duty, 1 No standby. Each pump shall be of variable volume type driven via a variable frequency drive, controlled via differential pressure measurement (the sensors shall be located approximately 2/3 of the index circuit) and the operation and controls shall be by the BMS. All cooling equipment shall be provided with 2-port pressure independent control valves for the control of chilled water flow.

When the pumps are signaled to start, the lead pump shall start first and a frequency inverter shall vary the speed of this duty pump depending on the differential pressure in the pipe work network. Differential Pressure in the supply and return chilled water pipe work shall be installed in the index run of each circuit approximately two thirds of the hydraulic distance from the pumps. The exact location of the pressure sensors shall be finalised in accordance with the recommendation of the controls manufacturer. When the chilled water 2-port valves on each AHU/FCU start to open due to increasing load, the differential pressure detector shall send a signal to the BMS, which in turn shall control the VFD on the CHW pumps to maintain the set differential pressure in the pipe work, thus increasing the CHW flow in the circuit.

In the event the lead pump reaches 90% of its maximum speed, its speed increase shall be arrested and the 2nd pump shall start and its speed shall increase until the differential pressure set point is met. Once met the lead pump’s speed shall reduce and the lag pump’s speed shall increase until both pumps have the same speed and are maintaining the differential pressure. From then on the speed of both pumps shall be the same.

When the chilled water demand has reduced to the extent that the duty pumps are operating at less than 40% (say) of their capacity, one of the duty pumps shall be switched off automatically and the other pump shall increase in speed to maintain the set pressure.

The above description is for two chilled water pumps operating in sequence. For three pumps, the sequence is similar except the changeover duty should be matched accordingly.

There shall be water flow proving differential pressure switch across each of the pumps. In the event there is no water flow detected across the pump or an inverter alarm after a pre­determined time delay after the pump has started, or during the operation of the pump, the BMS shall changeover to the stand-by pump and annunciate an alarm.

The BMS shall also monitor the MCC Trip Alarm, Auto Status, VFD Command, Feedback and Pump run status via DPS.

The actual duties at which lead/lag pumps are energised or de-energised shall be determined during the commissioning stage by the controls specialist.

The position of the HOA switches shall be monitored by the BMS and an alarm shall be annunciated on the BMS if any of the switches are not in the normal operating position. Chilled water pump ‘Run’ and ‘Trip’ indication lights shall be provided on the MCC for each pump. Hours run meters shall be provided for all chilled water pumps at the respective MCC.

A graphical representation of the plant will be produced with all set points, alarms and time schedules displayed with simple mouse clicks. Access to the graphic will be through a system of site plans, plantrooms and systems.

All values are to be historically recorded at controller level so that locally any laptop or Portable operator’s terminal may retrieve the data as well as the network BMS Supervisor.

Multiple Zone Variable Volume Type Recirculating Air Handling Units AHU

Multiple Zone Variable Volume Type Recirculating Air Handling Units AHU

The system shall be variable volume package Fresh Air Handling Unit.
The unit shall consist of:

Supply Side

1 Intake motorized damper

2 Panel (Pleated) Filter

3 Bag Filter

4 Cooling Coil

5 Supply Fan (with VFD)

6 Intake and discharge attenuators

7 Sensors and controls (refer to BMS Schematic Diagram)

Exhaust Side

1 Exhaust motorized damper

2 Panel (Pleated Filter)

3 Exhaust fan (with VFD)

4 Intake and Discharge attenuators

5 Sensors and controls (refer to BMS Schematic Diagram)

The Variable Volume AHUs shall operate under the dictates of one of the DDC controllers inbuilt time schedules (adjustable) to suit the operational requirement of the school and control in the following manner.

A hand/off/auto selector switch shall be located on the supply fan control panel. The supply fan motor shall be interlocked to this selector switch, the extract fan fail and the outside air damper proving end switch.

On a command to start the supply fan (thru a VFC from DDC to control Panel) will be enabled and positive indication of this given by means of a differential pressure switch fitted across motor.

The fan shall be enabled when the BMS signals for the air handling plant to operate and the outside air and exhaust air air dampers (modulating) are proven open. The fan operation shall be proven when the differential air pressure switch signal is detected.

When the proven signal is not detected, following a 30 second start up period, a fan failure warning signal shall be sent to the BMS and the fan operation signal shall be removed. The fan operation signal shall be disabled when an overload relay in MCC has tripped.

The supply fan control signal shall be modulated under PI control to obtain the minimum static pressure set points defined during commissioning. The index run VAV box shall be satisfied to have an inlet pressure of 150 Pa (adjustable). The controller shall modulate the supply fan speed utilizing the measured sensor value versus its set point.

The supply fan shall be disabled and a warning sent to the BMS if the supply air pressure rises above a limit of 1500 Pa (adjustable).

Once air flow is established the system will allow its temperature control algorithm to operate. The system will maintain the minimum fresh air requirement (pre-set to ensure that negative pressure is not the encountered) and the fresh air and recirculating dampers will be modulated according to the average space air quality (measured by duct mount C02 sensors to maintain 500 ppm (adjustable) and an alarm shall be generated if the CO2 level remains at 750 ppm continously for a period of 5 minutes) to reduce the load on the plant. This will ensure that high volumes of outdoor air are not unnecessarily cooled.

The actual fresh air volume delivered to the space will be measured by a multi-point velocity detector in the intake ductwork.

The chilled water coil shall be provided with a 2-port pressure independent control valve for supply air dehumidification and sensible cooling. The CHW valve shall be positioned closed when the air handling plant is not operating.

No action is taken when the BMS signals a low outside temperature when the air plant is operational should this ever occur.

The valve shall be positioned to close when a fan failure signal is present. The valve shall fully open when the supply fan is proven and the BMS signals an optimum cooling start operation.

The CHW valve’s position shall be modulated in response to a PI control signal in order to obtain the required set point (design set point of supply air is 12°C) the greatest demand of dehumidification or sensible cooling control shall have priority. The position of the mixing dampers shall be controlled to supply the air to meet indoor CO2 levels.

If the supply air temperature rises above a set point of 25°C and 26°C during summer and winter respectively or below a set point of 12°C during normal operation the BMS shall give a supply air temperature high/low warning.

These AHU’s are distributing conditioned air via VAV units to the conditioned spaces. When the VAV modulating dampers start closing, the pressure in the supply duct rises. The supply air duct is provided with pressure sensor at 2/3rd distance, which gives 0-10vdc signal to DDC corresponding to increase in the duct pressure. On receiving the signal, the DDC gives a 0-10vdc to the fan motor VFD to reduce the speed. The supply pressure set point will be adjustable as per load requirement. The operator can adjust the supply pressure set point from BMS Workstation at any time.

A variable volume return fan shall be provided. The extract fan shall be disabled when the BMS signals a shutdown period.

The exhaust fan operation signal shall be disabled if a supply fan fail signal is received by the BMS. The fan shall be enabled when the BMS signals for the air handling plant to operate and the outside air and exhaust air dampers are proven open. The fan operation shall be proven when the differential air pressure switch signal is detected.

When the proven signal is not detected, following a 30 second start up period, a fan failure warning signal shall be sent to the BMS and the fan operation signal shall be removed. The fan operation signal shall be disabled when an overload relay in MCC has tripped.

The return fan control signal shall be modulated to produce a return air volume flow rate at a ratio of 90% (adjustable) of the supply fan speed or as per static pressure build up due to modulating VAV boxes in the system.

A hand/off/auto selector switch shall be located on the extract fan control panel. The extract fan motor shall be interlocked  to this selector switch, the supply fan fail and the damper proving end switches.

A smoke detection device shall be provided in the return air ductwork. On sensing smoke the supply fan (and extract fan) shall be stopped and an alarm raised at the BMS central supervisor and at the fire alarm main panel. The detector shall be manually reset from Fire Alarm System.

A fire alarm interlock (thru VFC to DDC) shall be hard wired into the control circuit of the AHU to ensure that it shuts down in an alarm condition.

Constant Air volume Air Conditioning System

Constant Air volume Air Conditioning System  Air Handling Units AHU’s

The unit shall consist of:

Supply Side

1. Intake motorized damper.
2. Panel (Pleated) Filter.
3. Bag Filter.
4. Cooling Coil.
5. Supply Fan (with VFD).
6. Plate Heat Exchanger.
7. Intake and discharge attenuators.
8. Wrap Around heat Pipe.
9. Sensors and controls (refer to BMS Schematic Diagram)

Exhaust Side

1. Exhaust motorized damper.
2. Panel (Pleated Filter).
3. Exhaust fan (with VFD).
4. Intake and Discharge attenuators.
5. Sensors and controls (refer to BMS Schematic Diagram)

The constant volume full fresh air type AHU shall start/stop controlled operate under the dictates of one of the DDC controllers inbuilt time schedules initially set to 24 hours operation (adjustable) and control in the following manner.

On a command to start the supply fan will be enabled and positive indication of this given by means of a differential pressure switch fitted across motor.

The fan shall be enabled when the BMS signals for the air handling plant to operate and the outside air and exhaust air air dampers (modulating) are proven open. The fan operation shall be proven when the differential air pressure switch signal is detected.

When the proven signal is not detected, following a 30 second start up period, a fan failure warning signal shall be sent to the BMS and the fan operation signal shall be removed. The fan operation signal shall be disabled when an overload relay in MCC has tripped.

The supply fan control signal shall be fixed control to obtain the required system flow rate defined during commissioning. The controller shall operate utilising a preset time clock (adjustable) to set back the unit flow rate during non-operational hours.

Fan speed will be varied by the use of inverter/VFD drives via hardwire contacts. Fan speed modulation is only to be utilised for commissioning purposes and at the change over from operational and non-operational time periods as defined by the time schedule.

Indication of fan running is provided by means of a differential air pressure switch fitted across the fan which will alarm in the event of failure. Individual indication of “fan trip” and “switch not in auto position” will be provided through the DDC controller.

A hand/off/auto selector switch shall be located on the extract fan control panel. The extract fan motor shall be interlocked to this selector switch, the supply fan fail and the damper proving end switches. The Exhaust will run at the same speed of supply fan.

The supply air temperature set point to swimming pool shall be scheduled to 18°C (adjustable) to maintain room temperature of 28°C.

If the supply air temperature rises above a set point of 18°C or below a set point of 12°C during normal operation the BMS shall give a supply air temperature high/low warning.

The supply air temperature set point is determined according to the strategy selected above.

The space conditions will be maintained by the DDC controller modulating in sequence the cooling valve based on PI control to the satisfaction of the supply air temperature sensors. Positive feedback of valve and damper position will be displayed on the BMS. During commissioning the contractor is to ensure that the PI loop time constants are set to ensure that hunting does not occur due to over cooling of the space.

If the relative humidity reported at the duct mounted supply air humidity sensor rises above its set point of 50-60% (adjustable) and the supply fan is proven by the differential pressure sensors cooling coil and heating coil are to operate in conjunction to dehumidify the supply air by cooling to 12°C (adjustable) with the heating modulating to maintain the space temperatures as defined above.

The above temperature control mode shall be set up and commissioned for the specific project and the set points adjusted and suitable time delays applied to ensure hunting does not occur.

During non-operational periods of the swimming pool as defined by the BMS time clock the AHU volumes are to be adjusted down to the set-back conditions with the control of the cooling coils as defined previously.

Room temperature and relative humidity will be monitored by sensors and displayed at the BMS System. Pre and bag filters in the supply duct will have differential pressure sensors fitted for indication and alarm purposes on the BMS. An alarm shall be generated to BMS in case the differential pressure across each filter bank exceeds the adjustable set-point decided during commissioning.

A graphical representation of the plant will be produced with all set points, alarms and time schedules displayed with simple mouse clicks. Access to the graphic will be through a system of site plans, plant rooms and systems.

All values are to be historically recorded at controller level so that locally any laptop or Portable operator’s terminal may retrieve the data as well as the network BMS Supervisor.

A fire alarm interlock (thru VFC to DDC) shall be hard wired into the control circuit of the AHU to ensure that it shuts down in an alarm condition.

Sump Pumps:

Sump Pumps:

Sump Pump sets will be monitored by the BMS to provide the following information. Each pump will have its Run & Trip status monitored together with the position of its controlling switch. A general fault will be connected to the BMS from the panel together with Hi and Critical Hi Level alarms.

A graphical representation of the plant will be produced with all set points, alarms and time schedules displayed with simple mouse clicks. Access to the graphic will be through a system of site plans, plantrooms and systems.

All values are to be historically recorded at controller level so that locally any laptop or Portable operator’s terminal may retrieve the data as well as the network BMS Supervisor.

Laboratory Waste Sump

Laboratory waste sump shall have on its compartments an actual reading of the water level. Water approaching high level and actual high level alarms will be displayed to control panel (refer to drainage system drawing) and to be connected to BMS thru volt free contact from control panel.

All values are to be historically recorded at controller level so that locally any laptop or Portable operator’s terminal may retrieve the data as well as the network BMS Supervisor.

Pressure Testing of Chilled Water Piping System

Pressure Testing of Chilled Water Piping System:

1. The Chilled water piping shall be tested according to the system working pressure i.e. 1.5 times the working pressure. and/ or PN ratings of the pipes, pipe fittings and valves used in the piping.
2. The piping may be tested in sections or total, depending on site requirements and as per consultant advice.
3. Estimate the piping volume and make arrangement for required quality of clean water.
4. Arrange for temporary piping/ hose pipe connections for filling and draining water.
   
5. Fix the temporary valves at air vent/ drain points and pressure gauges.
6. Fill the piping system with clean water through a temporary pump and obtain the test pressure if no leakage is observed.
7. If leakages are observed, arrange the leakage immediately. If leakages are major, isolate the leaking portion with nearest isolating valve and/ or stop the water filling.
8. Rectify the leakages and again fill with water until no leakages throughout the entire piping system is observed.
9.  After no leakage is observed pressurize the system using hydraulic test pump up to full pressure.
10. During pressurization observe the joints and entire piping system for leakages.
11. Observe the pressure gauges readings for 4 hours and sure that there is no drop in gauge pressure. System pressure to be 1.5 times than the actual working pressure.

Installation of Chilled Water Pipes and Accessories:

Installation of Chilled Water Pipes and Accessories:

The chilled water piping installation method is prepared in order to outline the activities and the methods used for installation of chilled water pipes and accessories. All activities will be carried out in accordance with the contract details and in full compliance to the contract specifications and documents. All work within the rights of way of the standards and specifications will be done in compliance with the requirements issued by authorities.

Tools and Equipment's Required for CHW piping works:

Before starting the chilled water piping installation below mentioned tools shall be arranged and necessary measures will be taken for the safety of the equipment. Relevant entities which might require protect include any such works in the vicinity of the area of work or on the service access or discharge path. The construction team will ensure that any such requirements are documented.

01. Welding Machine.
02. Cutting Equipment's (Oxygen, Acetylene Cylinders and Cutting Torch etc.)
03. Threading Machine.
04. Scaffolding.
05. Lifting Arrangement.
06. Tool Box.
07. Measuring Tape.
08. Spirit Level.
09. Plumb Bob.
10. Steel Hammer.
11. Electric Drilling Machine.
12. Hole Saw Cutter.

Storage Pipes and Accessories:

1. All Piping material while unloading shall not be dropped, but slowly lowered to the ground.
2. Pipes shall be stacked on a flat surface with adequate supports.
3. All pipes to be capped off and extra pipes to be removed for installation area to storage.
4. Any items found damaged or not suitable as per project requirements shall be removed from the site. If require to store temporarily, they shall be clearly marked and stored separately to prevent their use. 

Pre Requirments:

1. Check and ensure all drawings used for installation are latest and approved for construction.
2. Make the pipe routing and support locations as per drawings, and check the co-ordination of piping layout with other services and decide pipe route with minimum bends/offsets.
3. Check and Ensure sufficient Clearance around pipe for applying insulation/cladding as applicable.
4. Clean and apply primer/red oxide on all seamless black steel pipes before installing.

Installation of Chilled Water Pipes:

1. Drill the holes in ceiling/wall for fixing supports, fix the anchors or threaded rods with clevis hangers/structural supports as applicable. Threaded rod length is sufficient to allow for leveling of pipes in future.
2. Cut the pipes accurately to measurements desired at site, and prepare the pipe ends according to the type of joints i.e. Threaded joints or welded joints.
3. Threading shall be done as per fittings/ coupling manufactures recommendations.
4. End preparations for welded joints shall be done as per approved welding procedure.
5. After the end preparation clean the pipe ends and ensure that no material or dust is left inside pipes.
6. Qualified and approved welders with certificates shall be engaged for welding works.
7. Install the pipes sections at heights as per approved drawing in a neat and tidy manner.
8. Insert the rubber inserts between the pipes and supports. 
9. Sleeves of suitable sizes shall be provided as wall crossings/openings.
10. Install the valves in locations as per approved drawings.
11. Install the piping connections with valves and accessories where ever equipment's are installed as per approved drawings and technical specifications.
12. Fix the blind plugs/temporary valves on all drain, air vent, pressure gauge, thermometer, and test points trapping etc as per approved drawings.
13. Check and ensure proper supporting is provided as per approved drawing.
14. While installation is going on of the pipe work, the insulation will be fitted to the pipe work, But all fittings and joints will be left until the pressure testing and inspection is completed and approved.
15. Raise the inspection for chilled water piping installation to consultant. Obtain sign off for hydraulic pressure testing after the test is witnessed.

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Psychrometric Chart?

A Psychrometric Chart is an important tool for HVAC engineers to carry out heat load or cooling load calculationsand find solutions to various air condition related problems. Read an overview of the components included in a psychrometric chart.

• The series of articles on properties of air discussed important properties of air like relative humidity, dry bulb temperature, wet bulb temperature, dew point temperature, sensible heat and latent heat. We shall now see how the air behaves when it is subjected to changes in temperature and humidity to suit the various applications for which the air conditioning is meant. The behavior of the air can be studied very conveniently and accurately by using a psychrometric chart.
• Psychrometric charts are graphic representations of the psychrometric properties of air. By using psychrometric charts HVAC engineers can graphically analyze different types of psychrometric processes and find solution to many practical problems without having to carry out long and tedious mathematical calculations.
  The psychrometric chart looks complicated with vast numbers of lines and curves in it, but is very easy to understand if you know the basic properties of air. You will also understand its worth when you actually use it considering the fact that you won’t have to use any formulae to find the properties of air in different conditions, all you will have to know is two parameters of air and the rest are easily found on the chart.

• Various Lines and Curves in the Psychrometric Chart

  All the properties of air indicated in the psychrometric chart are calculated at the standard atmospheric pressure. For other pressures relevant corrections have to be applied. The psychrometric chart looks like a shoe. The various lines shown in the chart are as follows (please refer the figs below):

• • 1) Dry Bulb (DB) Temperature Lines:

    The dry bulb temperature scale is shown along the base of the shoe shaped psychrometric chart forming the sole. The DB temperature increases from the left to the right. The vertical lines shown in the chart are the constant DB temperature lines and all the points located along a particular vertical line have same DB temperature.

  • 2) Moisture Content:

     is the water vapor present in the air and is measured in gram per kg of dry air (gm/kg of dry air). The moisture present within the air is indicated by the vertical scale located towards the extreme right. The horizontal lines starting from this vertical scale are constant moisture lines.

  • 3) Wet Bulb (WB) Temperature Lines:

    The outermost curve along the left side indicates the Wet Bulb (WB) temperature scale. The constant WB temperature lines are the diagonal lines extending from WB temperature curved scale downwards towards the right hand side of the chart. All the points located along the constant WB temperature line have the same temperature.

  • 4) Dew Point (DP) Temperature Lines:

    Since the dew point temperature of the air depends on the moisture content of the air, constant moisture lines are also constant DP temperature lines. The scale of the DP and WB temperature is the same, however, while the constant WB temperature lines are diagonal lines extending downwards, the constant DP temperature lines are horizontal lines. Thus the constant DP and WB temperature lines are different.

Air and Water Cooled Chillers:

Difference Between Air and Water Cooled Chillers:

In a window air conditioner, refrigerant is flowing through the coil that cools the room's air.

In a chilled water air conditioning system, cold water is flowing through the coil that cools the room's air.

The air conditioning machine that cools the water is called a chiller, and it will be located in a dedicated machinery area somewhere in the building, on the roof, or outside.

In the chiller, refrigerant flows through the coil that cools the chilled water.
The chilled water is pumped through a piping loop to air handlers in the spaces to be cooled, where it absorbs heat from the air that flows over the air handling coil.

The warmed up water then returns through the piping loop back to the chiller, where the heat it absorbed is released to the refrigerant flowing through the chiller's evaporator coil.

The chilled water circuit of a typical water chiller system will consist of a pump, cooling coils, expansion tank, and piping valves and controls, in a closed loop.

The temperature of the chilled water supplied to the loop will depend on the set point of the chiller.

The temperature in the spaces being cooled will be controlled by thermostats.

They will sense room temperature, and keep the room at the set temperature by controlling water flow and/or air flow through the air handler.

The compressor in the chiller unit might be a reciprocating type, a screw type, a scroll type, or it might be a centrifugal compressor.

On a water cooled chiller, water flows through the condenser to cool the hot discharge gas to condensing temperature.

On an air cooled chiller, air flows through the condenser coils to cool the hot discharge gas to condensing temperature.

An air cooled water chiller system with a reciprocating compressor will operate at pressures and temperatures very similar to those of a window air conditioner that's running in the same outdoor climate, with the same indoor room temperature.

The normal temperature for the chilled water leaving the chiller is about 44°or 45°, so the low side pressure should be equivalent to about 35° to 38° when the water is near 44° to 45°, which is only a few degrees below the design evaporating temperature for a window air conditioner.

Superheat will depend on the manufacturer's specifications, but I would expect a water chiller system with a reciprocating compressor to have 20° to 30° of superheat at the compressor inlet.

You'd look for much the same conditions in a window air conditioner.

The design chilled water temperature drop through the chiller is normally 10°, so when the supply chilled water temperature is at or near 44° to 45°, look for the chilled water to be returning to the chiller at about 54° to 55°.

Condensing pressure should be equivalent to 20° to 35° above ambient temperature.
Look for the air temperature to rise 20° to 30° through the condenser coil.
A rise of over 30° is too high.

Similar to what you'd look for in a window air conditioner.

Look for 10° to 15° of subcooling, unless the manufacturer specifies otherwise.

Once again, similar to what you'd find in a window air conditioner.

Are you troubleshooting the solid state controls on a large water chiller system?
If so, you're going to have to get a copy of the manufacturers troubleshooting guide for the controls, or else bring in a professional technician who has the manuals and knows how to use them.

With regard to water chiller system operating pressures and temperatures, you might find our Chiller Evaluation Manual helpful.
It has cycle diagrams for air cooled and water cooled chillers, and guidance about evaluating a chiller's pressure and temperature readings.

With regards to maintenance, a water chiller system requires more maintenance than a standard air conditioning system, and our Chiller Maintenance page will introduce you to some important maintenance procedures.

Special Considerations in HVAC

Special Considerations in HVAC:

Some situations require special attention with respect to the HVAC system. This section lists a few examples from the many situations where HVAC systems play a key role in success or failure.

Some applications have strict requirements for precise temperature and humidity control. These include food processing, storage of perishables, certain industrial
processes, chemical processing and storage, computer rooms, green houses and other applications where a few degrees difference in temperature could mean the ruin
of costly product or equipment.

In some laboratories and health care facilities, the potential for the migration of dangerous or infectious substances is a concern. Patients recovering from surgery, transplants or other immune compromised conditions are especially prone to airborne infections and may require special
consideration with respect to filtration and ventilation. (TSI has published a brochure featuring instrumentation for managing differential pressure in health care facilities. Visit our website www.mepsite.blogspot.in
Cleanrooms in the semiconductor industry require very stringent filtration and control of ambient air. Here, even a small breach in contamination control could mean the loss of a considerable amount of valuable product.

Many buildings have adjacent or underground parking areas and controlling the introduction of vehicle emissions into the building is imperative. Smoking restrictions have been implemented in
public buildings, restaurants and many corporate facilities. In general, proper exhaust and ventilation is an important concern to rid the building of unwanted contaminants.

During construction or renovation, special attention must be paid to the HVAC system to contain and control unwanted airborne contamination and prevent it from migrating to other areas of a building. Maintaining negative relative pressure in the construction area is an important
consideration along with special filtration and, perhaps, dedicated exhaust. Another matter regarding our national interest is protecting buildings from the infiltration of dangerous material, particularly airborne nuclear, biological or chemical (NBC)agents. Here special consideration must be given to controlling and protecting the outdoor air intake, filtration,the level of uncontrolled leakage and the ability of the system to purge a building. Mechanical ventilation systems have various controls to regulate air flow and pressure in a building that can
be essential in an emergency response situation. In some cases, with sufficient time, it may be wise to shut off the building’s HVAC and exhaust system to help prevent the introduction of NBC agents. Other times, the system can be used to regulate pressure and airflow to control the migration or spread of unwanted agents through the building. Special training for building personnel may be required for them to recognize situations requiring certain action and be familiar with the proper plan of action.

Efficiency vs. Effectiveness

Efficiency vs. Effectiveness:

With any mechanical ventilation system, there is a trade-off between optimizing occupant comfort and controlling operating costs. Common measurements for assessing effectiveness or the level of comfort among occupants include a variety of parameters such as temperature, humidity, air velocity, ventilation, vibration and noise. Individual perception plays a significant role since comfort is both physical and psychological and can vary greatly by individual. What is
comfortable for one person may be too warm for the next and too cool for a third.
When maximizing the operating efficiency of a system, a number of factors must be considered including fuel source and cost, electrical consumption, air filtration, equipment life, maintenance costs and more. These expenditures are often very visible. Controlling them has a direct impact on the day-to-day cost of building operation and can impact a company’s profitability. Reducing HVAC operating expenditures to a point where occupants are dissatisfied has other costs associated with it, including increased costs due to absenteeism, loss of people due to employee turnover, recruiting, training and decreased productivity to name but a few. So it is important to balance comfort against cost so both are optimized.

Heating Ventilation and Air Conditioning(HVAC)

Heating, Ventilating, and Air Conditioning (HVAC):

Relates to systems that perform processes designed to regulate the air conditions within buildings for the comfort and safety of occupants or for commercial and industrial processes or for storage of goods. HVAC systems condition and move air to desired areas of an indoor environment to create and maintain desirable temperature, humidity, ventilation and air purity. Depending on geographic location and building construction, various types of interior climate control systems help ensure that interior spaces are maintained at comfortable levels year-round.

With today’s energy conservation concerns, buildings are constructed to be much tighter, reducing the level of natural exchange between indoor and outdoor air. As a result, more and more buildings rely on mechanical conditioning and distribution systems for managing air.

A properly operated HVAC system finds the often-delicate balance between optimizing occupant comfort while controlling operating costs. Comfort is an important issue for occupant satisfaction, which can directly affect concentration and productivity. At the same time, controlling these comfort and health parameters directly affects HVAC system operating costs in terms of energy, maintenance and equipment life.

What is the Balancing Valve function?

Balancing Valves. 

Balancing valves (Circuit Setters) are used to impose artificial head in all pipe routes besides the critical one to prevent short circuiting (excessive flow through lower pressure drop paths that results in insufficient flow through the highest pressure drop path). These valves are usually located on the return side (outlet) of the device as because this subjects their elastomers to lesser extremes of temperature and pressure, extending their lives. The most common type of balancing valve consists of a variable orifice and two pressure taps to measure the pressure differential across the valve. The flow rate is determined by measuring the pressure drop and noting the opening position of the variable orifice. Then a chart is used to find the flow rate.

Another type of balancing valve uses a flow sensor to measure the flow rate, plus some type of throttling valve, impeller trimming, or a variable speed drive to limit the maximum flow rate. This approach is generally more expensive, but has lower pressure drop and reduces pumping energy.

Automatic flow-limiting valves are preferred by some designers. They consist of a spring and variable orifice to limit the flow rate to the maximum intended for that flow path. They are commonly applied on heat pumps.

One apprehension with this type of control device is that there is often no way to measure flow other than to assume that the automatic flow limiting valve is operating properly. There is also no way to adjust the maximum flow rate without replacing the automatic balancing valve. The advantage is that no manual balancing is required if they operate properly and are not fouled by debris in the piping.

There is also a combined balancing valve which includes a shutoff valve.

There are 2 ports which are located on each side of the balancing valve for measuring the input and output flow rate for balancing.

Psychrometry

PSYCHRMETRY:

Moisture, air, and heat interact with some consequences that are threats to, and other consequences
that are opportunities for, building performance. In winter, condensation within insulation due to falling
air temperatures can be disastrous. In summer, adding moisture to hot, dry air can lower its drybulb
(DB) temperature while raising its humidity to more comfortable levels.

These moisture, air, and heat interactions are complex. As air temperature rises, its capacity to hold
moisture rises also, and the warmer air becomes less dense. These combined interactions are described
by psychrometry, the study of moist air. Fortunately, these interactions can be combined within a single
chart. Dry‐bulb (DB), wet‐bulb (WB) and relative humidity (RH) elements are combined in the schematic chart, where the term saturation line, at 100% RH, is introduced. This is also called the dew point (DP) because dew forms (water vapor condenses) when saturated air touches any surface at or below the air’s dew point temperature. This saturation is sometimes undesirable, as within walls or roofs, or on ceiling, air duct, or glass surfaces. However, it is often desirable, as on air‐conditioner coils, where the resulting reduction of the moisture content in the air is deliberate.

The psychrometric chart may be used to graph a wide variety of processes. The first addition
is the humidity ratio, which indicates the amount of moisture by weight within a given weight of dry air.
Air treatment processes that travel along these horizontal lines of constant humidity ratio are
the familiar processes of simple heating (air passing through the heating coil of a furnace or through
a solar collector) and simple (sensible) cooling (air passing through the cooling coil of an air conditioner
before saturation). The humidity ratio is used in calculating latent heat gains from outdoor air.

The next addition shows how the density of air varies as its temperature and moisture content vary.
These lines are those of specific volume, the reciprocal of density, a useful quantity in air‐conditioning
calculations and helpful in understanding the stack effect in passive design. The specific volume is given
in ft3/lb (m3/kg) of dry air.

The next addition  involves enthalpy, the sum of the sensible and latent heat content of an air–moisture mixture relative to the sum of the sensible and latent heat in air at 0°F (0°C in SI units) at standard atmospheric pressure. Enthalpy units are Btu/lb (kJ/kg) of dry air. Enthalpy lines are almost parallel to those of WB temperature. Perhaps the most familiar process to travel along the lines of constant enthalpy is evaporative cooling, whereby increased moisture and lower air DB temperature are obtained without changing the enthalpy (total heat content) of the air. There is indeed a drop in sensible heat as the temperature drops, but this is matched by an increase in latent heat as the moisture content increases. The opposite process is chemical (desiccant) dehumidifying, whereby decreased moisture content is obtained at
the price of increased air DB temperature; again, no change in enthalpy (total heat) occurs.