Optimizing Pumping Schemes In...
Transcript of Optimizing Pumping Schemes In...
By GRUNDFOSRonak Monga Product Manager – HVAC, Greater Middle East (GME)
Optimizing Pumping Schemes In Air‐Conditioning
14th January 2017Doha, Qatar
CHILLED WATER PLANTS
WOULD YOU LIKE TO?
Simplify your chilled water system and save money at the same time?
Ensure that low ΔT will not be a problem?
Leave out components, save initial cost and still keep up good comfort?
Invest less and get lower operation cost?
AGENDA
Ways Of Optimizing Pump Schemes In Air‐Conditioning Constant flow systems Constant primary / variable flow secondary systems Primary / secondary / tertiary pumping systems Variable primary flow systems
Open Loop Systems Designing open loop systems & considerations for condenser
water distribution Optimizing cooling tower design
District Cooling Systems A look into district cooling systems Typical components of district cooling Why choose district cooling
Efficient Chilled Water Plants Chilled water plant energy split Characteristics of an efficient chilled water plant & chilled water system design Role of pumps in air‐conditioning
1
2
3
4
AGENDA
Trends In Air‐Conditioning Pumping
Passive Systems In Air‐Conditioning Radiant cooling systems (Floor cooling & Wall cooling systems)5
6
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ENERGY SPLIT IN A TYPICAL COMMERCIAL BUILDING
Source: Bluehatmechanical
44%
28%
14%
4%
2%1%
7% HVAC
Lighting
Ofc. Equipment
Water Heat
Refrigeration
Cooking
Other
44% of a commercial building’s energy consumption is attributed to HVAC systems
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CHARACTERISTICS OF AN EFFICIENT CHILLER PLANT:
Efficient design concepts
Efficient components
Proper installation, commissioning and operation
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EFFICIENT CHILLER PLANT DESIGN:
Focus on chiller part load efficiency
Design efficient pumping systems
Proper selection of cooling tower
Integrate chiller controls
Commissioning of system
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EFFICIENT CHILLER PLANT DESIGN:
Focus on chiller part load efficiency
Design efficient pumping systems
Proper selection of cooling tower
Integrate chiller controls
Commissioning of system
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LOOK AT AIR‐CONDITIONING AS A SYSTEM, NOT IN ISOLATION..
Performance Of The System Depends On Each Individual ComponentSystem Knowledge Is Vital For Ensuring The Optimal Performance
More Important Than Looking At Individual KW Ratings Is The KW/Ton Rating Of The Plant
Chiller
Cooling Tower Cooling Ceiling/Floors
Cooling Surface
SecondaryPumps
Heat Recovery Fan Coils
Buffer Tank
PrimaryPump
PressureHolding
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ROLE OF PUMPS IN AIR‐CONDITIONING
A Centrifugal pump is the workhorse of any HVAC system, in chillers, boilers, cooling towers, make up water systems and hydronic distribution systems.
Changes in centrifugal pump technology has been evolutionary rather than revolutionary… over the years.
But with the convergence of power electronics and control technology, the way these pumps are controlled have become the differentiating factors among the manufacturers….
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INTRODUCTION TO CHILLED WATER PIPING SCHEMES:
Constant flow system
Constant primary/variable flow secondary systems
Primary/secondary/tertiary pumping systems
Variable primary flow systems
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CONSTANT FLOW SYSTEMS
High Pump Power Consumption
Loss of Cooling Performance
Primary Pumps
Cooling Loads
3way control valves
Chi
ller -
3
Chi
ller -
2
Chi
ller -
1
Constant
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CONSTANT FLOW SYSTEMS
Chilled water is pumped at a constant flow rate which is independent of the cooling load
During part load conditions, which occurs op to 80% of the time, three way control valves at cooling coils are used to bypass the chilled water back to return line
Chilled water mixes with return water from the cooling coils and this results in lower chilled water return temperature to plant
This lower return water temperature reduces the temperature differential (ΔT) across the chillers
This method of chilled water pumping, results in a significant waste of energy and loss of performance of the main chiller plant due to low ΔT syndrome.
Primary Pumps
Cooling Loads
3 Way Control Valves
Chiller ‐3
Chiller ‐2
Chiller ‐1
Constant
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CONSEQUENCE OF ”LOW DT SYNDROME”NORM
ALDT
Flow Temperature: 7 °C Return Temperature: 14 °CDT: 7 °C
= 1.800 kW
Q = F x 0,86 = 1.800 kW x 0,86 = 221 m3/hDT 7 °C
LOW
DT
Flow Temperature: 7 °CReturn Temperature: 12 °CDTreduced: 5 °C
Q = 221 m3/h
Freduced = 221 m3/h x 5 °C = 1.285 kW 0,86
Performance Reduction By
29 %
Constant
Constant
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CONSTANT PRIMARY / VARIABLE FLOW SECONDARY SYSTEMS
Constant Primary Flow
Variable Secondary Flow
More Energy Efficient
Chi
ller -
3
Chi
ller -
2
Chi
ller -
1
De‐cou
pler
SecondaryPumps
PrimaryPumps
2way control valves
DP
Secondary Control Panel
ConstantVariable
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CONSTANT PRIMARY / VARIABLE FLOW SECONDARY SYSTEMS
A primary‐secondary pumping scheme divides the chilled water system into two distinct circuits that are hydraulically separated by a de‐coupler (neutral bridge)
In primary/secondary systems, chilled water flows through the chiller primary loop at a constant flow rate, whereas in secondary loop, flow rate is varied using a control system. The hydraulic independence of each loop prevents variable flow in the secondary loop from influencing the constant flow in the primary loop
This is a well proven traditional scheme which is still in use
Primary pumps are of constant speed and sized for head & flow required in the (production) primary loop alone
Secondary pumps are of variable speed and sized to deliver chilled water through the distribution network to connected loads
When the flow through de‐coupler happens, the direction of the flow gives an indication of plant capacity, to trigger a start/stop of chiller in the plant
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CONSTANT PRIMARY / VARIABLE FLOW SECONDARY SYSTEMS
WHERE TO USE: Chillers cannot handle variable flow :• If the chiller evaporator coil cannot accept /
operate with varying chilled water flow
Loads and flows do not vary:• System has steady process loads or TES
systems. Investment in variable flow systems is not economically viable solution
Familiarity of operations team:• Facility owners, operators and contractors
are far more comfortable with primary‐secondary systems and understand the nuances better than complex systems
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DE‐COUPLER SIZING
The de‐coupler should be sized for the flow rate of the largest primary pump or largest chiller in the plant room. For simplicity of design and installation, the common pipe is often the same diameter as distribution.
The maximum pressure drop in the de‐coupler pipe shall not exceed 4.5 kPa (1.5 ft). Establish the pressure drop in the common pipe by assuming the flow of the largest chiller pump is passing through the common pipe. The resultant pressure drop should not exceed 4.5 kPA (1.5 ft.)
When the pressure drop in the de‐coupler is restricted to 4.5 kPa (1.5 ft), chilled water will not enter into the secondary loop until the pump is switched on. Higher pressure drop in the de‐coupler line makes the primary and secondary loop to be in series.
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DE‐COUPLER SIZING
Distance between the T‐ joints between secondary and primary headers where this de‐coupler line is located must be at least of 3 pipe diameters. Lengthy pipes may result in excessive pressure drop greater than 4.5 kPa resulting in adverse effects as indicated above.
Length of de‐coupler T‐joint from the first chiller should be of minimum 10 pipe diameters to avoid possibility of stratification in the chilled water return line header. Since the temperature transmitters are fixed close to these, proper lengths are to be provided for proper mixing and correct temperature reading to avoid chiller cycling.
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PRIMARY / SECONDARY / TERTIARY FLOW SYSTEMS
Zone Divided
Increased Energy Efficiency
Constant Variable Variable
Tertiary Pump
Chiller ‐3
Chiller ‐2
Chiller ‐1
De‐cou
pler
Tertiary Pump
Building 3Building 4
Room
Primary Pumps
Secondary Pumps
Tertiary Pump
Build
ing 1
Build
ing 2
Chiller Plant Room Tertiary Pump
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PRIMARY / SECONDARY / TERTIARY FLOW SYSTEM
Proportional Pressure Control Based On P
Tertiary pump
ConstantVariableVariable
P
P
Pump Controller
Cooling Loads
Tertiary Pump
Supply 7 oC
Return 13 oC
Signal to secondary pump controller
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PRIMARY / SECONDARY / TERTIARY FLOW SYSTEM
When the buildings are distributed to larger area, these “primary‐secondary‐tertiary” schemes help to reduce the pump pressures in the system. By splitting the system head between the secondary and tertiary pumps, excessive pressurization in zones which do not need high pressure are reduced.
Primary pumps are of constant speed and sized for head & flow required in the (production) primary loop alone
Secondary pumps are of variable speed and sized to deliver chilled water through the distribution network alone
A tertiary system at each of the buildings take care of localized pumping needs. Tertiary pumps are sized for the flow and head for that building pipe net.
A mixing loop controller with 3 temperature sensors control the blending of return chilled water with the supply whenever there is less load at the building, thereby controlling the return chilled water temperature to the main plant. This increases the plant efficiency as the return chilled water temperature is maintained close to the design thereby minimizing the low delta T syndrome.
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PRIMARY / SECONDARY / TERTIARY FLOW SYSTEM
WHERE TO USE: To have localized control within
buildings:• This gives flexibility in sizing the local or
tertiary pumps to suit customer’s needs
Lower distribution pumping energy:• Centralized distribution pumps must
produce the head required to serve the most hydraulically distant customer
To improve plant efficiency in large campus systems:
• By controlling the blending of return chilled water with supply through a mixing loop at tertiary zone, plant efficiency is improved
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VARIABLE PRIMARY FLOW SYSTEMS
Flow meters
Chi
ller -
1
Chi
ller -
2
Chi
ller -
3
Primary Pumps
De-
coup
ler
Minimum flow bypass valve
normally closed
CoolingLoads
2way controlvalves
Variable
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VARIABLE PRIMARY FLOW SYSTEMS With the advent of more sophisticated control
systems and improvement in chiller technology over the past few decades, variable primary flow systems are widely used now, in the air conditioning industry. It has a first cost savings straight away, as it eliminates secondary distribution pumps, associated pipes & accessories from the circuit.
Here the primary pump is sized for circulating chilled water through the chiller evaporator coil and further to the cooling coil loads. These pumps are equipped with variable frequency drives to vary the flow within the system to meet the operating conditions.
There are certain limitations within which VPF systems has to be designed:DESIGN LIMITATIONS
1. Chiller manufacturers recommend a safe minimum flow beyond which flow should not be reduced.
2. Velocity of flow through evaporator to be maintained between 1 to 3 m/s (varies between manufacturers) to contain tube erosion.
3. Rate of change of flow through the chiller should be as described by the respective chiller manufacturer.
4. Chillers in parallel configuration are to be of equal capacity.
5. System should be tolerant on temperature variations.
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VARIABLE PRIMARY FLOW SYSTEMS
FLOW & VELOCITY LIMITATIONS1. Every chiller manufacturer recommends the
minimum flow range which can be pumped through the evaporator coil. Turn down ratio depends on chiller type also. Normally the minimum evaporator coil flow is 40 to 60% of the design flow.
2. Any operation of the chiller less than the safe minimum flow will result in ice formation in the tubes leading to tube burst potentially damaging the whole equipment itself.
3. Low velocity limits of 1 m/s, is to prevent laminar flow and also to keep the evaporator tubes clean.
4. High velocity limit of 3 m/s is to avoid evaporator erosion.
5. System should be tolerant on temperature variations.
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MINIMUM FLOW BYPASS VALVE
12 M3/H
8 M3/H
12 M3/H20 M3/H
Chiller
20 M3/H
Controller
Minimum Flow Bypass Valve
Normally Closed
Cooling Loads
2 Way Control Valves
Variable
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MINIMUM FLOW BYPASS VALVE
In VPF systems, the bypass valve in common line is generally closed to allow the variable speed primary pumps to cater to load requirement directly. But when the cooling load requirement falls to a level where the necessary flow is less than the safe minimum flow that needs to be pumping through the evaporator coils (as per chiller manufacturer’s recommendation), there is excess pumping involved in the chiller plant.
Selecting an appropriate valve actuator is critical to ensure the proper functioning of the bypass function. One which maintains a linear relationship between the valve position and flow rate will do.
Can bypass valves be avoided in VPF systems ? ‐ Yes, if the building load does not fall to a level lower than the chiller safe minimum flow as suggested by chiller manufacturers. I.e., the base load of the building stays well above.
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MINIMUM FLOW BYPASS VALVE
BYPASS VALVE CONTROL
When the cooling loads are reducing, a point comes where the active chiller reaches it safe minimum flow which is much greater than what is needed at the cooling coils.
Closing of 2 way valves at cooling coils makes the differential pressure to increase in the system, but since the pump flow is limited by chiller safe minimum flow, the increase in pressure makes the pump operating point to shift to its left.
If the excess flow is not diverted in the bypass line, due to drop in flow, system might trip owing to low flow condition.
For example, say if the cooling coils need only 12 m3/h whereas the minimum safe recommended evaporator coil flow in the active chiller itself is 20 m3/h, the excess 8 m3/h is diverted through bypass line.
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CONTROL OF VARIABLE PRIMARY FLOW SYSTEM
CHILLER
CHILLER
CHILLER
DP
DP
AH
Us
FLOW METERS
MIN FLOW BYPASS VALVE
SYSTEM FLOW METER
AH
Us
AH
Us
DP
TT
DP
CHILLER PLAN
T MAN
AGER
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VARIABLE PRIMARY FLOW SYSTEMS
In this scheme, flow is allowed to vary through the chiller downwards up to 40% of design.
Variable primary flow systems use 25‐40% less energy than traditional constant primary/variable secondary pumping scheme.
Secondary distribution pumps are totally eliminated and primary pumps are sized for the flow and head to cater up to the building loads through the chiller plant.
A minimum flow bypass control valve is placed in de‐coupler line, which bypasses flow back to plant when the production flow is higher than building demand.
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VARIABLE PRIMARY FLOW SYSTEMS
WHERE TO USE: Systems where cooling load and flow
varies:• System designed for variable flow especially
in hotels & commercial establishments
Where foot print is a premium:• With lesser no of pumps and accessories, it
gives the investor more sellable space
Where temperature variation is acceptable:
• There will be a slight raise in supply temperature whenever chillers are staging in. Process cooling does not permit this raise as humidity control will be lost affecting the product.
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LOCATION OF DIFFERENTIAL PRESSURE SENSOR
Location of differential pressure sensor is critical in the performance of variable volume pumping system be it primary/secondary or variable primary flow system.
Only if the DP sensor is located at the most critical zones, it can sense the load changes effectively to modulate the distribution pumps.
For direct return piping scheme like the one shown below, load closest to the plant having the shortest path will experience entire pump head. Pressure drop is minimal near to the plant and it is substantial at the end of the piping. Here balancing valves are required to ensure right flow to each circuit.
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LOCATION OF DIFFERENTIAL PRESSURE SENSOR
For reverse return piping scheme, pressure drop is theoretically the same across all load points due to equal length of piping from the chiller plant to the cooling loads. Pressure drop is nearly the same from the plant to the end of the piping.
Decision to use direct return or reverse return piping is based on system operability vs fi rst cost, and it is left to the designer and the owner to decide.
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SINGLE DP SENSOR OR MULTIPLE SENSORS?
Always there is a question on whether to use single sensor in the system or need to use multiple sensor to ascertain the load changes.
One DP sensor is good enough for closed loop application as change in load affects complete piping system and if the DP sensor is located correctly then it can sense the load changes.
When a larger number of sensors are used unnec‐ essarily in the smaller piping system, too many sensing points increase the scan time and at any point of time, if one or the other sensor is having a deviation from the set point, the pump controller will try to respond –making the system unstable.
Key is to avoid too many sensors, have either one or maximum two in the system and locate it properly in the piping network.
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WAYS OF OPTIMIZING PUMPING SCHEMES IN AIR‐CONDITIONING
IMPR
OVE
D PE
RFORM
ANCE
IMPR
OVE
D PE
RFORM
ANCE
Chiller
Chiller
Chiller
Load
Load
Load
Load
Load
Load
Load
Load
Load
Constant FlowThree Way ValvesConstant Speed Pumps
Chiller
Chiller
Chiller
Load
Load
Load
Load
Load
Load
Load
Load
Load
Constant FlowThree Way ValvesConstant Speed Pumps
Chiller
Chiller
Chiller
Load
Load
Load
Load
Load
Load
Load
Load
LoadCommonPipe
Constant Flow (Primary)Variable Flow (Secondary)Two Way ValvesConstant/Variable Speed Pumps
Chiller
Chiller
Chiller
Load
Load
Load
Load
Load
Load
Load
Load
LoadCommonPipe
Constant Flow (Primary)Variable Flow (Secondary)Two Way ValvesConstant/Variable Speed Pumps
Chiller
Chiller
Chiller
Load
Load
Load
Load
Load
Load
Load
Load
LoadBuffer Tank
Constant Flow (Primary)Variable Flow (Secondary)Two Way ValvesConstant/Variable Speed Pumps
Chiller
Chiller
Chiller
Load
Load
Load
Load
Load
Load
Load
Load
LoadBuffer Tank
Constant Flow (Primary)Variable Flow (Secondary)Two Way ValvesConstant/Variable Speed Pumps
Chiller
Chiller
Chiller
Load
Load
Load
Load
Load
Load
Load
Load
Load
Variable FlowTwo Way ValvesVariable Speed Pumps
Chiller
Chiller
Chiller
Load
Load
Load
Load
Load
Load
Load
Load
Load
Variable FlowTwo Way ValvesVariable Speed Pumps
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DESIGN CONSIDERATION IN CHILLED WATER DISTRIBUTION
POINTS TO NOTE: Design of chilled water pumping
system is to move the water with the highest efficiency and lowest energy consumption possible.
Chilled water distribution systems should be configured to avoid interference with the efficient operation of chillers.
Complicated pumping systems to save pumping energy at the expense of chiller energy consumption to be avoided.
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OPEN LOOP SYSTEMS
Open systems are systems, where the pump is used to transport liquid from one point to another.
Condenser water pumping system in air conditioning application are considered to be open loop system as the media (water) is open to atmosphere at cooling tower.
Please note that in open loop system static head requirement is different from that of a closed loop chilled water circulation system.
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OPEN LOOP SYSTEMS
That means, when the condenser water pump is stopped, water gets filled in the pipes up to the level maintained in the cooling tower pond.
So when the pump is restarted again, it has to work additionally to “lift” the water from the pond to cooling tower nozzles in addition to working against the frictional resistance in the pipes and associated fittings in the system.
Flow of a condenser water circuit as per ARI standards is considered to be between 3 to 4 GPM/ton
Head is the summation of static head + frictional loss component in the piping
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CHALLENGES ON THE CONDENSER WATER LOOP
PUMP CAVITATION• Always locate the CWP close to cooling
towers.• Ensure sufficient NPSHa• NPSH (Net Positive Suction Head)
available at site has to be kept sufficiently more than the required for the pump duty, by designing the piping system NPSH available is supplied from the system and it is solely a function of the system design on the suction side of the pump
• To avoid cavitation, the NPSH available from the system must be greater than the NPSH required by the pump
• Avoid using high pressure drop strainer, check valve and balancing valve in suction line
• Avoid overhead suction piping
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CHALLENGES ON THE CONDENSER WATER LOOP
AIR ENTRY AT BASIN• Vortex at collection basin is created
when, there is insufficient water level above the collection basin exit for the velocity that the water is exiting
• Facts contributing to formation of vortex:
• Sudden decrease in exit pipe size (suction line) causes the water velocities above the maximum allowable limit, vortex created.
• Over sizing of pumps due to over estimation of frictional losses.
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PIPING SCHEMES FOR CONDENSER WATER
INDEPENDENT CONDENSER & COOLING TOWER
ADVANTAGES• Equipment’s can be of unequal
sizes• Equalization line not required• Controlling and balancing
DISADVANTAGE• High initial cost
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PIPING SCHEMES FOR CONDENSER WATER
INDIVIDUAL PUMP FOR CONDENSER
ADVANTAGES• Lesser initial cost
DISADVANTAGE• Equalization line required• More complicated balance and
controlling• Higher potential of pumps
cavitation Chillers
Condenser Pumps
Cooling Tower Cooling Tower
Equalization Line
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PIPING SCHEMES FOR CONDENSER WATER
INDIVIDUAL PUMP FOR COOLING TOWER
ADVANTAGES• Lesser initial cost• Less potential on pump cavitation
problem
DISADVANTAGES• All pumps and condenser must be
of equal sizes• Balancing and control• Equalization line required
Chillers
Condenser Pumps
Cooling Tower
Cooling Tower
Equalization Line
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PIPING SCHEMES FOR CONDENSER WATER
COMMON HEADER FOR ALL EQUIPMENTS
ADVANTAGES• Lesser initial cost• Easier for equipment maintenance
DISADVANTAGES• All pumps and condenser must be
of equal sizes• Balancing and control• Equalization line required
Chillers
Condenser Pumps
Cooling TowerCooling Tower
Equalization Line
Chillers
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DESIGN CONSIDERATION IN CHILLED WATER DISTRIBUTION
POINTS TO NOTE: It’s always recommended to use more
cooling towers to lower the condenser coil entering temperature which gives better energy performance of the entire plant.
Equalizing lines and baffle plates are to be considered with due care to avoid cooling tower over flow and vortex formation which will adversely affect the performance
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WHAT IS DISTRICT COOLING?
A District Cooling System (DCS) distributes thermal energy in the form of chilled water or other media from a central source to multiple buildings through a network of underground pipes for use in space and process cooling.
DCS eliminates the need for separate systems in individual buildings as the cooling or heat rejection is usually provided from a central cooling plant.
A DCS consists of three primary components: the central plant, the distribution network and the consumer system.
The central plant may include the cooling equipment, power generation and thermal storage.
The distribution or piping network is often the most expensive portion of the DCS and warrants careful design to optimize its use.
The consumer system would usually comprise of air handling units and chilled water piping in the building.
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TYPICAL COMPONENTS OF DISTRICT COOLING PLANT
Chillers Pumps Energy Transfer Stations Pipe Network & Insulation Cooling Towers Make Up Water Systems
For Chilled & Condenser Water
Plant Control And Automation
Metering & Billing
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WHY DISTRICT COOLING?
To outsource operations to specialist companies that can provide the cooling services more efficiently
Environmental policies to reduce air‐pollution, noise pollution, greenhouse gas emissions and to reduce ozone depleting refrigerants
To reduce peak electricity demand in the power grid
More sellable space for the builder
Increased system reliability Less CO2 emissions
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WHY DISTRICT COOLING?
In Building Equipment, Chilled Water Central District Cooling Plant
0,34 kW/kW (COP: 2,9) 0,24 kW/kW (COP: 4,1)*
*Under less then optimal design/operation Source: 2012 ASHRAE Handbook, HVAC Systems and Equipment
Air Coolied, In Building Equipment District Cooling , Elecrical Driven WithTES
0,47 kW/kW (COP: 2,1) 0,20 kW/kW (COP: 5,0)
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CHALLENGES IN DISTRICT COOLING Non existence of dual power tariff.
Shortage in power supply.
Statutory clearances like environmental clearances, NOC’s & Permits etc.
Capital lock up for the DC service provider.
Delay in connecting promised cooling load by the customer.
Metering & billing (Flat‐ Sq. feet based / BTU‐usage based ?).
Poor maintenance of customer side resulting in Low Delta T.
TES water usage has been made mandatory by Governments, but drainage is still a challenge due to high TDS value
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WHAT IS RADIANT COOLING? Bodies of a higher temperature
radiates heat to a body of lower temperature.
Our bodies radiate heat to any surface in line of sight which is cooler than our bodies surface temperature of 29~32 deg C.
WHY RADIANT COOLING? Water can store 3,400 times
more thermal energy per unit volume than air.
This reduces the size of the air system which is only required to dehumidify the space.
In other words, sensible heat load is addressed by radiant system and latent heat load is addressed by Dedicated Outdoor Air System (DOAS)
BENEFITS OF RADIANT COOLING ADVANTAGE 1
Chiller outlet temperature can be 16 deg C instead of conventional 7 deg C – straight away reduction in chiller energy spent.
ADVANTAGE 2
Less energy required to transport waterthan air. Refer below chart.
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RADIANT HEAT TRANSFER
Heat will flow from objects, occupants, equipment and lights in a space to a cooled surface as long as their temperatures are warmer than that of the cooled surface and they are within the line of sight of the cooled surface.
The process of radiant exchange has a negligible effect on air temperature, but through the process of convection, the air temperature will be lowered when air comes in contact with the cooled surface.
TYPES OF RADIANT SYSTEMS
CHILLED SLABS
These deliver cooling through the building structure, usually slabs, and is also know as thermally activated building systems (TABS).
In TABS water pipes are integrated into a concrete slab or a screed in the surface of floor or ceiling during construction.
Water inlet temperature is usually around 14 – 18 deg C and therefore the surface temperature is 17 ‐21 deg C.
Cooling delivered through the floor makes the most sense when there is a high amount of solar gains from sun penetration, as the cool floor can more easily remove those loads than the ceiling. Chilled slabs, compared to panels, offer more significant thermal mass and therefore can take better advantage of outside temperatures swings. Chilled slabs cost less per unit of surface area, and are more integrated with structure.
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LIMITATIONS OF RADIANT COOLING
Condensation caused by humidity is a limiting factor for the cooling capacity of a radiant cooling system.
The surface temperature should not be equal or below the dew point temperature in the space.
An air temperature of 26°C (79°F) would mean a dew point between 17°C and 20°C (63°F and 68°F).
Decreasing the surface temperature to below the dew point temperature for a short period of time may not cause condensation.
Also, the use of an additional system, such as a dehumidifier, can limit humidity and allow for increased cooling capacity. surface.
TYPES OF RADIANT SYSTEMS
COOLING PANELS
Radiant cooling panels are attached to ceilings, or to walls. They are usually suspended from the ceiling, but can also be directly integrated with continuous dropped ceilings. Modular construction offers increased flexibility in terms of placement and integration with lighting or other electrical systems.
Chilled panels are also better suited to buildings with spaces that have a greater variance in cooling loads. Perforated panels also offer better acoustical dampening than chilled slabs.
Ceiling panels are also very suitable for retrofits as they can be attached to any ceiling. Chilled ceiling panels can be more easily integrated with ventilation supplied from the ceiling.
Ceiling panels tend to cost more per unit of surface area than chilled slabs..
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CHILLED WATER DISTRIBUTION IN RADIANT SYSTEMS
From chillers, branch headers are separated to feed individual building loops.
Each individual floor plate or installation will be connected to manifolds which further distributes it to the PEX pipes either buried or fitted on the ceiling.
Each pipe has definite spacing between them to ensure proper heat transfer to the adjoining thermal mass.
Need for temperature regulation of supply chilled water :
1. Maintaining supply temperature above dew point temperature of the conditioned area to avoid condensation
2. To cut off chilled water supply pump / system when zone conditions on humidity and dew point get adverse
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TRENDS IN AIR‐CONDITIONING PUMPS
Pumps with integrated controls, variable frequency drives and sensors that make a more efficient overall solution with smaller footprint.
Smarter way of controlling pumps and intelligent communication possibilities are helping building managers run systems efficiently.
Building information modelling is making it much more easier to build and commission systems the way they were meant to be.
Controlling pumps and pumping systems remotely through remote management services is becoming more and more popular due to lower costs than conventional BMS systems.