Welcome to an interactive

session on

HVAC System level

design & efficiency.

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Contents

• Introduction

• Basics of R & AC

• Efficiency considerations in system design

• Sizing guidelines

• Types of conventional equipment

• Efficiency enhancing supplement

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Introduction

• Energy Efficiency in HVAC system of any

application , be it a Commercial or an

Industrial or a Residential , is a result of

conscious decision to be Energy Efficient

during ;

• Design

• Engineering

• Installation & Commissioning

• Operation & Maintenance

Today ,we will touch upon Design and Engineering

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Basics of R & AC

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Efficiency expression

• For the refrigeration cycle it is expressed in terms of Coefficient of Performance (CoP).

• CoP = Net Refrigeration effect/ Power input

in consistent units under specific operating condition. It could be applied to complete system also. Higher the CoP , better is the efficiency.

• IPLV is integrated part load value which is a single number figure of merit , based on part load CoP or EER or Kw/ TR. It is worked out on the basis of weighted operation at various capacities (100,75,50 and 25 %)

• IPLV = 0.01A+0.42B+0.45C+0.12D where A is CoP at 100 % and so on.

• Factors are based on weighted average of the most common building types and operation, using average weather in 29 US cities , with or without air side economizer.

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Conventional AC & R equipment

• Step # 3 is to produce SYSTEM Capacity in the most suitable & Energy Efficient manner.

• Today , we will touch upon conventional equipment for buildings.

A)Central plant , Chilled water ;

1. Centrifugal, 300 TR plus , water cooled, CoP >6

2. Screw , 50TR or more , water cooled, CoP>5.4

3. Scroll , 10TR or more , water cooled , CoP>4.7

4. Recip. , 10TR or more , water cooled , CoP>4.1

5. Absorption 50TR or more , water cooled , CoP is low but works on waste/recovered/Solar heat .

• These chillers will be connected to AHUs at zone level. Controls on AHUs play a vital role in determining Chiller energy performance.

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Continued….

B)Variable refrigerant flow , air cooled, Dx type, CoP is NOT specified in ECBC-2007.

C)Duct-able or packaged units , water or air cooled , Dx type.

D)Unitary , air cooled, Dx type , Star labeled.

E)Condensing units with AHU , custom made , air cooled , Dx type .

F)Self contained roof tops , air cooled , Dx type . These are available with air economizer.

G)Evaporative cooling based equipment , custom made , suitable for dry ambience. Air can not be re-circulated.

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Plant sizing guidelines

• The total System capacity ( High side Chiller or Dx) could be divided

in to 2 x 50 % or 3 x 50 % ( one stand by ) or more suitable steps

depending on the application and size.

• Condenser and Chilled water pumps sizing should be preferably

one per chiller . Only one stand by if pumps are two or more. Pump

curve should accommodate full and part load flow rate at respective

pressure. Throttling of flow should be minimum. Do not go below

minimum flow specified by chiller manufacturer.

• Cooling tower could be one per chiller if space permits. It will save

lot of fan power if one chiller is put OFF. VFD for fan is advisable for

motor HPs higher than 7.5. If two speed fan is selected then ensure

enough static pressure at lower speed. Select as minimum approach

as possible. See table on next slide.

• All air handling units (AHUs) should be sized for the PEAK load of

the zone . DD fans does not have transmission loss. Fan curve

should accommodate full and part load flow rate at respective

pressure. Throttling of flow should be minimum.

• Use Energy Efficient pumps , fans and motors.

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WBT ApproachBasin water

temperature

Cooling

tower

fan power

Chiller

capacity

Chiller power

consumptionTotal Ikw

Specific

power

consumption

deg F deg F deg F Ikw TR Ikwchiller +

cooling towerIkw/TR

1 82.4 3.6 86 5.2 147.8 101.3 106.5 0.721

2 82.4 5.1 87.5 3.9 146.1 103.3 107.2 0.734

3 82.4 6.6 89 3.5 144.7 104.9 108.4 0.749

Note : 1 Chilled water temperature is same for all three. (45 deg F outlet)

2 Condenser & chilled water flow rates remain same for all three conditions.

Effect of approach on power consumption

Sr.

No.

Supplementary equipment

• Variable frequency drive

• Energy recovery ventilator

• Air economizer

• Superheat recovery

• Thermal storage

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Variable frequency drive

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Energy recovery ventilator

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Air Economizer

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Superheat recovery

• Refer refrigeration cycle.

• Also refer Clause # 6.2.1 of ECBC 2007 – solar

water heating or heat recovery for residence,

hotels and hospitals.

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Chiller capacity , TR 144.7

Child water in/out temperature 12/7 ⁰c

Condenser water in/out temperature 32/37 ⁰c

Chiller input power , Kw 104.9

CoP of chiller 4.84

Hot water flowrate 2.8 m³/hr

Hot water temperature difference 25 ⁰c

Heat recovery 82 KW

CoP with heat recovery 5.62

Superheat recovery from discharge gas

Solar water heating for guest

rooms, restaurant and wash rooms

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Thermal storage

• It is useful to cater to the load which is way higher than average load , as discussed. System capacity and capital cost increases considerably due to such load.

• Thermal storage is based on Latent heat of fusion or Sensible Cooling . Usually latent heat is preferred due to half the size . A 100 TRHr latent storage needs approximately 7 M3 space as compared to 13 M3 for sensible.

• Coolness is stored ( Charging) in nodules in an insulated tank during less tariff time . Coolness is discharged when required over and above the system (Chiller ) capacity. Thus PEAK load is catered to using smaller System Capacity.

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Continued…..

• Advantages are ;

1. Maximum demand (KVA ) and associated costs reduce.

2. System capacity & Capital cost reduce if planned from beginning.

3. Useful if load is not coincident with energy source.

4. Extends capacity of existing system for expansion of the project.

• Thermal storage system may be considered Energy Efficient after calculating Kw/ TR for actual operating condition. It may happen that Kw/TR is higher which is compensated by lower power tariff.

• It needs considerable design & engineering ( of piping ,valves & controls ) , operation and maintenance efforts.

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Thank you.

www.energyca.in

info@energyca.in

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