preventive strategy for air conditioning - oisdoisd.brookes.ac.uk/conferences/ukindia/preventive...

“Preventive” strategy for air conditioning- A case for India

Ashok B. Lall, Ruchi ParakhAshok B. Lall Architects,

2B Ramkishore Rd., Civil Lines,New Delhi 110054

Email [email protected]

Preventive Strategy for Air Conditioning – A Case for India


Introduction

The question “is air conditioning necessary?” arises because the sharply rising demand for refrigerant-based air conditioning in emerging economies of the Tropical and sub-Tropical regions of the world is likely to become the single largest contributor to the increasing fossil fuel based energy consumption in buildings.

The widespread adoption of air conditioning – a technological fix for indoor thermal comfort developed in the United States - will be an automatic consequence of economic advance and the rising aspirations of the developing world..

In a predominantly hot climate refrigerant based air conditioning becomes the default “total solution” for assured thermal comfort in buildings.

Rising demand

Popular assumption

Default position


The economy is shifting towards services located in urban centres with a growing upwardly mobile middle class. It is predicted that by 2020 about 40% of India’s population will be living in cities, as against 28% today.

Context- Urbanisation and the rise of the middle class


The Context:Spiraling urban growth

In the next five years

13 million m2

Retail space in malls

19 million m2

Commercial space

20 milliondwelling units

Housing

50,000 rooms

Hotels Retail space in malls

Agriculture30.7%

Transportation2.8% Residential

23.4%

Commercial6.6%

Industrial36.5%

Sectoral energy consumption

Statistics released by the Bureau of Energy Efficiency, whose projections for anticipated growth in energy demand related to buildings clearly show the dominance of residential buildings compared to other sectors of building construction


Energy Consumption in commercial and residential buildings

Commercial buildings 33 billion units

Residential buildings 116 billion units

At present air conditioning accounts for a small fraction (7%) of energy demand in housing, whereas for commercial buildings air conditioning accounts for 30% of energy consumed.

In the case of commercial buildings the threshold into air conditioning dependency has already been crossed.

In the case of residential buildings there is still the opportunity and potential of prevention

Lighting32%

Others8%

HVAC60%

TV4%

Refrigeration13%

EV Cooler4%

Fans34%

Lighting7%

A/C28%

Others10%


Comfort Technology Ceiling Fan Evaporative Cooler Air-conditioner

Power requirement for 12 sqm. Floor area 80 Watts 120 Watts 1000 Watts

TREND

CRITICAL TRANSITION

Need for insistence on high efficiency

As one shifts from circulating fans and evaporative coolers to an air conditioner the peak demand of electricity increases by six to ten times per unit of conditioned space – an increase of about 90 watts per sq. metre of conditioned space.

This is what we seek to prevent.


This is a mere tip of the iceberg if we were to also take into account the existing housing stock, and future growth that might plateau by 2020.

20 million dwelling units

10 sqm Floor Area/ dwelling unit(for air conditioning)

@ 90 watts/ Sqm

18000 MWAdditional summer peak load

Next 5 years’ projection


AHMEDABAD(HOT DRY)

NEW DELHI(COMPOSITE)

BANGALORE(TEMPERATE)

CHENNAI( WARM HUMID)

The projected expansion in built space will occur in the major urban centres of the country,

Most of which are located in the hot climate zones with the notable exception of Bangalore.

Toward assessing the potential impact of the preventive strategies nationally, four big cities are selected:

New Delhi Ahmedabad Chennai Bangalore

Methodology


Aspirational comfort!

“Will do”Basic comfort

Thermal comfort or expectations with regard to thermal comfort are, in a substantial measure, culturally directed and are adaptive as well as variable.

“Feeling cool”(bordering on feeling chilly)

High comfortNicolº C

Nicolº C – 3 º C


Aspirational comfort!

“Will do”Basic comfort

“Feeling good”Reasonable comfort

Aspirational comfort asks for somewhat cooler temperatures than basic comfort.

Nicolº C – 1.5 º C

Nicolº C


Assumptions

Method of building constructionThe structural system and basic infill of buildings, has become more or less uniform.

It has a masonry envelope of bricks or concrete block of approximate 220 mm thickness, with a 120 to 150 mm thick reinforced concrete roof, topped with high mass roofing treatments.

Low rise high density development- A pattern that will progressively become the norm across the country.

New Delhi Chennai

Density: A pattern of development that would have an average of 4 storey buildings while occupying one third of the ground surface.

New Delhi

Bangalore


31st May

20222426283032343638404244

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Time

Tem

pera

ture

DBT (Dry bulbtemperature)

WBT (Wet bulbtemperature)

31st May

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Time

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Tba (Predicted temp. for'basic' comfort)

Tgo (predicted temp. for'good' comfort)

31st May

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Time

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pera

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Tmass (inside temp. due toinsulated/mass buildingenvelope)




31st May

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Time

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Tev (Temp. ofevaporatively cooled air)




Methodology

31st May

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Time

Tem

pera

ture

DBT (Dry bulb temperature)


Tev (Temp. of evaporativelycooled air)

WBT (Wet bulb temperature)



ET (Effective temp combiningTmass + Tev)

31st May

20222426283032343638404244

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

Time

Tem

pera

ture


Tmass (inside temp. due toinsulated/mass buildingenvelope)Tev (Temp. ofevaporatively cooled air)




ET (Effectivetemp.combining Tmass +Tev)CET (Corrected effectivetemp taking fanned airspeed of 2m/s)

First – Assuming a high mass building envelop insulated from the outside, the indoor dry bulb temperature (or theoretical internal radiant temperature) resulting from the decrement factor and the thermal time lag (Tmass), is plotted.

Second – The temperature of evaporatively cooled air (Tev) which would be flushed through the building is plotted assuming an efficiency of 70% with respect to wet bulb temperature.

Third – The effective temperature that would be felt on combining the effect of radiant temperature modified by evaporatively cooled air (ET) is plotted assuming that it would lie half way between Tev and Tmass.

Fourth – A circulating fan is introduced and a corrected effective temperature (CET) for a wind speed of 2 metres per second, applied to the effective temperature of the Third step, is plotted

A case of New Delhi


NEW DELHI

31st May

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Time

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ture

30th June

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Time

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31st July

20

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2628

30

3234

3638

40

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31st August

182022242628303234363840

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AHMEDABAD

31st May

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CHENNAI

31st May

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30th June

20222426283032343638

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31st July

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31st August

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BANGALORE

30th June

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31st July

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31st August

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31st May

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30th June

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31st July

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31st August

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Time

Tem

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ture

DBT

WBT

Tba

TgoCET @2m/s

LegendResults are plotted for each city for the last day of the four hot months


Cooling degree hours (cdh)

Cooling degree hours not met by passive low energy means

Effectiveness of the passive/ low energy strategies is assessed by the cooling degree hour method.


ANALYSIS OF PASSIVE LOW ENERGY STRATEGY PERFORMANCEvis-à-vis COOLING DEGREE HOURS (cdh)

NEW DELHI

Cooling degree hrs (cdh)

cdh met by passive low energy means for "good" comfort

% of cdh achieved

cdh not met by passive low energy means

% of discomfort cdh

Months

May 5524 5301 96.0 223 4.0

June 5184 4916 94.8 268 5.2

July 3515 3218 91.6 297 8.4

August 3168 3118 98.4 50 1.6

Total 14223 13385 94.1 838 5.9

AHMEDABAD

Months

May 3695 3671 99.4 24 0.6

June 2664 2547 95.6 117 4.4

July 2120 1922 90.7 198 9.3

August 2064 2064 100.0 0 0.0

Total 8479 8140 96.0 339 4.0

New Delhi- “Good” comfort is not achieved during the peak humid season of July. The little discomfort during May and June mornings can be overcome with night ventilation. Only about 6%of cooling-degree hours for May to August remain unaddressed

Ahmedabad- There is discomfort during July when the humidity builds up. Only 4% of the cooling degree hours for May to August remain unaddressed.


ANALYSIS OF PASSIVE LOW ENERGY STRATEGY PERFORMANCEvis-à-vis COOLING DEGREE HOURS (cdh)

CHENNAI


cdh met by passive low energy means for "good" comfort

% of cdh achieved

cdh not met by passive low energy means

% of discomfort cdh

Months

May 2941 2893 98.4 48 1.6

June 3726 3495 93.8 231 6.2

July 2994 2755 92.0 239 8.0

August 2046 2046 100.0 0 0.0

Total 9661 9143 94.6 518 5.4

BANGALORE

Months

May 1466 1466 100.0 0 0.0

June 1131 1113 98.4 18 1.6

July 1088 1060 97.4 28 2.6

August 477 477 100.0 0 0.0

Total 3685 3639 98.8 46 1.2

Chennai - “Good”comfort is not achieved during July days although this is by a mere 0.5 degC. The minor discomfort during the nights of May and June can be overcome by night ventilation

Bangalore -“Good”comfort is achieved throughout the year by the passive low-energy strategies


New Delhi

0

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May June July August

Months

Coo

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ours

Ahmedabad

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Months

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Chennai

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Bangalore

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Months

Cool

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ours


cdh not met by passive low energymeans

Legend

Results and Findings


Further steps

About 80% of the urban population of the country is located in the composite and hot-humid climate regions.

Population distribution


Rs. 10, 000/m² Rs. 10, 500/m²

Rs. 11, 000/m²

An additional 10% spending over the civil work cost of a simple building could attain the theoretical potential of passive and low-energy strategies toward comfort, reaching 95% satisfaction!

On improvement of building envelope

On adding evaporative cooling/ ventilation system

Capital costs for “good” comfort

Standard construction

Evaporative cooler


Rs. 12, 250/m²

If an air conditioner were to be installed to ensure 100% satisfaction, because 95% satisfaction is not acceptable, it would cost Rs.1750 per sqm of conditioned floor area. This is a high price to pay for that extra bit of comfort.

Air conditioner

Capital costs for “good” comfort

House dependent on window air conditioners


MAY

AUGUSTLall Residence


Conclusions

If the standard of an adaptive “good” comfort is considered to meet the aspirations of the bulk of the urban populations in India, then passive low-energy techniques can dramatically raise the threshold of transition to air conditioning.

Substantial periods of comfort are obtained by shading, insulation, thermal mass, night ventilation and ceiling fans.

The short periods when low- energy techniques fall short of delivering comfort happen to be due to high humidity rather than high temperature. This shortfall hardly warrants the cost of the considerably more expensive systems of conventional air conditioning on both counts – installation cost as well as running cost.

This points toward investigating alternative techniques for dehumidification for these short periods which are energy efficient as well as low cost. Conceptually, what is needed is a method of bringing relative humidity down to 70% when temperatures rise above 29 deg C.Such a technique could be used in conjunction with air movement to achieve comfort.

In the dry seasons evaporative cooling with air movement provides comfort.


On the basis of this rough science the theoretical potential of passive low-energy techniques looks encouraging.

There is a strong case for examining this potential more precisely by dynamic thermal simulation.

The greater issue of turning around building design and construction practices to incorporate them in robust and reliable ways still remains to be addressed.

When one considers the need to improve the existing building stock, however, the challenge is greater.

Today, as we stand at the threshold from which a wide spread transition to refrigerant air conditioning is likely to occur bydefault. The urgency to build and execute a preventive strategy can hardly be overstated.

I propose that this rough science be verified and its potential developed urgently with proper scientific research.

Conclusions

It is never too late!

preventive strategy for air conditioning - oisdoisd.brookes.ac.uk/conferences/ukindia/preventive...

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