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SURVEY OF OUTDOOR AIR CONDMONER NOISE
FINAL REPORT - Revised February 27, 1991
RAC Report # 458G
Report prepared for:
Research and Technology Branch
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Ontario Ministry of the Environment
1 Report prepared by:
J.S. Bradley of the National Research Council Canada
and the
Heating, Refrigerating and Air Conditioning Institute of Canada
1 DECEMBER 1991
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Cette publication technique nest disponible qu'en anglais.
Copyright: Queen's printer for Ontario, 1991
This publication may be reproduced for non-commercial purposes
with appropriate attribution.
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ACKNOWLEDGEMENT AND DISCLAIMER
This report was prepared for the Ontario Ministry of the
Environment. The views and ideas expressed in this report
are those of the author and do not necessarily reflect
the views and policies of the Ministry of the
Environment, nor does mention of trade .names or
1 commercial products constitute endorsement or
recommendation for use. The Ministry, however,
encourages the distribution of information and strongly
supports technology transfer and diffusion.
Any person who wishes to republish part or all of this
report shouted apply for permission to do so to the
Research and Technology Branch, Ontario Ministry of the
Environment, 135 St. Clair Avenue West, Toronto, Ontario,
M4V 1P5, Canada.
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Copyright: Queen's Printer for Ontario
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non-commercial purposes with appropriate
attribution.
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CR5954.2, Revised Page I of 52
Executive Summary This report presents the results of a survey of both
subjective and objective ratings of outdoor domestic air
conditioner noise. The survey was carried out in the
Metro Toronto area, and both subjective and objective
data were successfully obtained for 550 subjects. Subjects
were selected to include the four combinations of low and
high ambient noise level sites with owners and non-
owners of air conditioners. In many cases, air conditioner
noise levels were not substantially higher than existing
background noise levels, making it difficult to obtain
strong relationships between the air conditioner noise
stimulus and subjective responses. Some highlights of
the results include:
(1) In spite of the inherent difficulties described above,
adverse responses were significantly related to
objective noise measures. While there were many
statistically significant relationships between
objective and subjective responses, the variance
explained was often quite small and one should be
careful not to assume these results to be more
precise than is really justified.
(2) Adverse responses were more strongly related to
signal/noise ratios than to the measured noise
levels.
(3) Below 50 to 55 dB(A) (as measured at the property
line), annoyance was not systematically influenced
by air conditioner noise level. Similarly, below a
signal/noise ratio of about +5 dB(A), annoyance was
not related to measured noise levels.
1
(4) At sites with higher ambient noise, subjects were
less annoyed by their neighbours' air conditioner
noise by the amount expected due to the decreased
signal/noise ratio.
(5) Owners of air conditioners were less annoyed by air
conditioner noise by an amount equivalent to
7 dB(A) lower air conditioner noise levels.
(6) The ARI 275-84 prediction scheme was not found to
be particularly accurate. Measured levels close to
the air conditioner source were on average several
decibels lower than predictions. Similarly,
measured values at the facade of the neighbours'
home were on average not predicted well. In most
cases there was a quite large scatter in the
comparison of predicted and measured values.
CR5954.2, Revised Page 2 of 52
....................
...
Table of Contents 1. Introduction ... ... .. .. ........... .. .... ..., . .. 3 1
2. Methodology 4
.
2.1 Experimental Design 4
. . . . . . . . . . . . . . . . . . . . . . . .
2.2 The Questionnaire . . . . . . . . . . . . . . . . . . . . . . . . . .4
2.3 Noise Measurements. .. .. .. .. .. .. .. .. . ... . ... .. .. .. .. .. .. .. .. .. .. .. .. 5
3. The Survey Sample ... 7
.. .. ..
3.1 Acoustical Da.ta. .... .. .. ....... .... .. . . .. .. .. . ... .. .. .. .. . 7
3,2 Survey Data ............. .. .. ... .. .... 11
3.3 Quality of the Data .... ..... .... .13
..
4. Initial Individual Subject Analyses ... .14
..
5. Individual Data - Methods to. .Im..pr o.v.e .C.o.r re.l.a ti.o.n.s .. ... . 17
5.1 Composite Response Scales .... 17
.
5.2 Selecting Data According to Signal/Noise Ratio 18
. . . .
5.3 Signal/Noise Ratio as a Better Predictor 23
. . . . . . . . .. . . .. . .
6. Individual Data and Subject Selection Variables 27
. . . .
6.1 Success of Subject Selection P.ro.c.ed.u.re. ....... ...... 27
. . . . . . . . . . . . .
6.2 Analysis of Variance Results 27
6.3 Influence of Air Conditioder Ownership . .. ... . ... . . . . ... .. .. . 28
..
6.4 Influence of Ambient Noise Conditions 30
.
7. Individual Data a.n.d. N.o.n.-N.o.is.e. P r.ed.i.c.to.r s .. .. .. .. . . .. . . .. . . . . 32
8. Grouped Data . . .35
8.1 Simple Relations with Noise Level Predic..to r.s. . . .. . . .. . . .. .. ....3 5
8.2 Influence of Subject Selection Vari.ab.l.es. . .. .. .. ...... 40
8.3 Influence of Non-Noise Predictors 42
9. Comparisons with the ARI Noise Level Prediction Procedure .43
9.1 Predictions from Manufacturers Ratings . . .. . . . .. . . .. ... . ... .. 4463
9.2 Predictions from Measured Source Levels
. .
9.3 Summary . . . ... .. . .. .. . ... . . ... .. . ... . . . . . . . . . . . . . . 49
10. Conclusions . . . . . . . . . . . . . . . . .50
Appendix 1. The Questionnaire
s
Appendix 2. Statement of Work
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CR59542, Revised Page 3 of 52
1. Introduction This is the final report of a survey of both sound levels
and subjective attitudes to residential air conditioner
noise levels. The work was a joint project of the National
Research Council (NRC), the Ontario Ministry of the
Environment (MOE), and the Heating Refrigerating and
Air Conditioning Institute of Canada (HRAI}. Support for
the field measurements was also provided by the City of
North York, the City of Toronto, Toronto Hydro, the
Ontario Home Builders' Association, Ontario Hydro, and
the Ontario Ministry of Housing. MOE was responsible
for finding appropriate measurement sites and for all field
measurements. NRC planned the experimental design
and carried out all analyses of the data including the
preparation of this report.
'The purpose of the survey was to consider the question of
acceptable limits for outdoor residential air conditioner
noise. The terms of agreement of the contract under
which this work was performed are included in
Appendix. 2. The principal objectives of the project were:
(a) to quantify the relationship between subjective
response to neighbours' air conditioner noise and
the measured noise levels of these air conditioners;
(b) to provide information to support the setting of
acceptable limits for outdoor air conditioner noise
levels;
(c) to examine how local ambient noise and ownership
of an air conditioner influence adverse reactions to
air conditioner noise;
(d) to consider the influence of other non-noise factors
on adverse reactions to neighbours' air conditioner
noise;
(e) to compare measured air conditioner noise levels
with predictions based on the ARI 275-84
procedure.
It was initially planned that all measurements would be
made during the summer of 1989 and that analyses of the
data would be completed in the fall of 1989. The first
measurement phase was not completely successful and a
second phase of measurements was carried outduring the
summer of 1990 at sites in the Metro Toronto area. The
final data set included questionnaire responses along with
air conditioner and ambient noise measurements for 550
subjects. This report describes the analysis of this data.
CR5954.2, Revised Page 4 of 52
2. Methodology It had been suggested that residents in noisier areas
might be more tolerant of noise from their neighbours' air
2.1 Experimental conditioner, and that subjects who owned air conditioners
Design
would be less disturbed by the noise from their
neighbours' unit. The experimental design included a
subject selection procedure that would make it possible to
determine the effects of ambient noise levels and
ownership of an air conditioner on adverse responses to
air conditioner noise.
The goal was to interview a total of 600 subjects from four
equal groups. The groups were to be the four
combinations of high and low ambient noise with owning
and not owning an air conditioner. Thus, it was hoped to
obtain 150 subjects in each of these four groups. Of
course, each subject had to have at least one neighbour
with a central air conditioner or heat pump. Subjects also
had to be at least 18 years of age, and it was hoped to get
an approximately equal number of males and females.
Potential subjects first received an introductory letter
from the Ontario Ministry of the Environment describing
the survey as concerning particular aspects of the 1
neighbourhood environment, and encouraging them to
participate. Shortly after receiving the introductory
letter, subjects were approached by an interviewer, and
an interview was carried out at the convenience of the
subject. No mention was made that the survey concerned
air conditioner noise until after the interview. However,
after a few questions, subjects were asked if any of their
immediate neighbours had a central air conditioner. If
not, the subject was thanked and the interview
terminated.
After the interview was successfully completed,
permission to make noise measurements was requested.
These were made as soon as possible after the completion
of interviews in that particular area. As a final gesture,
each subject was given a thank you letter expressing
appreciation for their help, revealing that the survey was
focussed on air conditioner noise, and giving the names of
the three main sponsoring groups.
2.2 The Questionnaire The questionnaire was administered directly to subjects
in their homes by a trained interviewer. The interviewer
wrote the coded responses on the questionnaire form.
Most responses were in the form of seven-point response
scales, and subjects were shown a response card from
which to select a numerical response. The card included
the integer numbers from 0 to 7; the value "0" was labeled
CR5954.2, Revised Page 5 of 52
1 "Not Applicable", the value "1" was labelled "Not at all";
the value "4" was labelled "Medium", and the value "T'
was labelled "Very". By not labeling intermediate values
of the seven-point scale, it was hoped that subjects would
linearly interpolate between the extremes of the end
values and valid interval scale response data would be
obtained. Where subjects refused to answer particular
questions (e.g. concerning income), a %1" response was to
be entered.
A copy of the questionnaire is included in Appendix 1.
The first two questions in the interview were open-ended
questions about things subjects liked and didn't like about
their"neighbourhood. This gave respondents a chance to
spontaneously mention air conditioner noise without any
prompting by more direct questions. This was followed by
questions concerning how considerate their neighbours
were thought to be, and whether an immediate neighbour
had a central air conditioner or heat pump.
This initial section was followed by the main body of the
questionnaire that included direct questions concerning
how often they heard or were annoyed by various
environmental noises. These included: road traffic noise,
aircraft noise, train noise, and residential air conditioner
noise. This block of questions was repeated four times.
The questions were asked for day- and night-time
conditions as well as for the subject being indoors or
outdoors. This was followed by questions concerning
possible sleep disturbance by each type of environmental
noise.
The final section of the questionnaire gathered the usual
socio-economic information about respondents. Questions
concerned the total family income, the subject's years of
formal education, the subject's age, the number of adults
and the number of young people in each home. They were
also asked- whether air conditioner noise was more
disturbing in a particular room, whether they owned a
central or window air conditioner, and how much extra
they would pay if buying a $2,000.00 central air
conditioner for a very quiet model. The interviewer also
recorded whether the subject was male or female,
whether they appeared to have any hearing problems.
and whether their home was a row house, semi-detached,
or a detached home.
2.3 Noise The noise measurement data were first entered onto
Measurements
sheets attached to the subjects questionnaire responses.
Integrated A-weighted sound level measurements were
