Energy and Buildings, 17 (1991) 63-74 63

Analysis of the energy performance of office buildings in Montreal in 1988

R a d u Z m e u r e a n u and P a u l F a z i o Centre for Building Studies, Concordia University, Montreal, Que., H3G ]M8 (Canada)

(Received December 7, 1989; accepted May 13, 1990; revised paper received July 20, 1990)

A b s t r a c t

This paper presents the energy performance of office buildings in Montreal based on a survey of 68 buildings (2.5 million square metres). The results indicate an average annual normalized energy consumption of 502.2 kWh/(meyr) and an average annual normalized energy cost of 19.5 $/(m2yr). The electricity represents 68% of consumption and 73% of cost, while the oil and gas each represent 15% of consumption and about 7% of cost. The energy signatures are then developed using the utility bills and the weather data, thus adding information to the overall pattern of energy performance. The analysis indicates a large potential to improve the energy performance of office buildings in Montreal. It also shows that buildings built after 1970 use less energy, but in terms of energy cost there is not a significant difference between old and new buildings.

I n t r o d u c t i o n

Although the office buildings are an impor tan t c o m p o n e n t in the non-resident ia l building s tock in Montreal, and represen t a major target in energy conserva t ion policies, a clear pic ture of their energy pe r fo rmance in this par t icular locat ion is no t available. Two surveys were carr ied out in Montreal, in 1979 by the Building Owners and Managers Associa t ion (BOMA) on 19 buildings, and in 1987 by the Bureau de l 'Efficacite Energe t ique on 24 buildings [1], with the only objective to define the average energy consumpt ion . For compar i son reasons, these values are p resen ted in Fig. 1 a long with results f rom other surveys pe r fo rmed in the U.S.A. and Canada, which were selected to cover the last decade. As these values are not normal ized to a c o m m o n base, due to the lack of required information, and because the sam- ples differ f rom one survey to another , this Figure only shows the genera l pa t tern of the energy consumpt ion . One can not ice an im- por tan t reduc t ion of the average energy con- sumpt ion in Montreal, which in 1986 was equal to the average of office buildings in the U.S.A. (388 kWh/m2yr) . There is still a large gap

be tween the average energy pe r fo rmance of

the office buildings and that of the energy-

efficient buildings.

It is wor th ment ioning the detailed moni-

tor ing of the energy consumpt ion carr ied out

in some o ther buildings, [ 1 2 - 1 4 ] , which can

provide useful informat ion about the disag-

gregat ion of the energy use, and about the

part icular opera t ing condi t ions of the systems. However, this type of survey is feasible only for a small number of buildings. When the

objective is to define the energy pe r fo rmance

of office buildings in a large city, such as

Montreal, the major source of informat ion re-

mains the utility bill. Hence, the analysis should not be limited to the average energy con- sumpt ion or cost, but ex tended to all derived informat ion f rom the utility bill. An elaborate

analysis of these data reveals some individual character is t ics of each building related to its cons t ruc t ion and operat ion, which adds to the picture of the energy per formance . To follow this idea, a survey of the energy pe r fo rmance of the office buildings in Montreal was recent ly carr ied out by the Centre for Building Studies,

0378-7788/91/$3.50 © Elsevier Sequoia/Printed in The Netherlands

64

800

70<3

6 0 0

500

4 0 0

500

200

I00

Energy consumption ~_Wh/m2/Yr~ • EEB = Energy - Eff icient Building

• Vancouver [2] • Ca gory [2]

Montreal

/ Ontario~ Alberta, Manitoba, Brit ish

Columbia [ 2 ]

I

1979

• Canada [4]

• U,S.A [6] • .,...U.S.A LSJ "'Montreal ~I]

/ r:\ • [ • x

EEB EEB EEB EEB EE8 Austral ia [ 9 ] Canada [ 3 ] U.S.A [5] At lant , a U.S.A [7 ] Edmonton [11]

I I I I I Dayton FI,O] i I 1980 1981 1982 1983 1984 1985 1986 1987

YEAR

Fig. 1. Comparison of average site energy consumption for office buildings in the U.S.A. and Canada. These values are not normalized for operating or weather conditions.

Concord ia Universi ty, in co l labora t ion with the Downtown Energy F o r u m p r o g r a m m e and the Bureau de l 'Efficacite Energe t ique de Quebec [15]. The objec t ives were the following: - - to define the pa t t e rn of ene rgy use in office bui ldings in Montrea l in 1988;

- to deve lop a detai led da ta base , useful at different levels of the dec i s ion-making p rocess ;

- to give to the bui lding des igners the t a rge t va lues of the ene rgy use for new or r e n o v a t e d buildings;

- - to aid the bui lding owners and m a n a g e r s to locate thei r bui ldings into the overal l p ic ture of the office bui ldings in Montreal , and then to look for poss ib le i m p r o v e m e n t s of the ene rgy p e r f o r m a n c e .

The initial source of in fo rmat ion for se lec t ing the s amp le bui ldings was the " M o n t r e a l O ~ c e S p a c e D i r e c t o r y -- 1989" pub l i shed by the Building Owners and Managers Associa t ion (BOMA) of Montrea l Inc. After a p re l iminary t e l ephone survey, a n u m b e r of 128 office build- ings were def ined as target , and then 77 le t ters were mai led to expla in the p u r p o s e of the su rvey and ask ing for acces s to the requ i red da ta (May 15, June 9, June 15 and July 31).

Two or th ree weeks af ter each mailing, the t e a m m a d e phone calls to a r r ange a p p o i n t m e n t s

with the peop l e involved in the bui lding man- agemen t , ope ra t ion a n d / o r a ccoun t s depar t - ments . About 400 phone calls were m a d e dur ing this s tage and 45 peop le a c c e p t e d to co l labora te in the survey, which r e p r e s e n t s a coefficient of a c c e p t a n c e of abou t 58%.

It is in teres t ing to note the r ea sons why 32 peop l e did not par t ic ipa te : -- no answer to the le t ter and to the phone calls (8); - no in teres t in the su rvey (7); - no t ime for interview and /o r re lease da ta (6); -- new building or new owner of the building, hence the utility bills for the ent i re year were not avai lable (5);

- - building was sold (4); - no approva l f rom lawyer to re lease the requi red in format ion (1); - utility bills could not be p rov ided by the owner , s ince the t enan t s were direct ly pay ing for hea t ing and electr ic i ty (1).

The ave rage dura t ion of the in terview which fo l lowed was 1 5 - 2 0 minutes . 95% of those in terv iewed p rov ided acces s to the month ly utility bills, while the r emain ing 5% gave only the annual ene rgy cos t a n d / o r annual ene rgy consumpt ion . Finally, the in format ion was col-

l ec ted for 74 bui ldings out o f 128 (58%), but 6 we re e l imina ted for insufficient data. The ra te of o c c u p a n c y for t hese bui ldings e x c e e d e d 90%.

The in fo rma t ion f r o m the ques t ionna i res and f rom the utility bills was p r o c e s s e d , and at p r e sen t the da ta ba se con ta ins for each bui lding the p a r a m e t e r s l is ted in Table 1.

Many o the r p a r a m e t e r s can be inc luded in the da t abase such as ma jo r p r o c e s s load, type of l ighting sys tem, schedu le of ma in t enance , qual i ty of i ndoor env i ronmen t , or ope ra t i ng p a r a m e t e r s of HVAC sys tems . However , the au thor s l imited the ex ten t of the ques t ionna i re , t ak ing into a c c o u n t the difficulties in col lec t ing da ta and the r e s o u r c e s a l loca ted to this first survey. Fu tu re w o r k will include m o r e deta i led in fo rmat ion re la ted to the bui lding opera t ion .

The s a m p l e is found to be r ep re sen t a t i ve of the ent i re bui lding s tock in Montreal , as it cover s each p a r a m e t e r such as yea r of con- s t ruc t ion (Fig. 2), t ype (Fig. 3), c lass (Fig. 4),

TABLE 1. List of parameters in database

Year of construction Building type Building class Gross rentable area Floor-to-floor height Percentage of exterior shading, due to other buildings Glazing type Average percentage of glazing Number of operating hours per day for HVAC and lighting

systems Type of HVAC system Annual electrical, gas, oil, s team and total energy consump-

tion (kWh) Annual electrical, gas, oil, s team and total energy cost Type of fuel Percentage of electrical energy use from the total energy

use Percentage of electrical energy cost from the total energy

cost Average electrical demand (W/m e floor area) Index of energy consumption (ECON) (kWh/(m 2 yr)) Index of energy cost (ECOS) ($/(m 2 yr))

~ 9

3 iiiiiii 1900 1920 1940 1960 19BO 2000

Year of construc?iorl

Fig. 2.Number of sample buildings by year of construction.

65

4 0

:::::::::::::::::::::::::::::::::::::::: :i:i:i:i:i:~:K:.'~:i:i:i:!:!:!:!:!:!::':~ ::::::::::::::::::::::::::::::::::::::::

20 :::::::::::::::::::::::::::::::::::::

:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:. ,o :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

0 I 2 3 4

Building type

Fig. 3. Number of sample buildings by type (1 - office building with retail store, 2 - office building with garage, 3 - office building without a garage, with surface area greater than 7435 m e, 4 - office building without a garage, with surface area less than 7435 me). Garage areas are not included in the gross rentable areas.

40

IO

O

AA A B C

Building closs

Fig. 4. Number of sample buildings by class. BOMA has the following classification; AA= a very new and modern building incorporating the latest in environmental archi- tecture, located in a prime location, and having the highest occupancy rates; A= a relatively new building in a prime location, with high occupancy rates and highly competitive rental rates; B = a n older building renovated to modern standards in a prime location, and with high occupancy rates; a new building in a non-prime location; C = a n older, unrenovated building in fairly good condition; moderate to low rental rates; good occupancy, though possibly slightly lower than city average.

4 0 . . .

[, ;~:i.i 20 tt :.~!:!

Io ::'::;i

. . . .

0 I 2 3 4

Gross rentable orea ( IO0,O00m 2)

Fig. 5. Number of sample buildings by gross rentable area.

gross ren tab le a r ea (Fig. 5), n u m b e r of f loors above g r o u n d (Fig. 6), and fuel type (Fig. 7). The f r equency indica ted in F i g s . 2 - 7 r e p r e s e n t s the n u m b e r of bui ldings for a pa r t i cu la r cat- egory. The to ta l g ross r en tab le a rea of the s a m p l e bui ldings is a b o u t 2.5 mill ion m 2, and r e p r e s e n t s a b o u t 50% of the to ta l r en tab le a rea in Montreal .

As the utility bills indicate the gas con- s u m p t i o n in m 3, and the oil c o n s u m p t i o n in

66

o IO 20 5o 4o 50 60 Number of floors above ground

Fig . 6 . N u m b e r o f s a m p l e b u i l d i n g s b y n u m b e r o f f l o o r s

a b o v e g r o u n d .

30

25 ".'.~:i:i:i:-:i:~:~:i:~:i:i:~:'

2o ::::::::::::::::::::::::::::::::::::

,o ~ii!.-".."iiii.-:.;ili~i!i!.':.."iiii s ~i::::~!iiiiiii::ili::::i~!i!} 0 :':':':':;;'~';i':':':':':':':': ..............

E E+G EtO E+S E+G*O Type of fue~

Fig. 7. Number o f sample buildings by fuel (E - electricity, G - g a s , O - oil , S - s t e a m ) .

litres, the calcula t ion of the site ene rgy con- sump t ion in equivalent k w h for gas, oil and s t e a m was p e r f o r m e d us ing an ave rage effi- c iency of the hea t ing p lant of 70%, and the fol lowing hea t ing va lues of fuels: 37 .89 MJ/ (m 3 gas) and 39.0 MJ/(L oil).

The indices of the ene rgy c o n s u m p t i o n (ECON) and the ene rgy cos t (ECOS) can be used by the bui lding owners and m a n a g e r s for c o m p a r i s o n pu rposes , to loca te thei r bui lding with r e spec t to s imilar s pace s in Montreal . These are the actual energy c o n s u m p t i o n and cost. However , for a co r rec t c o m p a r i s o n of the ene rgy p e r f o r m a n c e of two buildings, the ca lcula t ions m u s t be p e r f o r m e d us ing c o m m o n opera t ing condi t ions. Therefore , the normal- ized ene rgy p e r f o r m a n c e is ca lcu la ted as fol- lows:

NECON = ECON Nref/N

NECOS = ECOS Nrey/N

where

NECON = normal ized ene rgy c o n s u m p t i o n (kWh/(m2yr)

N E C O S = n o r m a l i z e d ene rgy cos t ($/(m2yr))

ECON = ene rgy c o n s u m p t i o n (kWh/(m2yr) )

E C O S = e n e r g y cos t ($/(m2yr))

N = actual n u m b e r of ope ra t ing hour s pe r day

Nr~f = re fe rence n u m b e r of ope ra t ing hour s pe r day.

The m o s t f requen t n u m b e r of ope ra t ing hour s (mode) is 16 hours /day, while the ave rage is 15.4, and the med ian is 15.5. Therefore , the r e fe rence n u m b e r of ope ra t ing hour s Nref is se lec ted to be 16 hours /day.

This p a p e r a t t e m p t s to define the pa t t e rn of the ene rgy p e r f o r m a n c e of office bui ldings in Montrea l in 1988, b a s e d only on the in fo rmat ion f r o m the utility bills and f r o m the ques t ionna i res c o m p l e t e d dur ing the survey.

2. A n n u a l e n e r g y p e r f o r m a n c e

The ave rage ene rgy p e r f o r m a n c e of the entire s amp le can be s u m m a r i z e d as follows: - annual ene rgy c o n s u m p t i o n = 4 5 5 . 3 k W h /

(m2yr); - normal ized annual energy c o n s u m p t i o n

= 502.2 kWh/(m2yr) ; - annual ene rgy c o s t = 17.9 $/(m2yr); - normal ized annual energy c o s t = 1 9 . 5 $/

(m2yr). Other s tat is t ical m e a s u r e s of the ene rgy per-

f o r m a n c e of the entire s a m p l e are given in Table 2. One can obse rve tha t the value which occu r s m o s t f requent ly in the s a m p l e is abou t 318.9 kWh/(m2yr ) for ac tual ene rgy use and 363.5 kWh/(m2yr) for normal ized ene rgy use.

The ene rgy c o n s u m p t i o n of bui ldings type 1 (with retail s tore) and 2 (with ga rage) are not significantly different f rom the ave rage of the entire s amp le (Table 3), while for the office bui ldings wi thout ga rage ( types 3 and 4) the d i f ferences are larger (be tween - 1 7 . 4 % and + 10.4%). The effect of the building type on the ene rgy cos t is different, as the first two building types show differences f rom the av- e rage cos t be tween - 1 2 . 8 % and + 2 1 . 8 % , while for the office bui ldings wi thout ga rage the d i f ferences are smal le r (be tween - 7 . 3 % and +6 . 1%) . In the fol lowing Sect ions, the effect of s o m e p a r a m e t e r s , re la ted to the build- ing cons t ruc t ion and opera t ion , on the nor- mal ized ene rgy p e r f o r m a n c e is d iscussed.

2.1. Year of construction The first impre s s ion is tha t the old bui ldings

p e r f o r m as well or as bad as the new ones (Fig. 8). However , the s amp le inc luded three ve ry r ecen t buildings, where s o m e work was carr ied out dur ing the yea r of analysis, and if these bui ldings are el iminated, then one can obse rve a dec rease of the ene rgy used in offices

67

TABLE 2. Statistical measures of the energy performance of office buildings in Montreal in 1988

ECON NECON ECOS NECOS (kWh/(m'~yr)) (kWh/(m2yr)) ($/(m2yr)) ($/(m2yr))

Average 455.3 502.2 17.9 19.5 Median 406.5 443.8 17.1 17.9 Mode 318.9 363.5 13.6 17.9 Standard deviation 166.0 212.8 8.4 9.7 Minimum 251.4 185.7 6.6 6.9 Maximum 938.3 1134.9 60.5 60.5

TABLE 3. Average energy performance of each building type

Sample ECON NECON ECOS NECOS size (kWh/(m2yr)) (kWh/(m2yr)) ($/(m~r)) ($/(m2yr))

Type 1 33 461.2 510.3 15.6 17.2 Type 2 20 453.6 492.0 21.8 23.3 Type 3 7 376.3 471.7 16.6 20.4 Type 4 8 502.7 521.5 19.0 18.7 Entire sample 68 455.3 502.2 17.9 19.5

( X I00) ._~

12 E ~ A io

~ \ 8

~ ~: 6

~ 2 E

1900

(a)

I

1920

|

- . . . . - . . : .. WO %. ,-, •

I I J

1940 1960 1980

Yeor of cons t ruc t i on

]

2OOO

9 0

§ oo

E 4 0

:~ 3 0 " " ,i " • . , " ' : . ": :.:. .~" ;~ 0 I I I i "

1900 1920 1940 1960 1980 2 0 0 0

C O ) Year of construction

Fig. 8. (a) Normalized energy consumption vs. year of construction. The actual energy consumption is corrected to take into account the same number of operating hours per day. Co) Normalized energy cost vs. year of con- struction. The actual energy cost is corrected to take into account the same number of operating hours per day.

built after 1970. The differences between the patterns of the energy consumption (Fig. 8(a)) and of the energy cost (Fig. 8(b)) are due to the type of fuel used in these buildings. The cost for electricity includes the energy con-

sumption, the demand and eventually the pen- attics for exceeding the subscribed demand, while the cost for gas or oil includes only the consumption. As one can observe in Fig. 9, the offices built after 1970 use more electricity and less of other sources of energy, the ratio electrical-to-total energy varying between 0.6 and 1.0, while for the older buildings this ratio takes values between 0.2 and 0.6. Therefore, the most recent buildings use less energy, but because they have electricity as the main source, the energy cost is not different from that of old buildings.

2.2. Gross r e n t a b l e a r e a The small office buildings present a large

variation of energy performance, because they are mainly envelope-load-dominated buildings (Fig. 10). In the case of large office buildings, which are internal-load-dominated (lighting, equipment) buildings, the size plays a small

I .... i .... 0.8

0 . 6 • • ° ° ' " -

o A ° ° , -. ~ o.4 - ' " o • ~ 0 .2

1900 1920 1940 1960 1980 Year of c o n s t r u c t i o n

2 0 0 0

Fig. 9. Electrical-to-total energy use ratio vs. year of construction.

68

( X nO0)

12

E

x

"6 E

(a)

10

8

6 :.:'..: . .

4 b," . : ...o :"

2

0

0

I I I

L 2 5

Gross ren tab le area (100 ,000 m 2)

~ . . 4 0 a~ E

~' 20 "...':.

0 I I I 0 I 2 5

(b ) Gross ren tab le area ( l O 0 , O 0 0 m 2)

Fig. 10. (a) Normal ized ene rgy c o n s u m p t i o n vs. g r o s s r en tab le area. (b) Normal ized e n e r g y cos t vs. g r o s s ren tab le a r e a .

8 0

9 o

o

o i

o

60

4O

2O

0 1900

I I I I

1920 1940 ~960 1980 2 0 0 0

Yeor of const ruc t ion

Fig. 11. Glazing-to-wall rat io vs. yea r of cons t ruc t ion .

role. The energy performance of the largest office buildings are close to the average of the entire sample.

2.3. Percentage of exterior glazing Three distinct periods in the design of the

exterior envelopes can be observed in Fig. 11: - before 1960, when the average percentage of glazing was between 20% and 40%;

- between 1960 and 1975, with glazing of 3O-70%; - after 1975, with glazing of 20-50%.

This pattern cannot be directly related to the energy performance, because other factors such as internal loads, air infiltration or thermal control play an important role.

2.4. Type of glazing The survey indicated that 22.2% of the sam-

ple buildings still have single glazing, 18.5% have double glazing, and 57.4% double glazing

with reflective/absorbant thermal properties. Only one building has single glazing with re- flective/absorbant properties. However, there is not an evident correlation between the energy performance and the type of glazing.

2.5. Electrical demand The monthly average electrical demand is

47.7 W/m 2, with a standard deviation of 18.7 W/m 2, while the mode is 32.6 W/m 2, and the median is 43.7 W/m 2. The demand in offices built before 1970 is between 20 and 40 W/m 2, while for the new buildings the monthly average demand reaches 80 W/m2(Fig. 12). The pattern shown in Figs. 9 and 12 is un- doubtedly due to the larger use of electrical office equipment (e.g., typewriters, micro- and mini-computers, etc.), to the more extensive use of electrical energy for HVAC systems and to the increased number of large buildings requiring heating and cooling. The total elec- trical demand of the sample buildings was about 6 × 106 kW. In the case of all-electrical buildings the peak demand occurred in winter, while in the case of buildings using electricity and gas/ oil the peak demand occurred in summer. In both cases the probability of occurrence was about 70%.

2.5. Average cost 9f the equivalent kWh An indicator of the financial efficiency of

energy use is the average cost of the equivalent kWh, a high efficiency being obtained for a low cost. The average cost of the entire sample is 0.0408 S/kWh, with a standard deviation of 0.0136 S/kWh. The most frequent cost is 0.0375 S/kWh.

The offices built after 1970 perform at a relatively high cost above the average, reaching 0.06 S/kWh,which indicates a low financial efficiency, if compared with the older buildings, where the cost varies between 0.02 and 0.04 S/kWh (Fig. 13).

"r. 80 ". _~ ..

~ 80 ~ .--" ~ 40

• , :"

0 i I J i

1900 1920 1940 1960 1980 2 0 0 0

Year of cons t ruc t i on

Fig. 12. Ave rage m o n t h l y e lect r ical d e m a n d vs. yea r o f cons t ruc t ion .

69

0.08 i - ao6

._~ -~ 0.04

"S Q02 Q

° .

• °

..•.. • . . . . : :. . . :" --

I I J I

1900 1920 1940 1960 1980 Yeor of consfruction

2 0 0 0

Fig. 13. C o s t o f e q u i v a l e n t k W h vs . y e a r o f c o n s t r u c t i o n .

bJ _~_ ~ i i l s i l p i i o i * • weothef- dependen! energy

§

w • * i • •

I . . . . . I Tref

Averoge o u t d o o r t e m p e r o t u r e T o

Fig. 14. Building energy signature.

Iood

2. 7. E l e c t r i c i t y vs. o ther sources o f e n e r g y The total energy used by the sample buildings

in 1988 was about 970 x 106 kWh, at a total cost of 3 8 × 1065. The electrical energy had the major contribution to these totals, as it represented 68% of consumption and 73% of cost. The gas represented only 15% of con- sumption and 7% of cost, while the contribution of the oil was 15% of consumption and 6% of cost. The steam use was controlled by a flat rate contract, and as a result the con- sumption represented 2% of the total and the cost 14%.

3. Building energy s ignature

The analysis of data included in the utility bills provides additional information on the pattern of energy performance of the office buildings. For example, the dependency of heating or cooling consumption on the climatic conditions can be determined by plotting the daily average energy consumption versus the daily average outdoor temperature, and the corresponding relationship is called the "building energy signature" (Fig. 14). The daily average energy consumption is obtained by dividing the metered value, for a given period, expressed in equivalent kWh, by the corre- sponding number of days, and by the gross

rentable area. Then, the daily average energy use expressed in kWh/(m 2 day) is normalized for 16 hours of operation per day (see Section 1). The daily average outdoor temperature is calculated over the period of occupancy. The slope of the weather-dependent curve is given by factors such as conductive or convective heat loss rate, efficiency of HVAC systems or schedules for thermal control and operation. Zmeureanu [16] indicated, based on computer simulation, that the building energy signature does not change in time, unless some reno- vations, replacement of equipment or modi- fications in thermal control or operation have taken place.

Sharp and MacDonald [17] indicated there are two main methods used to define the linear correlation between the energy consumption of a building and the outdoor conditions, ex- pressed as outdoor temperature or heating degree-days:

(a) Maximization of the correlation coeffi- cient of the linear model, where all data of the total energy consumption are used. Hence, it takes into account both weather- and non- weather-dependent energy consumption. This method is used by the PRISM (Princeton Scorekeeping Method) model [18], which es- ¢imates the base-level consumption (non- weather-dependent) , the slope of the weather- dependent line and the reference or balance indoor temperature• Haberl et al. [ 19] applied an experimental version of heating-plus-cooling PRISM to an all-electric building, and obtained heating and cooling slopes, base-level con- sumption, and heating and cooling reference points.

Co) Separation of the total energy data into space-heating and base-level components. The regression analysis is applied only to the weather-dependent energy consumption. In this paper, this second method is used to analyze the utility bills.

By developing and analyzing the building energy signature, one can obtain useful in- formation such as non-weather-dependent en- ergy consumption (e.g., lighting, computers, escalators or cooling of internal zones) or slope of the weather-dependent curve, which indi- cates the efficiency of the HVAC systems and building envelope. This information completes the general pattern based on the annual data, and also gives a bet ter definition of the energy performance of each building.

70

The wea the r -dependen t energy signature is deve loped as a l inear function:

C = a + b T

where

C= daffy average energy consumpt ion (kWh/ (m e day))

T= daily average ou tdoor t empera tu re (°C)

a = i n t e r c e p t (kWh/ (m ~ day))

b = s l o p e of the wea the r -dependen t curve (kWh/ (m 2 day °C)).

Both coefficients a and b are calculated using the simple regress ion p rocedu re provided by the STATGRAPHICS package [20]. The ac- curacy of data fitting by the result ing l inear funct ion is tes ted using the corre la t ion coef- ficient R e and the t-statistic, p rovided also by the package.

The building energy s ignature deve loped un- der normal opera t ing condi t ions can be used by the building managers to evaluate some abnormal operat ions , and to define their causes. It can also be used to evaluate the net impact of the building retrofit , el iminating the effect of wea ther condit ions, by compar ing the nor- malized energy consumpt ion before and af ter improvements . This app roach is suitable for the Energy Monitoring and Control Systems, permit t ing a cont inuous evaluat ion of the opera t ing condit ions.

3.1. Bu i ld ings us ing gas and electrici ty The idea of developing a unique energy

s ignature of a building type (e.g., office build- ings, schools , houses or industrial plants) in a given locat ion seems very at tract ive. However , each building pe r fo rms differently, and as one can not ice in Fig. 15, it is not possible to define a unique heat ing energy s ignature for all office buildings in Montreal.

3

¢~- 2.5

~ 2 " I': " . . . . . • ~ , ~

= 0,5 '" ", " " " . " " _~m ° ° , o : ° ° ° °o , , , ~§ o , " : " ,

- I0 0 I0 20 30

Doily overage outdoor temperoture (°C)

Fig. 15. Daily average gas energy consumpt ion vs. daily average outdoor temperature for all sample buildings in Montreal.

The heat ing energy s ignature is obta ined for mos t buildings with a high corre la t ion coef- f ic ient ,between 0.7 and 0.985, which indicates high d ep en d en cy be tween the daily average gas use and the daily average ou tdoor tem- pera ture . For example , Fig. 16 shows the heat ing energy s ignature of an office building, with a corre la t ion coefficient R 2 = 0 . 9 8 , and t- statistic of 45.2 for in te rcep t a and 22.3 for s lope b. As the r an d o m variable t, ca lculated as follows,

la or bl t =

is g rea ter than the critical value t~. n-1 = 1.812 [21], then the t rue value of these coefficients (a or b) is significantly different f rom zero. The critical value is defined in t e rms of the level of significance c~ (that is, the probabil i ty to re ject the hypothes i s a=O or b = 0 when it is t rue) , and in this pape r the value of 0.05 was used. Therefore , one can say the energy s ignature of this building fits very well the consumpt ion data f rom the utility bills. The energy pe r fo rmance of this office with retail s tores, built in 1962 and using induct ion units loca ted in each ro o m (where the mixing be- tween the pr imary air and the rec i rcu la ted air is obtained) , is 693.1 kWh/(m2yr) and 17.9 $/ (m2yr).

The heat ing energy signature of this building can be wri t ten as follows:

G = 1 . 8 6 - 0.066TDB if TDB < 22 °C G = 0.4 if TDB > / 2 2 °C

where

G = d a i l y average gas energy consumpt ion (kWh/ (m 2 day))

TDB= dry-bulb ou tdoor t empera tu re (°C).

The average slope b of the heat ing weather- dependen t curve for the entire sample is 0.041

1.6 •

~ L2 o 9 0.8 ~ , E o~E

i .4 . ° . ~ o

-3 2 t2 22 32

Daily average outdoor temperature (°C)

Fig. 16. Energy signature of a gas-heated office building, with a correlation coefficient R 2 =0 .98 .

71

kWh/ (m 2 day °C), and varies be tween 0 .0091 and 0 .0776 kWh/ (m 2 day °C). The analysis of this s lope provides some in teres t ing obser- vat ions which conf i rm the prev ious conclu- sions. The offices built a f ter 1970 have a significant lower s lope of thei r hea t ing energy s ignature (Fig. 17), indicat ing a h igher effi- c iency of the HVAC systems, and be t t e r ex te r io r envelopes . As a ma t t e r of fact, mos t new build- ings have VAV systems, which are more energy- efficient than o the r sys tems such as cons tan t vo lume terminal rehea t or dual duc t sys tems, largely used in the previous period.

The degree of cor re la t ion be tween the daily electr ical energy consumpt ion and the daily average ou tdoo r t empe ra tu r e varies consider- ably among buildings. Both the dry-bulb and wet-bulb t e mpe ra tu r e s have been used in the statist ical analysis, and the resul ts did not show a significant difference. Therefore , in the fol- lowing analysis only the dry-bulb t empe ra tu r e is used. The coefficient R e takes values be tween 0.001 and 0 .9787 ,and is smaller than 0.5 for about 36% of buildings. Hence, in some build- ings the electr ical use is less affected by the climatic condit ions. Such a case is p r e sen t ed in Fig. 18, with no corre la t ion ( R 2 = 0 . 0 0 1 ) be tween the electr ical consumpt ion and the ou tdoor t empera tu re , the var ia t ion being cre-

Q08

~ o.o4~

~ " 0 o 3 u 1900

I I I 1920 1940 1960

Year of construction

°.

l

1980 DO0

Fig. 17. Slope of weather-dependent curve vs. year of construction.

0.47

~1 ~ 0.45 4

~= 0,59 12 5 ~ 2 6 ,~ - 0.55 7

~ o3~ F o ~ II0 9 8 = ~ 0.27 I i~

0 0.23 I I0 I I 13 2 ~2 22 32

Doily overage ouldoor temperature (*C)

Fig. 18. In this office building the use of electrical energy is not affected by the climatic conditions. The plotted number s indicate the mon th of year, from November 1987 (11) to November 1988 (118), pass ing through January 1988 (1) or June 1988 (6).

ated by o ther causes. This office wi thout a garage was built in 1910, and in Februa ry 1988 some renova t ions were under taken . The pe- r imete r zones use a cons tan t vo lume terminal r ehea t system, and the inter ior zones use in- duc t ion units. The electr ical energy use rep- resen ts 39% of the total ene rgy used, and the average electr ical demand is 26.5 W/m 2. The normal ized ene rgy consumpt ion is 311.7 k W h / (me]r) , and the normal ized cos t is 9 .43 $/(m 2 yr), indicat ing a be t t e r p e r fo rm an ce than the average of the ent i re sample, or even of its building type.

The energy s ignature of some o the r buildings can be drawn with a significant accuracy. For example , Fig. 19 shows the gas ( R 2 = 0 . 9 8 ) and electr ical (R 2= 0.97) ene rgy s ignatures of an office built in 1974 and using induct ion units. Fo r the gas ene rgy signature, the t- statistic is equal to 43.3 ( in tercept ) and 25.2 (s lope) , while the electr ical energy s ignature is equal to 6.8 ( in tercept ) and 9.6 (slope). The base electr ical load r ep resen t s abou t 35% of the total energy use, or 70% of the electr ical ene rgy use. The building requi res to be coo led when the o u td o o r t em p e ra tu r e ex ceed s 13 °C, and this is due to the high internal gains. The HVAC sys tem requi res s imul taneous cool ing (in central air handl ing unit) and heat ing (in induct ion units), which r educes the energy pe r fo rmance : 519.8 k W h / (m 2 yr) or 16.5 $/ (m 2 yr). The energy s ignature can be wri t ten as follows:

(a) Gas

G = 0 . 9 6 - 0.044TDB if TDB < 22 °C G=O if TDB>~22 °C

Co) Electr ic i ty

E=O.34+O.O22TDB if TDB> 13 °C E = 0 . 6 3 if TDB~< 13 °C

where E - - d a f f y average electr ical energy con- sumpt ion ( k w h / ( m 2 day)).

._o 0.75 ,, "....... ~ Elec,ricity

~ 0 . 2 5 ; . . . . 0 1 - I I I I

- 8 -5 2 7 12 17 22

Doily average outdoor temperature (°C)

Fig. 19. Energy signature of a building using gas and electricity, with a correlation coefficient R 2= 0.98.

72

One can not i ce f rom the w e a t h e r - d e p e n d e n t re lat ions that for a one -degree -Ce l s ius variat ion o f the daily average temperature , the gas energy use increases by 0 . 0 4 4 k W h / ( m 2 day), whi le the e lectrical energy use increases by 0 . 0 2 2 k W h / ( m 2 day). Therefore , this building is m o r e efficient in the coo l ing , rather than in the heat ing mode .

The electrical energy s ignature o f another bui lding is g iven in Fig. 20 (R e = 0 . 8 7 ) . This office w a s built in 1967 and has a l o w energy per formance: 852•5 k W h / ( m 2 yr) and 31 .7 $/ (m z yr).

The average s l ope b o f the e lectr ical weather- d e p e n d e n t curve for the entire sample is 0 . 0 1 6 k W h / ( m 2 day °C), and varies b e t w e e n 0 . 0 0 1 8 and 0 .037 .

3.2• All-electrical buildings As an example , the energy s ignatures o f two

al l-electrical bui ldings are p r e s e n t e d in Figs• 2 1 - 2 2 • The energy s ignature o f the first bui lding can be writ ten as fo l lows:

E = 1 . 1 4 8 - 0.0315TDB if TDB < 12 °C E = 0 . 7 7 if 12 °C~<TDB~< 15.5 °C E = 0 . 5 5 1 +0.0141TDB if TD~> 15.5 °C

One can not ice , again, that the s l ope o f the heat ing w e a t h e r - d e p e n d e n t curve is m o r e than

(xo.oI) $. 1 ,4

~, ~ ~o3.2

g ~ 92.4

8, - 2 8 81.6 _.__.~__

K

5 0

~= 7o8 k .//'/ ~ ._ . . . . . . . . u -'I ,--.

60 i J i - I0 0 I 0 20

Doily average outdoor t e m p e r a t u r e (°C)

Fig. 20. Electrical energy signature of a building using gas and electricity. When the outdoor temperature drops below O°C, some electrical preheating coils or baseboard heaters are turned on, in addition to the gas heating system.

(X 0.01)

~.~ ~ 9 ~ .

~ 7 7 "

-8 2 12 22 32 Dai ly o v e r a g e o u t d o o r t e m p e r a t u r e (*C)

Fig. 21. Energy signature of an all-electrical office building.

e ~

x g - a g o~

u

(XO01)

159 "~"~'~" 1 119 8~" "" 7~.

99 ~''''8 8 8 74.~'J'

79 7 "... 8 1 ~ . ~ ~ 7 7 1

3 9 7

- I I 2 9

I -I 9 19

Doily average outdoor t e m p e r a t u r e (°C}

Fig. 22. Energy signature of an all-electrical office building, showing an increase of the base load in July 1987.

8 O

60 " • :.

4O ~o • "

_ ~ ~ ~o .. • ,v

¢v I I I J o 1900 1920 1940 1960 1900 2000

Year of construct ion

Fig. 23. Base load-to-total electrical use ratio vs. year of construction.

6O

o ~ 40

8' ~, 2o ~, E

" ~ 0 0

1 • . . •

• . . . •

• - . . .

• o " . °

I I ]

20 40 60 80

Base l o a d / t o t a l e l e c t r i c a l use (%)

Fig.24. Average monthly electrical demand vs. base load- to-total electrical use ratio.

twice greater than the coo l ing one . Hence , this bui lding is m o r e sens i t ive to the co ld w e a t h e r condi t ions .

The s e c o n d Figure (Fig. 22) s h o w s an in- crease o f the base load o f about 0 .4 k W h / ( m 2 yr), w h i c h occurred in July 1987 , w h e n the d e m a n d increased f rom 97 .2 k W to 129 .6 kW. The lower curve c o r r e s p o n d s to the first s ix m o n t h s o f 1987 , and the upper curve to the nex t per iod until D e c e m b e r 1988 . The increase o f s l ope o f the heat ing and coo l ing curves can be exp la ined by a l ower eff ic iency o f the HVAC sys tem, w h i c h d o e s no t have e n o u g h capac i ty for the n e w condi t ions .

3.3. Non-weather-dependent energy consumption

The average n o n - w e a t h e r - d e p e n d e n t e lec- trical energy c o n s u m p t i o n (or base load) is 167 .6 k W h / ( m 2 yr), and varies b e t w e e n 45 and

360 k W h / ( m z yr). The mos t f requent value is 213 k W h / ( m z yr). In some offices built after 1970, the contr ibut ion of the base load to the total electrical c o n s u m p t i o n reaches 70% (Fig. 23), and consequen t ly the demand increased propor t ional ly (Fig. 24). Most buildings use electricity to heat the domest ic hot water, and in these cases the base load for gas or oil is equal to zero.

4. C o n c l u s i o n s

A large n u m b e r of data has been col lected during this survey, which allows different ob- ject ives to be establ ished in the analysis pro- cess. The results of the present path of analysis show two main conclusions:

(a) Al though the energy consumpt ion de- c reased in the last decade, there is still a large potential for improving the energy pe r fo rmance of office buildings in Montreal th rough bet ter design and operat ion. The average normal ized average consumpt ion is 502.2 k W h / ( m 2 yr), which exceeds by far the pe r fo rmance of the mos t efficient buildings, that is about 200 k W h / (m 2 yr). In te rms of energy cos t there is not a significant difference be tween old and new buildings.

(b) The office buildings built after 1970 show a very distinct pa t te rn of the energy perform- ance: (1) they are using less energy, expressed in equivalent k W h / ( m 2 yr); (2) electricity became the major source of energy because in the province of Quebec it is available at low cost (less than 0.05 S/kWh) and its supply is not affected by the geo-poli t ical crisis; (3) the cost of the equivalent kWh of the mos t recent buildings reaches 0.06 S/kWh; (4) they have more efficient HVAC sys tems and bet ter exter ior envelopes, as indicated by the lower s lope of the energy signatures.

The analysis p resen ted in this pape r was carr ied out on a macro-sca le using mainly informat ion f rom the utility bills. Therefore, the use of the daffy average energy consump- tion, obta ined by dividing the energy use for each interval by the co r re spond ing number of days, in t roduces some errors in analysis, if c o m p a r e d with the daily mete red values. These errors can alter the final conclus ions if applied to a detailed analysis of a par t icular building.

73

However, the objective of this paper is to define the overall pa t te rn of the energy pe r fo rmance of office buildings in a large city, Montreal, based only on the utility bills, which are usually accessible to the researchers .

Future work will include more detailed in- format ion related to the building opera t ion such as weekday versus weekend, base-level energy use ( compute r centres, equipment , lighting), quality of indoor envi ronment or pa ramete r s of HVAC systems. The addit ional informat ion will enable the au thors to define on a micro- scale the pa t te rn of energy use, and then to sugges t ways for reducing it.

A c k n o w l e d g e m e n t

The authors acknowledge the financial sup- por t of the National Research Council of Canada, Grant No. D-71.

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74

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