Development of an energy rating system for existing houses

Ž .Energy and Buildings 29 1999 107–119

Development of an energy rating system for existing houses

Radu Zmeureanu a,), Paul Fazio a, Sebastiano DePani b, Robert Calla b

a School for Building, Concordia UniÕersity, Montreal, PQ, Canada H3G 1M8b SIRICON, Montreal, PQ, Canada

Received 1 December 1997; accepted 3 June 1998

Abstract

This paper presents the development of a new energy rating system for existing houses, combining the information from utility billswith on-site measurements and computer simulation. The proposed system was tested on a sample of 45 houses in Montreal, with the

Ž . Žfollowing main objectives: i to evaluate the quality of results given by the system e.g., energy performance of houses, thermal. Ž . Žresistance of exterior envelope, air infiltration rate , and ii to evaluate the methods of measurement and simulation e.g., time required

.on site to collect data, time for computer simulation, accuracy of measurements and simulation . q 1999 Elsevier Science S.A. All rightsreserved.

Keywords: Residential buildings; Energy; Montreal; Measurement; Simulation

1. Introduction

First major step toward the improvement of energyperformance of an existing house consists in convincingthe owner of potential advantages such as the reduction ofutility bills due to energy savings, the increase in thermalcomfort or the increase of his property value. There arethree main approaches used for this purpose, which can beclassified, in terms of the main emphasis, as follows.

Ž .a The awareness approach, where the owner is in-formed about the actual performance of his house, com-pared with that of other houses such as an average house, ahouse built in the same year or a reference energy-efficienthouse. Sometimes a rating scale is used, similar to that of

Žthe quality of services offered by hotels e.g., a five-star.hotel compared with a two-star hotel . In addition to this

comparison of energy performance of a house, the poten-tial savings which can be obtained through renovations aresometimes presented to the owner.

Ž .b The financing approach, where the owner has accessto some advantageous financing schemes for investing inthe renovation.

Ž .c The quality of work approach, that is, the recogni-tion of professionals and their ability to provide high

) Corresponding author. Tel.: q1-514-8483200; Fax: q1-514-8487965

quality work. The builders associations are usually in-volved in the evaluation of potential savings, and guaran-tee the quality of work, including also the quality of indoorenvironment or the environmental friendliness.

The awareness approach can be very simple or verycomplex, and its development depends on the expectedlevel of accuracy, the time and cost constraints for per-forming the evaluation, and the final use of the assessed

Ženergy performance e.g., for comparison purposes only,for accurate estimates of energy savings, or for convincingthe financial institutions to invest in the energy-efficient

.renovation . Although this paper concerns only this ap-proach, it is recognized that the use of an optimum combi-nation of all three approaches is the key factor for asuccessful energy renovation program.

A detailed evaluation process is difficult to undertake,since a house is a complex system, where each sub-systemŽ .e.g., exterior walls, roof, windows, heating system con-tributes to the overall energy performance, and where thecross effects between sub-systems could play a major role.Different approaches have been developed in the past10–15 years to evaluate the energy performance of houses,using a simple index, and they are known under the

Ž .generic term of Home Energy Rating Systems HERS .These systems can be classified in the following three

Ž .main categories: 1 the points system, which evaluates theenergy performance of a house by giving points of perfor-mance or scores to each sub-system such as exterior walls,

Ž .roof or heating system; 2 the performance system, which

0378-7788r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved.Ž .PII: S0378-7788 98 00037-1

( )R. Zmeureanu et al.rEnergy and Buildings 29 1999 107–119108

assigns an index of performance in terms of the annualŽ .heating energy consumption or cost; and 3 the awareness

system, which recommends the annual total and heatingsite energy consumption, and the corresponding costs, interms of the year of construction of house, the climaticzone and the source of energy.

This paper presents the development of a new energyrating system, which combines the features of the perfor-

Ž .mance and awareness systems: i the index of energyperformance is assessed based on the previous history of

Ž .house, ii the results are compared with the energy perfor-Ž .mance of some reference houses, and iii the house’s

owner is informed about the potential energy savings,which can be obtained through the renovation or thechange of people’s habits. The proposed system was usedin a pilot project with 45 houses in Montreal, and theresults are presented in this paper.

2. Development of the proposed system

Most energy rating systems in place today were devel-oped for new houses, perhaps due to the easiness toevaluate the energy performance at the design stage, basedonly on drawings and specifications. So far about 96% ofenergy ratings in the United States were performed on the

w xnew houses 1 . This paper proposes a new energy ratingsystem for existing houses, which represent an importantmarket due to their large number and their potential forimprovement, when it is compared with that of new houses.For instance, between July 1993 and June 1994 about 45%of families in Quebec invested $4.4 billion to renovatetheir houses, but only in 3% of cases the initial reason forundertaking the renovations was the increase of energy

w xefficiency 2 . The proposed system could provide addi-tional incentives to houses’ owners to include in theirplans those renovations with an important impact on theenergy performance.

The development and application of this type of systemis much more difficult than one for new houses, since itmust take into account issues such as actual thermalperformance of exterior envelope or the occupants’ be-haviour, which is also affected by various socio-economi-cal factors.

2.1. Philosophy of the new system

The energy rating of a house is often compared with theŽ .index of gas utilization by cars e.g., 10 l for 100 km ,

which is normally measured under standard operating con-ditions in a laboratory. It is relatively easy to assess, at the

Ždesign stage, the standard conditions e.g., number ofoccupants, thermostat setting, use of domestic hot water,

.efficiency of heating system for the evaluation of theenergy performance of a new house. However, a ratingbased on the real performance of a given house, rather than

of a ‘standard’ house would add confidence for the buyeror owner. Since the lifestyle of the previous owner couldnot be relevant to the buyer, the system should evaluate, inaddition to the annual total energy consumption of house

Ž‘as-operated,’ the annual intrinsic energy consumption thatis, without energy utilization for domestic hot water, lights,

.appliances . Moreover, the difference between the totalenergy use and the intrinsic energy use is a good indicatorof the people’s maximum impact on the energy perfor-mance of house.

In the best case, the measurements performed in ahouse can only give an indication of the instantaneousenergy performance, and not the seasonal or annual perfor-mance. Therefore, the past energy performance is thekeystone in the development and application of the pro-posed energy rating system. Since, the only source ofinformation on the history of energy performance are theutility bills, their analysis constitutes a major step in theproposed system, where these data should be normalizedfor weather conditions and size of house to allow forcomparisons. The energy auditor can obtain from theutility bills both the energy consumption and the energycost. However, the impact on the client is more importantif the results are presented as dollars spent per year for theenergy used. It is more likely that the owner will becomecurious by the fact he spent about $400 per year more thanhis neighbour, who has a similar house, rather than 7700

Ž .kWh more all costs presented in this paper are in CAN$ .The rating scale can be developed using either an

absolute approach, where the actual energy performance ofeach house is compared with some fixed reference valuesŽ .e.g., an average new house or an energy-efficient house

Žor a relative approach e.g., comparing the actual housewith the same house built up to the level of an energy-effi-

.cient one . If the use of an index is an important elementfor influencing the house’s owner, then the absolute ap-proach allows for a unbiased comparison within the resi-dential stock. For instance, this approach will indicate the

Ž .house A built in 1990 belongs to the best 10% of allŽ .houses in Montreal, and the house B built in 1919 has an

energy performance which is lower than that of 75% of allhouses. In spite of major cost-effective renovations, thehouse B will never equal the quality of house A. If thepotential savings are the most important factor to bepromoted, then the relative comparison can show wherethere is an opportunity for investments. This approach will

Ž .indicate that house C built in 1947 could improve theenergy performance by about 45% to reach its maximumpotential, while the corresponding increase for house DŽ .built in 1987 is about 15%. The absolute approach waspreferred in the development of the proposed system, sinceit promotes the actual quality of houses, and then willenable some houses to become the champions of themarket.

The rating process should be designed in such a way tobe cost-effective for both the house’s owner and the

( )R. Zmeureanu et al.rEnergy and Buildings 29 1999 107–119 109

auditor, less disturbing for the house’s owner, and toprovide results of a reasonable accuracy for the purposeswhich are sought.

2.2. Summary of the proposed system

The proposed energy rating system has the followingsteps.

Ž .1 Analysis of utility bills using the AHEM software,for a fast and inexpensive evaluation of energy perfor-mance. It performs the weather normalization, and calcu-

Ž .lates the Normalized Annual Energy Consumption NACŽ .and Cost NACo as well as other indices. The results are

compared with similar data from some reference houses.The major role of this step is to inform the client and thento raise his interest for a more detailed evaluation. A faircomparison between the energy performance of a givenhouse, based on the analysis of utility bills, with somereference houses can be done only if the general operating

Ž .conditions are similar. For example, the house must iŽprovide a comfortable indoor environment thermal, visual,

. Ž .acoustic, indoor air quality , and ii be used as a principalresidence over the most part of year. In other cases, suchas a house underheated due to the occupants inability topay the bills, or all occupants spending the winter seasonunder warmer skies, these particular conditions should beindicated along with the results of analysis.

Ž .2 Assignment of an index of energy performance inŽ .terms of Normalized Annual Energy Cost NACo , which

can give a first idea about the potential savings. Forinstance, if the house has an index equal to or better thanan average new house, then the potential savings areconsidered to be negligible. If the client wishes no furtherauditing of his house, the energy rating process stops here.If not, then steps 3 to 7 are performed.

Ž .3 The infrared camera is used to identify, in a qualita-tive way only, the thermal bridges and the voids in theexterior envelope, and to show them to the house’s owner.Some representative locations are then selected and themeasurement of thermal resistance of exterior envelope isperformed. The air infiltration rate at 50 Pa is measured byconducting a blower door test.

Ž .4 Collection of other data such as the size of exteriorwalls and windows, the indoor temperature or the type andcapacity of heating system, which are required by thecomputer simulation of the actual house, using theHOT2000 software.

Ž .5 Development of a computer model of the actualhouse by using the HOT2000 program, and its calibrationwith the utility bills. The HOT2000 program is only used

Ž .for i the evaluation of potential energy savings due to theŽ .house’s renovation, and ii the evaluation of intrinsic

energy usage.Ž .6 Selection of the most appropriate energy conserva-

tion measures and the estimation of the potential energy

savings by computer simulation. Estimation of initial costsrelative to these renovations.

Ž .7 Submission of a summary report to the house’sowner.

2.3. Analysis of utility bills

Steps 1 and 2 of the proposed system are presented indetail in this section, while the others are presented inSection 2.4, along with results from the pilot project with45 houses.

The AHEM software was developed based on studiesw x w xcarried out by Zmeureanu 3 , Zmeureanu and Zhaonan 4

w xand Zhaonan 5 . The input file contains the followingdata.

Ž .a Year of construction. This information is required tocompare the energy performance of the house under analy-sis with that of houses built in the same period, which isobtained from a database integrated within the AHEMsoftware.

Ž .b Total heated floor area. This information is requiredto normalize the annual energy performance.

Ž .c Location of house. This information is used by thesoftware to select the appropriate weather data file, whichcontains the daily mean outdoor temperature from 1973 till

Ž1996. Presently, weather data for two cities Montreal and.Quebec City are available.

Ž . Ž . Ž .d Type of energy source used for i heating and iidomestic hot water: electricity or oilrnatural gas.

Ž .e Energy consumption and cost for each billing pe-riod, for all energy sources, covering at least the last 12months. The accuracy of developing the house energysignature increases with the number of billing data.

Ž .The following main results are obtained: a Actualenergy consumption and cost for each energy source andbilling period, as well as for the whole year, expressed as$rm2 day, $rm2, kWhrm2 day, kWhrm2 and $rkWh.

Ž .b Normalized annual energy consumption and cost.The weather-normalization technique is based on the as-sumption that the energy consumption in a house is com-

Žposed of a non-weather-dependent component e.g., for.lighting, appliances, domestic hot water which is almost

constant throughout the year, and a weather-dependentcomponent, which varies linearly with the outdoor temper-ature. First, the energy signature of the house is estimatedby assuming a simple linear regression between the daily

Ž .average energy performance consumption and cost andthe corresponding daily average outdoor temperature:

w 2 xEnergysaqbPT kWhrm dayo2w xCostscqdPT $rm dayo

The energy signature does not change in time, unlesssome renovations or modifications in operation take placein the house. Therefore the billing data before the lastmajor renovation cannot be used. Second, the normalizedannual energy consumption and cost are evaluated for anaverage year, by using the energy signatures and the


frequency of occurrence of several temperature bins, usingdaily outdoor temperatures recorded by EnvironmentCanada at the Dorval airport between 1973 and 1995.

The annual normalized energy consumption is brokenŽ .down in two components: i the non-weather-dependent

Ž . Ž .energy use e.g., domestic hot water, lighting , and ii theweather-dependent energy use, that is, for heating andcooling. Additional disaggregation of these two compo-nents based only on the utility bills, and without somehistorical relevant information about the usage pattern,cannot be accurately done.

The normalized energy consumption represents the siteenergy use, while the normalized energy cost includes thecost of production, transport, distribution and service of-fered by the utility company.

Ž .c Contribution of each energy source to the normal-Žized annual energy performance e.g., electricity accounts

for 45% of the energy consumption, but for 55% of the.energy cost .

Ž .d Comparison between the normalized annual energyŽ .performance consumption and cost and some reference

Ž .values, which are developed for: i an average house builtin the same period; this information is obtained from a

Ž .database coupled with the software; ii a R-2000 house,Ž .which is an energy efficient house built in Canada; iii an

Advanced House, which is an experimental house devel-oped in Canada by using the available technologies inorder to reduce by half the energy consumption of aR-2000 house; the measurements of such houses indicatedan annual energy consumption of 47 kWhrm2 yearŽ . 2 Ž .Novtec house in Montreal , 50 kWhrm year Waterloo ,

2 Ž .and 69 kWhrm year Ottawa .The energy performance of a R-2000 house is evalu-

w xated, using the 1992 version of R-2000 target 6 . Thistarget was changed in September 1994. However, thestudy presented in this paper was initiated before thechange took place. The relationships used for assessing the

w xR-2000 target are the following 6 :w 2 xEnergy consumption for heating kWhrm year

Ž .ECHsSP 5q55PHDDr6000w 2Energy consumption for domestic hot water kWhrm

xyearEDHWs4745PBrHeated floor area

Energy consumption for lighting and appliancesw 2 xkWhrm year

ECLAs6534rHeated floor areaw 2 xEnergy cost for heating $rm year

Ž .ECoHsECHP$r equivalent-kWh for heating averagew 2 xEnergy cost for domestic hot water $rm year

ŽECoDHW s EDHW P equivalent-kWh for lighting.and appliances average

w 2 xEnergy cost for lighting and appliances $rm yearŽECoLAsECLAP equivalent-kWh for lighting and

.appliances average

Energy consumption of a R-2000 housesECHqw 2 xEDHWqECLA kWhrm year

Energy cost of a R-2000 housesECoHqECoDHWqw 2 xEcoLA $rm year .

Where Ss1.00 kWh for electric heating, and 1.25 kWhŽ .for oil or natural gas; HDD Heating Degree-Days s4550

for Montreal, and 5165 for Quebec City; Bs1.075 kWhfor an electric domestic hot water tank, and 2.00 kWh for atank using natural gas or oil.

2.4. Indices of energy performance

Since the existing rating systems use either a numericalindex or a ‘star’ index, at this stage the proposed systemuses both types. A market study could show later whichtype of index is more effective for influencing the ownersor convincing the financial institutions to support theenergy renovations. The first type of rating scale was

Ž .developed by imposing the following two constraints: athe index should tend to zero when the normalized annual

w 2 x Ž .energy cost $rm year is too large. b The index shouldtend to 100 when there is no need to purchase energy for

Žsatisfying the occupants needs e.g., heating, cooling, do-.mestic hot water . Moreover, the house could become a

producer of energy by using the renewable sources such assun or wind, or by recovering heat from the internalsources.

The rating scale has an asymptotic variation when theindex approaches the two extremes, that is when the houseis either very energy-efficient or energy inefficient. Forthese two extreme cases, the index of energy performancecan be improved only if some large and expensive renova-tions are undertaken. The following continuous unipolarfunction is proposed to express the index of energy perfor-

Fig. 1. Relationship between the index of energy performance and thenormalized annual energy cost.


Fig. 2. Comparison between the proposed rating scale and other scales in use.

Ž .mance IND in terms of normalized annual energy costŽ .NACo :

100INDs100y

1qexp ylP NACoyaŽ .where a is the normalized annual energy cost of anaverage house built in Quebec after 1985, that is comply-ing with the present standard of energy efficiency in

w xbuildings 7 . This average energy cost was evaluated to beabout 9.00 $rm2 year, based on a survey of 115 housesw x8 . Since this reference house is assumed to have anaverage energy performance, it has an index of 50 on a0–100 scale. The second coefficient, l, is calculated to beequal to 0.275 by assuming the annual energy cost of theR-2000 energy-efficient house is about 5.00 $rm2 year.Although it is recognized today as an energy-efficienthouse, it does not have the maximum performance. Hence,it has an index of only 75 out of 100. Fig. 1 shows the

Table 1Sample of houses used in the present study

Year of Percentage of Heated floor areaŽconstruction total number of average"standard

2w x .houses % deviation, in m

Before 1921 5 212"161921–1945 10 174"551946–1960 12 211"871961–1970 12 212"81971–1980 23 253"1211981–1985 10 199"431986–1990 21 282"99After 1990 7 266"84

relationship between the index of energy performance andthe normalized annual energy cost. The annual energy costof these two reference houses must be updated periodicallyto take into account the variation of energy cost for allsources as well as the increase of energy efficiency of newhomes. 1

A second type of index assigns stars of performance inw 2 xterms of the normalized annual energy cost $rm year .

The approach used in developing this index is presentedbelow.

Ž .a If the annual energy cost is between 85% and 115%of that of an average new house, that is between 7.65 and10.35 $rm2 year, the house is considered to have an

Ž .average energy quality and receives a two-star index )) .Assuming the annual energy cost of houses follows anormal distribution around the average value of 9.00 $rm2

1 One reviewer of this paper presented an interesting potential argu-ment against the rating system based on energy cost. In his opinion, the

Ždistortions in the energy price e.g., price increases imposed politically,dynamics of the international energy supply, exclusion of environmental

.costs could affect the duration of validity of a rating given to a house.Under theses conditions, he would prefer a rating system based on energyconsumption, which is insensitive to these changes. In our opinion, thefinal indicator of the energy performance in a free market should be thedollar sign, in spite of several economical and political phenomena whichcould modify the energy price from day to day or month to month. Inorder to accommodate the variation of energy price, the relationshipbetween the index of energy performance and the annual energy costmust be updated periodically. For instance, a correction factor equal to1.0 should be used for the energy price at the time of implementation ofthe proposed system, and then its value should be periodically updated in

Žterms of increaserdecrease of energy price e.g., a weighted average.price of major sources .


Table 2Percentage of total number of houses. Comparison between the sample

´ w xused in the present study and the Eval-Iso study 10

´Year of construction Present study Eval-Iso study

Before 1946 15% 10%1946–1970 24% 25%1971–1985 33% 44%After 1986 28% 21%

year, the probability of receiving a two-star index is equalw xto 0.3182 9 .

Ž .b The probability of finding some houses with ahigher energy performance is only half of that of anaverage house, that is equal to 0.1591. This new probabil-ity along with the performance of a R-2000 house allowsfor defining the boundaries of the following categories:

Ž .-a three-star house ))) or R-2000 class, with anannual energy cost between 5.00 and 7.65 $rm2 year;

Ž q. q-a three-star plus house ))) or R-2000 class, withan annual energy cost between 2.40 and 5.00 $rm2

year;Ž .-a four-star house )))) or an advanced house, with

an annual energy cost between 0 and 2.40 $rm2 year.Ž .c The probability of finding some houses with a lower

energy performance is equal to that of an average house,that is equal to 0.3182. This probability allows to define

Ž .the lower boundary of one-star house ) or a house with aperformance lower than the average. The annual energycost is between 10.35 and 15.6 $rm2 year.

Ž .d All houses with the annual energy cost greater than15.6 $rm2 year are called very inefficient houses, and donot receive any star of performance.

For instance, if the annual energy cost is equal to 14.5$rm2 year, the house has an index of 20 out of 100 andreceives one star of performance. To improve its index,from one to two stars, the annual energy cost must bereduced to 10.35 $rm2 year, or by about 29%.

Fig. 2 shows a relative comparison between the pro-posed rating scale and some other scales in use: Home

Ž .Energy Rating System HERS USA , Energy Rated HomesŽ . Ž .of America ERHA USA and Star Point UK . These

systems use different approaches to assess the index of

Fig. 3. Distribution of number of houses vs. index of energy performance.

performance, and therefor their comparison should con-sider these differences. This figure is included in the paperonly to show the relative weight given by each system toadjectives such as ‘acceptable, good, average, efficient orexcellent’, which are used to qualify the energy perfor-mance of house.

3. Results from the use of proposed system

The proposed system was tested on a sample of 45Ž .houses in Montreal Table 1 , between January and March

Ž .1995, with the following main objectives: i to evaluateŽthe quality of results given by the system e.g., energy

performance of houses, thermal resistance of exterior enve-. Ž .lope, air infiltration rate , and ii to evaluate the methods

Žof measurement and simulation e.g., time required on siteto collect data, time for computer simulation, accuracy of

.measurements and simulation . Some results of this studyare presented in terms of the year of construction of houseto suggest some trends and eventually recommendationsfor future work. A comparison between these results and

´ w xthose given by the ‘Eval-Iso’ study 10 , carried out be-tween 1992 and 1994 using a sample of more than 1000

Table 3Ž .Normalized annual energy performance of the present sample average"standard deviation

Year of Energy consumption Energy cost Index of performance2 2w x w x Ž .construction kWhrm year $rm year out of 100

Before 1921 202.6"0.5 8.8"0.2 52"11921–1945 260.8"120.2 12.8"4.1 30"181946–1960 180.9"60.9 10.0"2.1 44"141961–1970 167.6"41.5 8.3"1.0 55"71971–1980 177.3"33.4 10.1"1.6 43"101981–1985 145.3"42 8.7"1.5 52"101986–1990 123.8"29 8.0"1.8 56"12After 1990 107.6"1.6 7.0"0.1 63"1


Table 4Ž 2 .Thermal resistance average"standard deviation, in m 8CrW of the exterior envelope of present sample, evaluated by three methods

Year of construction Above-grade walls Ceiling

M1 M2 M3 M1 M2 M3

Before 1921 0.7"0.1 1.9"1.7 1.9"0.5 7.8"6.7 3.0"1.7 3.0"1.71921–1945 3.6"3.5 2.1"0.9 1.5"0.3 2.3"0.8 3.7"2.5 4.4"3.81946–1960 1.2"0.9 3.9"3.0 2.3"1.2 1.6"0.5 5.3"3.9 2.7"1.01961–1970 3.1"2.0 3.0"2.4 2.2"0.7 3.9"2.6 7.5"4.1 6.0"1.71971–1980 2.1"0.4 2.8"1.1 2.9"0.5 3.5"1.5 5.3"3.2 4.9"0.81981–1985 4.5"2.0 2.3"0.8 3.5"0.3 9.4"3.8 6.6"2.5 5.9"1.01986–1990 2.1"0.7 3.2"2.4 3.7"0.4 3.1"1.6 8.7"4.8 6.1"0.9After 1990 4.1"3.1 5.0"3.5 4.0"0.3 6.3"4.3 7.8"4.6 5.6"0.5

Ž .houses single family, duplex and triplex , is also pre-Ž .sented Table 2 .

3.1. EÕaluation of energy performance of houses

Table 3 presents the normalized annual energy perfor-mance of the sample houses in terms of the year ofconstruction, based on the analysis of utility bills coveringin most cases 12–14 months and a full heating season. Thecorresponding average index of performance, calculated interms of annual energy cost, is also presented. As ex-pected, the houses built more recently have a higher indexof energy performance than the majority of older ones. Forinstance, the houses built after 1981, which comply with

w xthe present standard 7 , receive more than 50 points out of100, while houses built between 1921 and 1945 have anaverage index of performance of about 30r100. The pre-sent standard regulates the construction of new houses inQuebec, to achieve a minimum level of energy perfor-mance by using those measures which are cost effective.The standard is based on a prescriptive approach andrequires minimum levels of thermal insulation for different

Ž .sub-systems e.g., walls, windows, roof or minimum effi-ciency for heating system.

The energy performance of houses follows a normalŽ .distribution Fig. 3 : 60% of houses receive two stars or

between 40 and 59 out of 100, 17% receive one star orbetween 15 and 39, and 19% receive three stars or between60 and 74, which is equivalent to a R-2000 house. Onehouse receives three starsq, since it has a high energyperformance of 80r100.

3.2. EÕaluation of thermal resistance of exterior walls andceiling

The following three different methods of evaluationwere used in this study, to verify their usefulness andcost-effectiveness; finally, the third method was proposedto be used in the rating system.

Ž .1 The thermal resistance was evaluated in terms of theheat flow through the element, measured with heat fluxsensors, and the temperature difference between the insideand outside surface of the same element, measured withthermocouples. A data acquisition system was used torecord this information, over a period of about 2 h.

Ž .2 The measurements of heat flow and temperatureswere performed using a portable infrared pyrometer, andthen the thermal resistance was evaluated in a similar wayas in the first method.

Ž .3 The type and thickness of layers in the exteriorwalls and ceiling were defined by a visual inspection, andthen the corresponding thermal conductivities were se-lected from textbooks to calculate the thermal resistance ofthe entire element. The same method was already used in

´ w xthe Eval-Iso project 10 .The three methods gave the same expected pattern

Ž .Table 4 : the most recent houses have a higher insulationlevel than the old ones. However, the statistical ‘t-test’,with a level of significance equal to 0.05, indicated thedifference between results is statistically significant. The

Ž .results given by method 1 are affected by i the intensityŽ .of heat flow measured on the inside surface, ii the

Ž .location of heat flux sensors, iii the temperature differ-

Table 52 ´w x w xAverage thermal resistance of exterior envelope m 8CrW . Comparison between the present study and the ‘Eval-Iso’ study 10

´Year of construction Present study Eval-Iso study

Above-grade walls Ceiling Above-grade walls Ceiling

Before 1946 1.61 3.93 2.56 3.461946–1970 2.21 4.34 2.46 4.331971–1985 3.20 5.38 3.03 4.80After 1986 3.73 5.95 3.64 5.45


Ž .ence between the inside and outside surfaces, and iv thew xduration of measurements. ASTM Standard C 1155-90 11

recommends the test should last one or more multiples of24 h. However, a duration of this length will make therating process uncomfortable for the house’s owner, andalso will increase the rating cost since the team must makean additional visit for collecting the equipment with themonitored data. The results given by method 2 are affectedby the continuous calibration which is required by theinfrared pyrometer, as well as by the intensity of the heatflow and the temperature difference between the inside andoutside surface. Both methods become less accurate if theoutdoor temperature increases, which limits their applica-

Žtion only to a few months e.g., from December till.March . During the heating season there are also some

mild days, when the temperature difference between theoutside and inside of the house is much lower than therequired value. Since the method 3 is not affected by thistype of problem and can easily be used by field auditors,its results are further used in this paper to develop thecomputer model of each house, and to estimate the poten-tial for energy savings. Table 5 shows a comparisonbetween the results given by method 3 and those from the´‘Eval-Iso’ study.

3.3. EÕaluation of air infiltration rate

The measurements were performed according to aw xCanadian standard 12 , and the average air infiltration rate

in terms of the year of construction is presented in Table 6.The measurements follow the expected pattern: on theaverage the new houses are tighter than the old ones. Thecomparison between the present results and those from the´‘Eval-Iso’ study are presented in Table 7. The use of

blower door measurements has an important impact on theaccuracy of results, and has also a great ‘market’ value,since most owners were very impressed by the conclusionsderived from measurements.

3.4. DeÕelopment of computer models using the HOT2000program

HOT2000 software was developed for the evaluation ofenergy performance of houses, based on algorithms from

Table 6Ž .Air infiltration rate average"standard deviation, in ach measured at 50

Pa pressure difference

w xYear of construction Air infiltration rate ach

Before 1921 7.3"0.31921–1945 7.7"1.81946–1960 7.5"1.81961–1970 6.7"1.11971–1980 6.8"2.01981–1985 5.2"1.11986–1990 5.0"1.4After 1990 3.9"1.0

Table 7Average air infiltration rate. Comparison between the present study and

´ w xthe ‘Eval-Iso’ study 10

´ w xYear of construction Present study Eval-Iso study 10

Before 1946 7.6 9.281946–1970 7.1 6.061971–1985 6.3 4.68After 1986 5.5 4.17

the National Research Council of Canada, and was contin-uously improved from its first version called HOTCAN,and periodically validated with field data or by comparison

w xwith other programs such as BLAST or DOE2 13–18 .The program was also submitted to the full BESTESTvalidation procedure, developed by the International En-ergy Agency, and showed excellent agreement with other

w xnine hourly simulation reference programs 19 . Presently,another version called AUDIT2000 is available for theenergy audit of houses.

The quality of results from the computer simulationdepends on several factors: the user’s experience, thequality of input data concerning the building envelope andthe heating system, the occupants’ behaviour, the weatherdata file, and the algorithms of HOT2000 program. Whenthe reference is made in this paper to the simulationresults, all of the above factors are considered.

The computer model of each house was calibrated withthe utility bills, by imposing the maximum differencebetween the simulation results and the measured data, onthe annual basis, to be less than 20%. Some factors, withhigh uncertainty in evaluating the as-built or as-operatedconditions, were selected and then their value modifiedwithin a reasonable range, in order to achieve the target of20%. Such factors are: thermostat setting, temperature ofbasement, daily average use of domestic hot water,steady-state efficiency of heatingrair-conditioning system,heat losses from the domestic hot water tank, daily averageelectricity use for appliances and lights. The average dif-

Fig. 4. Ratio between the thermal resistance of exterior walls of thesample houses and that of a R-2000 house.


Fig. 5. Ratio between the thermal resistance of ceiling of the samplehouses and that of a R-2000 house.

ference for the entire sample was 16.1%; 14.9% for all-Ž .electric houses 69% of the sample , 17.2% for thoseŽ .heated with oil 21% of the sample , and 22.6% for thoseŽ .using natural gas 10% of the sample . Although within the

accepted limits, in 76% of cases the simulation resultsoverestimated the actual energy consumption. Only for 8

Ž .houses 18% of the entire sample it was not possible, byusing reasonable assumptions, to calibrate the model within20% difference. For those cases, some large differences of25 to 40% were obtained, mainly due to the following

Ž .factors: i unreliable information obtained from the house’sowner regarding the base load consumption and the ther-

Ž .mostat setting, and ii lack of access to the roof toevaluate the thermal resistance of ceiling.

3.5. EÕaluation of potential energy saÕings

The paper presents the maximum potential energy sav-ings which could be obtained by renovating each house up

Ž .to the level of: i a house built in compliance with theminimum cost-effective prescriptions of the energy stan-

w x Ž .dard in Quebec 7 , and ii an energy efficient R-2000Žhouse, which should meet the performance target as pre-

.sented in the previous section . However, the actual sav-

Fig. 6. Ration between the air infiltration rate of sample houses and thatof a R-2000 house.

Fig. 7. Maximum impact of people’s behavior of the annual energy cost.

ings could represent only a portion of the maximumpotential savings, since the renovation costs could limit theextend of measures, in order to keep them as cost-effec-tive. The renovation costs were not considered in thisanalysis for the following reason: if the proposed systemwill be implemented, the cost of renovations are expectedeither to increase or decrease, depending on the marketdynamics; therefore, some renovations accepted today, willnot be more cost-effective tomorrow.

The ratio between the thermal resistance of exteriorenvelope and the minimum value required for an energy-efficient R-2000 house shows the potential energy savings

Ž .with respect to the new houses Figs. 4 and 5 . Forinstance, houses built before 1970 have an average thermalresistance of the exterior walls of only 40 to 60% of therequired minimum value.

The air infiltration rate of houses built before 1981,measured at 50 Pa pressure difference, is about four to fivetimes greater than the required value for a R-2000 houseŽ .1.5 ach , which indicates an important potential for en-

Ž .ergy savings Fig. 6 . However, this potential cannot bealways reached, since when a house is renovated to thelevel of R-2000 and becomes tighter, the installation of amechanical ventilation system becomes compulsory. In

Fig. 8. Ratio between the annual expected energy savings and thenormalized annual energy cost.


Fig. 9. Distribution of number of houses vs. annual expected energysavings.

this case, some additional energy is needed for the circulat-ing fans and for heating the outside cold air brought intothe house. Although a heat recovery ventilator can beinstalled, the energy consumption can increase after thistype of renovation. It should also be noted that the qualityof indoor air is expected to improve, since the mechanicalventilation system will bring a constant rate of outside airinto the house.

The intrinsic energy consumption due to the exteriorenvelope was evaluated by modifying the computer modelof each house in such a way to eliminate completely theenergy usage due to the occupants such as lighting, domes-tic hot water or appliances. The difference between thetotal energy consumption and the intrinsic energy con-sumption gives an indication of the maximum impact thatthe people’s behavior can have on the energy performanceof the house. These results led to the opinion that, by

changing the people’s habits, the annual energy cost couldŽbe reduced on the average by a significant amount for

instance, about $450ryear for houses built between 1981–. Ž .1985 Fig. 7 . However, the actual savings are expected to

be less than the maximum potential, and they depend onfactors such as the number, age and activity of occupants,their life style, or the type and number of home appliances.

The ratio between the annual expected energy savingsŽ .and the normalized annual energy cost Fig. 8 indicates

w xthe improvement up to the level of present standard 7 canreduce the utility bills of houses built before 1971 by 15 to25%, while the renovation up to the level of R-2000 housegives reductions of 25 to 35%. For those houses built after1971, it appears to be more cost-effective to influence thepeople’s behavior. For instance, for an average house builtin 1983, the expected savings due to the improvement upto the present standard are about 10%, while the modifica-tion of people’s behaviour can have a maximum impact ofabout 25%. Another study quantified the potential energysavings produced by changes in people’s lifestyle in the

w xresidential sector and found them quite substantial 20 :15–40% for domestic hot water, 35–60% for lighting,0–60% for refrigeration, 15–60% for cooking and 5–55%for appliances.

The renovations up to the level of present standard areexpected to generate average energy savings of less than

Ž .$500 per year, for about 88% of houses Fig. 9 . Theimprovement up to the level of R-2000 house can producesavings ranging from $100ryear and more than $700ryear.

3.6. Summary report to the house’s owner

The report contains information about the actual energyperformance of house, and the estimation of potential

Table 8Time used by a team of two persons

Task Average value Standard deviationw x w xmin min

Use of infrared camera 50 20Visual inspection, outside and inside the house 54 25

aEvaluation of thermal resistance, method 1 185 28Evaluation of thermal resistance, method 2 25 11Evaluation of thermal resistance, method 3 70 31Measurement of air infiltration rate with a blower door, and use of smoke pencils 67 25to detect the air leaksEvaluation of annual normalized energy performance using the AHEM software 34 22Development of a computer model using the HOT2000 software 195 83

bEstimation of potential energy savings 27 3cOral explanations to the house’s owner 23 16

Transport and installation of equipment 23 8Photos of outside and inside the house 8 8Evaluation of burner efficiency 24 9

a Ž .It includes the time for recording the heat flux and the temperature difference between the inside and outside surfaces about 120 min ; the team needsabout 65 min.b This task was realized in the office.c The oral presentation includes the objectives of the study, the interpretation of measurements, the conclusions from the analysis of utility bills, theproblems noticed during the inspection, and the recommended renovations.


Ž .energy savings: a normalized annual energy performanceŽ . 2each energy source, and total , expressed in $, $rm ,

2 Ž .kWh, kWhrm ; b intrinsic normalized annual energyŽ .performance, which was evaluated for an empty house; c

maximum potential impact of occupants on the annualŽ .energy performance; d comparison between the normal-

ized annual energy performance of the house and that ofan average house built in the same period, and also with a

Ž .R-2000 house; e thermal resistance of exterior envelopeŽ .walls, roof, windows and the air infiltration rate at 50 Pa;comparison with the corresponding values of an averagehouse built in the same period, with a house built inaccordance with the present standard, and also with a

Ž .R-2000 house; f disaggregation of total energy consump-Žtion among the major end-uses: heating infiltration and.ventilation, walls, doors and windows, roof , domestic hot

Ž .water, and lighting and appliances; g potential impact ofŽ .renovations to update the quality of house 1 to the level

Ž .of present standard, and 2 to the level of R-2000 houseŽ .energy savings in $ryear, initial cost .

3.7. Analysis of time required for each task

The on-site team was composed of a junior engineerand an undergraduate engineering student, without a priorexperience in performing the required tasks. The averageduration of a complete evaluation was 12.6"2.5 h, whenthe transport is not considered, and 14.2"2.4 h, when thetransport is included. The duration of each major task ispresented in Table 8.

4. Discussion

Since the duration of some tasks did not diminishduring the field experiment, it is impossible to speak about

a learning curve. However, after the project was completedand all aspects were discussed, the team re-evaluated thetime required at 3.8–4.2 h on-site and 1.3 h in the office,

Ž .for a total of 5.2–5.5 h Table 9 . The cost of home ratingis evaluated at $533 to $568, assuming an hourly rate of$58 for an junior engineer and $45 for a technician. Thecost of equipment and transportation is not included.

Without changing the concept of proposed rating sys-tem, further reduction in time could eventually be ob-

Ž .tained; some suggestions are the following: i the scan-ning of utility bills and the automatic integration of results

Ž .of their analysis in the owner’s report; ii the use ofdefault files for typical houses, which have been developedfor the AUDIT2000 program, in order to lead the energyauditor through the main menus; the fields correspondingto variables which must be measured or evaluated on-sitemust be left empty, to avoid the tentation of using default

Ž .values; iii the direct transfer of data collected on-site,between the electronic pad and the AUDIT2000 program;Ž .iv the development of a methodology for automaticcalibration of the computer model with the utility bills; theenergy auditor should select those parameters consideredto have a high uncertainty in assessing their values and thepossible limits of variation; the program should then per-form the parametric simulations for all those parameters,and finally to recommend the combination with the bestfitting to the utility bills.

ŽHowever, only the market forces e.g., owners, banks,.buyers will finally control the cost, the duration and the

needed accuracy of the evaluation process.There are some trends, noticed in other energy labelling

Žsystems, toward the use of some defaults values e.g.,thermal resistance of exterior envelope, air infiltration rate,

.efficiency of heating system , in order to reduce the timeand cost required by the auditing process. If this approach

Table 9Suggested time for a team of two persons

w x Ž .Tasks Average time min Cost $

I. Tasks on siteUse of infrared camera 30 52Visual inspection, outside and inside the house 30 52Evaluation of thermal resistance, method 3 60 103Measurement of air infiltration rate with a blower door, and use of smoke pencils to 20 34detect the air leaksEvaluation of burner efficiency 20 34Evaluation of annual normalized energy performance using the AHEM software 30 52Data collection for the development of computer model using the HOT2000 software 40 69Transport and installation of equipment 20 34

a b a bTotal I 230 –250 395 –430

II. Tasks in the officeDevelopment of the computer model using the HOT2000 software 80 138Estimation of potential energy savingsReport for the house’s owner

a b a bTotal Iq II 310 –330 533 –568

a The evaluation of burner efficiency is not included.b The evaluation of burner efficiency is included.


Table 10w xEstimated annual energy savings $

Year of Source of Above-grade Ceiling Basement Air infiltration Totalconstruction data walls walls rate

Before 1921 Monit 73 73 13 32 125Default 23 53 2 13 74

1921–1945 Monit 329 – 53 147 529Default 48 – 10 67 264

1946–1960 Monit 210 155 133 172 670Default 37 24 31 207 297

1961–1970 Monit 63 – – 29 92Default 84 – – 34 174

1971–1980 Monit 67 31 – 71 179Default 37 16 – 145 296

is used with the proposed system, and the default valuesare developed by using the ‘Eval-Iso’ study, the timeneeded for in-situ measurements could be reduced by 80 to100 min. However, in this case the computer model isexpected to be more representative of an average house, asdefined by the default values, than of the real house underanalysis. What is the impact of this option on the accuracyof results, and especially on the estimation of potentialsavings? To answer this question, a set of representativehouses was selected, one for each construction period, withan energy consumption close to the average of the group.The potential energy savings, estimated by using the de-

Ž .fault values Default , were compared with those obtainedŽ .by using the monitored data Monit , assuming the renova-

tion will improve the quality of house up to the level ofŽ .present standard Table 10 . The difference between the

estimated annual energy savings varies between 33 and85% when the exterior walls are renovated, 27 to 85% forceilings, 77 to 85% for basement walls, and 17 to 104%when the air infiltration rate is reduced. When all therenovations are undertaken the difference varies between41 and 89%. For instance, the estimate of total energysavings of a house built in 1946–1960 is $670, usingmonitored data, and only $297 when the default values areused. The energy savings are then underestimated by about55%. These results indicate the use of default values canlead to large overestimates or underestimates of energysavings.

5. Conclusions

The proposed rating system uses an innovative ap-proach, in which the energy history of house is the firstsource of information to evaluate the index of energyperformance. The owner’s awareness could be increased

Ž .by the presentation of i the actual energy performanceŽ .compared with that of reference houses, and ii the poten-

tial savings, which can be obtained through the renovationof house or the change in people’s habits.

Other parameters such as the quality of heating equip-ment or appliances, or the quality of indoor environment

Ž .e.g., air quality, noise are also important for the evalua-tion of overall quality of the house. Presently, the proposedsystem addresses only the energy performance issue.

The proposed system could be viewed as very complexby those auditors using a simple check-list and a pointsenergy labelling system, or very simple by some re-searchers. In fact, this reaction was expected, since theproposed system tries to accommodate the two differentvisions, while dealing with the market forces, using avail-able techniques and facing some habits.

The application of proposed system to a sample of 45houses in Montreal indicated the approach can providereliable information in 5.2–5.5 h, at a cost of $533–568Ž .transportation cost not included . Some actions are recom-mended to reduce the time and cost of evaluation. How-

Ž .ever, only the market forces e.g., owners, banks, buyerswill finally control the cost, the duration and the neededaccuracy of the evaluation process.

The field study shows that one issue still remains to besolved in order to further reduce the cost of evaluation andto increase the accuracy of measurements. It is included inthis section, since the presentation could instigate otherresearchers to present their solutions or eventually to un-dertake new research projects. Since the thermal resistanceof exterior envelope plays a major role in the energyperformance of houses, there is a need for a faster andreliable measurement technique and equipment for theevaluation in-situ of the existing performance of buildingenvelope. The present standards cannot be applied forquick measurements. What is the cost effectiveness of thistype of measurement for the proposed system, when thefinal result is the estimated energy savings due to the

Žimprovement of some sub-systems e.g., walls, windows or.heating system ? Are all other parameters, used in the

evaluation process, of equal accuracy?

Acknowledgements

The authors acknowledge the support received from the‘Ministere des Ressources naturelles Quebec’ for this re-` ´search.


References

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Documents

Development of an energy rating system for existing houses