MEASURED ENERGY SAVINGS FROM OUTDOOR RESETSIN MODERN, HYDRONICALLY HEATED APARTMENT BUILDINGS

Martha J@ Hewett, George PetersonMinneapolis Energy Coordination Office

ABSTRACT

Since 1982 the Minneapolis Energy Office and Minnegasco have beentesting outdoor reset and cutout controls in modern, hydronical1y heatedapartment bui 1di ngs 0 The tests show that inmost buil di ngs the reset andcutout together reduce space heating costs by 10 to 20 percent with a paybackqf 1ess than one year@

An outdoor reset varies the temperature of the water in the heatingdi stri but; on system ; n response to outdoor temperature 6 An outdoor cutoutshuts off the circulating pumps and prevents the boiler from firing when theoutdoor temperature i s warm enough that no heat i s needed ~ Outdoor resetsthat contro1 the temperature of the bo; 1er water di rect ly were i nsta11 ed inthree bui1dings heated with gas-designed cast iron boilers, along wit~

outdoor cutoutSG The devices were evaluated by running the buildings alternate­ly under reset/cutout control and constant temperature control at two weekintervals over two heating seasons@ ual savings averaged 6700 Btu/sqft-yr,or 18% of annua1 space heat; ng costs ~ At the present pri ce of $0 <$ 585 pertherm, ngs in dollars ranged from $159 to $1393 per year~ The reset

together cost $450 installed, so in all cases but one thepayback was 1ess than one year 0 lim; ted tests compari n9 the reset

and cutout together th the reset alone were inconclusive~

Temperature data from 1ways, apartments and bo; 1er rooms i ndi catethat the outdoor reset improves the seasonal efficiency of the boiler,

heat loss from the distribution piping, and limits the tenants 8

to keep r apartments at excessive temperatures~

for cast iron boi 1er systems are supported byve other buildings in ich resets were

ldings already had cutouts, and the bo; water tempera-1 ng in the heating season before

the automatic reset devices were in a1-led, so the savings would be expectedto be somewhat less~ Savings averaged 6200 Btu/sqft-yr, or 10% of totalannual gas use (approximately 1 of annual space heating cost) ~ All fivebuildings paybacks of less than one year for the reset alonee

type of outdoor reset that mi xes hot bo; 1er water wi thwater to provide the desired supply temperature was installed

n9 heated by a steel fi re tube boi 1er 0 The bui 1di ng was runin manua1 reset mode and automat; c reset mode over one heat i n9

season~ Savings were estimated at 4600 Btu/sqft-yr or $1025, for a systemwi an installed cost of about $3000e

An outdoor reset is probably the most cost-effect; ve major rettofi t forhydron; ly heated apartment bui 1di ngs wi th cast iron bo; 1ers e Further workis needed to assess the cost-effectiveness for buildings with steel fire tubeboilerse C-135

MEASURED ENERGY SAVINGS FROM OUTDOOR RESETSIN MODERN, HYDRONICALLY HEATED APARTMENT BUILDINGS

Martha Jo Hewett, George PetersonMinneapolis Energy Coordination Office

INTRODUCTION

One of the major barriers to conservation investment in multifamilybui 1di ngs is the 1ack of re1i ab1e data on the say; ngs to be rea1; zed fromspecific retrofits. Since 1981 the City of Minneapolis and Minnegasco havebeen conducting a Multifamily Testing Program to field test specific conserva­tion measures in multifamily buildings. The research forms the technicalbasis for th~ City's multifamily conservation programo

Minneapolis has about 2800 multifamily buildings of five or more unitsoThese buildings comprise 51,000 dwelling units, or 32% of the city total &

Approximately 1200 of these buildings (21,750 dwelling units) were builtafter 1945 and are hydronically heated. The vast majori of these are threestory walk-ups. These buildings typically use about 50,000 to 80,000Btu/sqft-yr of gas for space heating, domestic hot water, stoves and dryers&

The physical characteristics of multifamily buildings and the owners'payback criteria make many envelope retrofits impractical e However, thereare promising heating system retrofitsG Results reported here show thatoutdoor reset and cutout contro1 ; s a hi gh ly cost-effect; ve' retrofi t formost hydronical1y heated apartment buil1dings in Minneapolis.

HYDRONIC HEATING SYSTEMS AND CONTROLS

Hydronical1y heated apartment buildings normally have one or more mainheat i ng di stri but ion loops, from whi ch separate baseboard loops run intoeach apartment ( gure 1) e3 A pump rcul es hot water through the rnai ndistribution pi ng continuouslYe Each apartment has a zone valve andthermostat to regulate the ow of hot water into its baseboard loop~ In themajor; ty of these bui 1di ngs in Mi nneapo1is, the bo; 1er i s contro11 ed by anaquastat which keeps the water in the system at a constant tempera~ureG

The amount of heat gi yen f by baseboard radi i on depends on thetemperature of t water circu ing through it~ uildings are typicallydesigned so a water temperature of 180 to 200°F is required to balance

apartments 9 heat 5S at the co1dest wi nter temperatures ~ . Thi s water~A~IA~W~~~1 is mu gran is needed for most of the winter$

oor reset varies he temperature of the water in the distribution"\lo~e.o y outdoor temperature, so that the mi nimum temperature

necessary to eat the bui 1di ng i s prav; ded (fi gure 2) ~ Di fferent types ofbo; 1ers requi re ffere methods of reset contro1e On a cast iron boi 1er,

outdoor can control the boiler w er temperature directly bycant 1i ng fi ng of the bo; 1er ~ B h mechani ca1 and e1ectroni c resetsare lable for this app · atione3 S el fire tube boilers, on the other

, must be kept 14 or hi gher to prevent carras; on and therma1~"ll"' __ 6!"6!" at could cause boiler failuree Reset control can be achieved byi nsta11 i ng a ee way mi xi ng va1ve that mi xes hot bo; 1er water wi th cao1er

w er to provide the sired supply te erature$ A more sophisticatedectronic reset must then be used to adjust the valve position in response

to outdoor temperature. (Another option is to install an on/off reset in

C-136

HEWETT ET AL.

ser~es with a low limit control to keep the boiler water temperature above140 F. This is cheaper, but sacrifices much of the resetting capability.)

In addition to the outdoor resets, outdoor cutouts were also installedand tested. Many hydronic heating systems are started manually in the falland turned off manually in the spring. Between these dates the pump operatescontinuously and the burners cycle to satisfy the demands of the aquastat orreset. Our; ng the spri ng and fa11 there are many mi 1d peri ods when no heatis needed, rang; ng from mi 1d days wi th co1d ni ghts to mi 1d stretches ofseveral days. It is not practical for the owner or maintenance person tostop and restart the boiler for every mild period, so the common practice isto allow it to run. An outdoor cutout deals with this problem by sensing theoutdoor temperature and automatically shutting off t~e burners and pumpwhenever heat is not needed. Cutout sett i ngs of 55 F were found to besuitable in the test buildings@

TEST BUILDINGS

The buildings used in the tests are generally typical of newer apartmentbuildings in Minneapolis, although probably somewhat better maintained thanaverage. They we're built between 1967 and 1973 and range in size from 9500

38, 000 square feet (12 to 45 un; ts). They have centra1, master meteredheating and domestic hot water and tenant metered electricity. Eight of thebuildings have atmospheric, gas-designed cast iron boilers, ranging in input

2 ,000 to 710,0 Btuh0 The ninth has a forced draft steel fire tubeboiler with an input 1,890 000 Btuh~ They are of wood frame construction

1; i ated walls roofse All have double azed windowso

GN

Outdoor resets and were i 1ed in three 1di ngs wi th castiron boilers (2631 2100, 3308) in the fall 82@ The heating systemswere run al with temperature control and reset/cutoutcontrol at two week ntervals over two heating seasons& For a limited period

ld in one 1 ng the reset/cutout mode was tested against theone0 A mi n9 valve and outdoor reset were installed in a

with a steel re tube boiler (2017) in the fall of 1983. Thewas run wi th and wi thout contro11 er

heat; seasonen9 between modes ed us to co11 ect data in both modes

comparable condi ons of weather, occupancy, maintenance and so onG Atwo week ; was chosen make the operating period long relative to

me res to stabilize in going from one mode to anotherto allow some me tenants to adjust their behavior to the new mode

each change, whi 1e st i 11 a11 ow; ng both modes to be tested duri nglar temperatures.

used by the bo; 1ers was submetered so that gas used for heatbe measured@ For the cast iron boilers, which had fixed firing

, i s was accomp1i shed by i nsta11 i ng an hour meter to record theburner ng time@ The steel fire tube boiler (which also heated thedomestic hot water) was already on a separate gas meter. Maximum/minimum ther­mometers were installed in selected hallways, apartments and boiler rooms to

C-137

HEWETT ET AlG

see how the two control modes affected building temperatures and jacket lossfrom the boilers~ SUbmete~s and thermometers were read weekly~

Temperatures of 165 F were suffi ci ent to keep the bui 1di ngs wi th castiron boilers warm in cold weather, so that setting was used for the constanttemperature mode throughout the heating season. The resets had fixed one-to­one reset ratios; that is, the boiler water temperature increased one degreefor each degree d~crease is outdoor temperature. The adjustable startingpoint was set at 95 F for 70 F outside temperatHre without causing complaintsfrom the tenants e The cutouts were set at 55 F0 In the bui 1di ng with thesteel fire tube boiler our agreement with the owner allowed him to adjustthe aquastat periodically, so we were in fact testing the automatic resetagainst a manually reset base condition. The reset itself had an adjustableratio and starting point, as well as night setback capabilitYG These wereadjusted periodically in response to complaintse Thus the supply temperaturein each mode did not follow a fixed curve but was somewhat erratice

Near the end of the fi rst test year one of the owners i nvo1'led i n thetesting program became so interested in the reset that he installed it infi ve other bui 1di ngs wi th cast iron boi 1ers ~ We have analyzed the month lygas data for these bui 1di ngs for a full year before and after .the resetswere in alled to supplement our detailed test datao These buildings alreadyhad cutouts, and pri or to the i nsta11 at i on of the resets, the bo; 1er watertemperatures had been reset manual1y· to some extent by the bui 1di ng care­takers~ These starting conditions, while not uncormJon in Minneapolis apart ....ment 1dings, were not exactly comparable to the detailed tests, andsomewhat lower savi ngs coul d be expected e These bui 1di ngs are referred tothrouhgout this paper as the me emental buildings ll

$

WHY IT WORKS:ICIENCY

OF RESET/CUTOUT ON SPACE TEMPERATURES AND BOl

The reset were expected to reduce energy use in several ways:1@ Reduci n9 overheat i "9 of apartments ~ Some tenants keep the; r apartmentsat exceSS1 'Ie temperatures, and may even open the wi ndow for comfort rather

turn the thermostat down ~ Wi th an outdoor reset, if the di stri but; onsystem is well balanced the water in the system will be just warm enough toheat apartment, enough overheat it or to keep it warm wi th

wi open * but i on system i s not we11 ba1anced, somewi 11 enough heat to keep them warm, whi 1e otherwi 11 access to enough heat to allow overheat i ng, if the

so chooses $ Apartments can a1so be overheated if the zone val ve i sstuck in an op position& An outdoor reset should greatly reduce the degree

in this situation.2~ Reducing overheating of the hal1ways~ In most hydronical1y heatedapartment Duildings the main distribution piping runs in the floor or

1i the ha11 @ Wi th the reset the water that ci rcu1ates i n theon 1 is er, especially in spring and fal1~ This should

overheating of the h 15 caused by waste heat from the piping.3~ Providing heat only when it is needed. Turning the pump and burners offduring mila periods is expected to provlde some savings~

4~ Increasing the seasonal efficiency of the boilerG Since the water in01 15 coo er on average, Jac e an s ac asses should be loweriron boilers only)~

HEWETT ET AL~

Limited budgets, staffing and access to apartments did not allow us tomonitor the entire building nor to collect temperature data at closei nterva1s. Therefore, the temperature data we have must be looked at assuggestive rather than definitive. Nevertheless, the data do verify that theabove effects are occurringo

Apartment temperatures were co11 ected in three un; ts i n bui 1di ng 3308duri ng part of the 1983-84 heat; ng season, and no di fference between resetmode and constant temperature mode was observed. Unfortunately the consump­ti on data for thi s bui 1di ng duri ng the same peri ad were so scattered thatdifferences in gas use were not statistically significant, so in retrospectthis building was a poor choice for testing temperature variations. That thereset can affect space temperatures i s demonstrated by experi ence in thefive supplemental buildingso All five buildings had tenant complaints of; nsuffi ci ent heat ri ght after the resets were ; nsta11 ed, and the resets hadto be. adjusted to provide higher boiler water temperatures until complaintswere mi ni mi zed e Wi th the i nformat i on we have at pres.ent it i s not clearwhether a reset is likely to reduce space temperatures in much of thebui 1di ng or on1y in those apartments that are a1ready margi nal1y heated due

low flow rates or insufficient fin tube radiation~

Hallway data show a consistent but small drop in temperature of 1 to ~

degrees in going from constant temperature mode to reset mode (figure 3)@No attempt was made to measure bo; 1er jacket 1asses di rectlye However,

is a 5 or 6 degree di fference in bo; 1er room temperature between thetwo modes ( gure 4), which suggests gnificant differences in jacket1osses ~ ue gas temperatures were measured at vari ous bo; 1er water temper­

a change of about one degree per degree change in boi 1er watertemperature was observed, a very minor effect0

METHODS OF ANALYSIS OF GAS USE DATA

A conceptual model of gas use as a function of temperature providesinto the behavior of the two control systems~ For this purpose it is

defi ne the bo; 1er 1cad as the amount of heat added to the waterme 0 The load thus inc1udes the heat necessary to ba1ance heat

the 1di ng the heat necessary to rnai ntai n the requi redin the stribution loop~

consi der constant temperature operati on 0 The load fmposed on theance loss building starts at zero at the balance

(where heat 1ass from the bui 1di n9 isba1anced by so1ar andi gai ns) increases 1i nearly wi th decreasi ng temperature ~ But thetota1 load on the boil er does not drop to zero at the ba1ance temperature,

constant temperature contro11 er forces the bo; 1er to rna; ntai nin the bution loop at the setpoint temperature, regardless

whether heat is needed or not& So above the balance temperature therea 1, nearly constant load to maintain the temperature of the

on water (figure 5)9Next cons; der reset/cutout operati on 9 The load vs e temperature curve

a somewhat fferent shape. At very co1d outdoor temperatures the loadd the same as wi th constant temperature operat ion, s i nee the water

temperature is the same~ But as outdoor temperatures become milder the resetreduces the di stri but ion loop temperature, thus reduci n9 the di stri but ionlosses and possibly reducing apartment and hallway temperatures as well ~ At

C-139

HEWETT ET ALo

an outdOOlotemperature of 550b the reset i s mai ntai ni ng the boi 1er water at

about 110 F, compared to 165 F for constant temperature operat i on ~ So theload imposed to keep the distribution loop warm is considerably lower. Werethe cutout not in place the reset by itself would continue to decrease theload as outdoor temperature increased, unt i 1 at an outdoor temperature of83 F the reset would be calling for 830 F w~ter and the load would be zero.But the cutout drops the load to zero at 55 F, abruptly truncating the loadcurve (figure 5).

Finally, note that jacket and stack losses in both constant temperaturemode and reset mode are approximately linear functions of load, so total gasuse (load plus jacket and stack losses) will have the same general shape asthe load curve, although the slope and position may differ.

Figures 6 through 9 show actual ~ata from the test buildings. The modeldiscussed above describes the data quite well. In constant temperature mode,none of the four bUildings for which weekly data were collected actuallyshowed a flattening of gas use vs. degree days at mild temperatures over theperiods of observation. This suggests that in constant temp&rature mode, theba1ance temperature for these bui 1di ngs is at or above 65 F. The data weretherefore fi t to a strai ght 1i ne ~ The reset plus cutout data showed a steepdrop near the cutout temperature in some cases but not in otherse These datawere therefore fi t to three di fferent mode1s to approxi mate the dotted 1i nein figure 5:

G .= a + b (DO)

G :: a + b (DO) + clOD

G :: a + b (DO) + c/D02

where

G :: average daily gas useDD :: average daily degree days (to reference temperature of 6SoF), anda, b, and c are statistically determined coefficients.

each building the model with the best t among those in whi~h all termswere cally gnificant was chosen*

The normal; d annual space heating use was calculated by mul plyinggas use at each degree day value by the normal occurrence of that value,

and then summing over all degree day values:

DDmaxNSHU:: I: G(DDi ) x normal occurrence of DO; ~

DOmin

OOm; n i s the lowest degree day va1ue for whi ch G(DO;) ; s greater than orto zero ~ The norma1 occurrence of DOi i s based on a 30 year average

( to 1980) for a heat; ng season runn; ng from October 16 to Apri 1 30 e

Based on our experience, this ·is a reasonable approximation of the datesthat mul family owners in Minneapolis turn their heating systems on andoff * Some owners run the system one or two weeks more on either end, butvery few run it any 1ess ~ Si nee the constant temperature and reset plus

C-l40

HEWETT ET ALe

cutout curves differ most in mild weather, defining the heating season thisway gives the most conservative estimate of savings from the reset and cutout@

Gas data from the five supplemental buildings were analyzed using apowerful computer model developed at Princeton University (Dutt, Fels, Gold­berg and Stram, 1982) ~ liThe mode1 assumes that energy i s consumed at aconstant rate (baseload a) when the temperature is above a certain point(reference temperature T), and below that point an additional constantamount of fuel (heating slope B) is consumed for each degree drop intempe~ature~1I While most conventional analyses assume a reference temperatureof 65 F, the Pri nceton mode1 fi nds the reference temperature that fi ts thedata beste

Once the program fi nds the best va1ues of a, B, and '", the norma1i zedannual consumption is calculated as:

where

H,.O (T) is the average daily heating degree days ton a normal year~

temperature '"

Thi s mode1 provi ded abuildings~

good t to from ve supp1ementa.l

SAVINGS

gures 6 through 9 show space heat i n9 energy use as a funct i on ofdegree days for 1 vely monitored buildings with cast iron boilersft

buildi 2631 and 2100 the consumption ata for t 0 years it thecurves, so data for b h years were grouped t ether for analys;sCl

3308 showed a si gni cant drop in consumpt i on for each mode from1 2, so the data for the two years were analyzed separately0owner reported i ng and repai ng a11 the zone va1ves, some of

which had been sti n9 in the open position, between the two heatingseasons~ In add; on, 4 of 12 changed occupants, and according to theowner new are more conserving~)

In constant is gnificant consumption even atzero i n plus cutout mode use drops tozero at day* For three of the cases the curves

and ly cross lower temperatures, as mi ght be expectedbo; 1er water temperature in reset mode exceed-~ that inconstant

"lI"'ft~i'llR~,1bI'lI~·l!"'aa%l''llA mode for au oor temperatures below about 0 F@ For the othercase the curves are nearl lel~

The i zed annua1 space heat; n9 use (NSHU) was ca1cu1ated based onve October 15 Apr; 1 30 heat; ng season (7637 FDD, compared

entire year) e The average NSHU for constant temperature,400 Btu/sqft and for reset plus cutout mode was 29,700 Btu/sqft,

ving an average savings of 6,700 Btu/sqft (table 1). [Using an October 1May 15 heat i ng season (7711 FOD) increases these numbers to 39, 100;

,700 8400 respectively~] Th~ savings for the indi dual cases were25~5%, 14@7%, 21~2%, and 9~8% of space heating gas use@ At present costs of$O~585 per CCF (hundred cubic feet), this represents annual savings of

C-f41

H'EWETT ET AL e

$1393, $527, $504, and $159 respectively (figure 10)$ For three of thesecases, the difference in consumption between the two modes is statisticallyhighly significant (p < .001). For building 3308 in the second year thedifference is not significant due to smaller savings and the large degree ofscatter in the datao

Analysis of monthly gas data for the five supplemental buildingssupports these fi ndi ngs Gl The bo; 1er water temperature had been reset man­ually to varying degrees in the heating season before the automatic resetdey; ces were i nsta11 ed, and a11 of these bui 1di ngs had cutouts to beg; nwi th, so the say; ngs woul d be expected to be somewhat lower 4 Say; ngs forthese buildings averaged 6,200 Btu/sqft, or 10% of total normalized annualconsumption (NAC) (table 2 and figure 11) Gl The difference between the preand post consumption was significant at the 5% level or better for three ofthe five buildings, but not significant for the other tWOe One building hadsavings of only 3.7%0 This building could not be reset nearly as far as theothers without causing tenant complaintse It is- possible that a few apart­ments had insufficient fin tube radiation or that the pump was too small togive adequate water flow under all conditions~ It is also possible at afew tenants preferred extremely high temperatures@ We hope to investigatethe causes of occasional poor savings with reset controls next yeare

Data from all ei ght' bui 1di ngs wi th cast iron boi 1ers were comb; ned toallow statistical analysise As has been noted, the ini al condition in thefi ve sup erne a1 bui 0 s was somewhat .. fferent from the base condi t ionfor the bui 1di in the i ens; ve test group @ The goa1 of comb; ned

s was to use all of e i nformat; on avai 1ab1e to us to put a lower1i t on the say; ngs that caul d be expected from the rese cutout, andan upper limit on the paybac The average savings the entire group were6,400 Btu/sqft-yr or 11 @8% of total annual gas usee Using a paired t test,the savi-ngs are 5i gni fi cant at the 1% 1eve1 or better 0 Tab1 3 presents

dence i nterva1s for the mean and for the samp1e assumi n9 a norma1stribution$ We would expect % of similar buildings in Minneapolis to

eve ngs between 2000 and 10,800 Btu/sqft ....yr, and 96% to have somengs0Energy use as a function of degree days for the building with the steel

re tube boiler is shown in gure 12e This building showed savings of 4600Btu/sqft-yr based on an Dc her 15 to April 30 heating season@ The dollar

are est; $1025~

none ui 1 (3308) cutout were tested agai nst theal e assess the effect cutout~ Although the data points for

the reset and cu were consistently below the line fit to the data forthe reset only, this partie ar building had so much scatter in the data

deviations due to cutout were not statistically significant~

; of the cutout depends on how careful the owner is in keepingthe nu er of weeks he supp1i es at to a mi ni mum, and on how abrupt the

0b seasons typically is~ In Minneapolis there are roughly 600 hoursabove 55 F between October 1 and May 15, but on1y 250 hours b ween October16 1 30 ~ We plan to conti nue recommendi ng the cutout cause it is

, it is more foolproof than ending on the caret er to turn theler off in the spring, and it probably does give some savings in mostldings$ We hope to be able to test it again next year$

C-142

Dunsworth of our staffs, and 0'8 Beller,

in preparing the final

HEWETT ET ALe

COST, PAYBACK AND INSTALLATION

The resets used on the cast iron boilers were simple mechanical-electri­ca1 contra1s wi th fi xed reset rat i os and cost about $250 i nsta11 ed 4) Thecutouts were also mechanical-electrical and cost about $200 installed.Simple electronic resets and cutouts are also available for about the samecost. Buildings 2631 and 2100 each showed paybacks of less than one year forthe reset plus cutout Ql Bui 1di ng 3308 showed a payback of 1ess than one yearbased on the fi rst year I s data, but 2e 8 years based on the second year 8 sdata. All five of the supplemental buildings showed paybacks of less than ayear for the reset alone (table 4)e

Assuming that future installations would include both the reset and thecutout (total cost: $450), and that savings could be conserva lyestimatedusing the per square foot data from table 4, over 90% of slmllar buildingsina11 si ze categori es can be expected to have a p.ayback of four years orless for the reset and cutout [figure 13)$

The electronic reset used on the steel fire tube boiler had anadjustable reset ratio and night setback capabilitY9 and was designed tocontrol a mixing valve0 With the valve itself and the plumbing required toinstall it, typical installed costs for this system would be abo $3000~

The part i 1ar ·t bui 1di ng used showed a payback of about three years, butit is impossible to generalize from it to a typical payback for this system@

The simpler, on-off resets and cutouts for cast iron boilers can be1ed by a competent heat i ng contractor e The more elaborate systems

fi re boi are genera1 i nsta11 by contractors cert i fi ed

ACKNOWLEDGEMENTS

would 11 to thank nnegasco for providi the for thisW'""JJ::flllO:~B:;Jfl~lr>rlll'1l~ In cular we wish thank hn Sweney and ichard Greenlund

us set up the proj and vi d Everetts for i nsta11 i ng thed or com techn; advice@

to thank t owners of the buildings for making their propertiesus and their ntenance staff caretakers for taking

t n90d thank

wi work

,Modelfor

s M@ L ~ Go1dberg and 0 e Stram, 1982 * The Scorekeepi ngConsumption: Procedures and Problems 0 Prepared

Summer Study, Santa Cruz, CA, August 21-28, 1982~

Gol , M0l0' 1982@ A Geometrical Approach to Nondifferentiab1e RegressionModels as ated Methods for Assessing Residential Energy Conservation~

PU!CEES Rep t 0 142, Center for Energy and Environmental Studies, Prince-ton versity, nceton, NJ0

C-143

r ic H Ii st

HEWETT ET AL~

Thermo~

MainOi stribution

loop

gure 1

aL~OJnstant temperature control0

i 180 II

110 II

e I150 I

Excessive t~perature150 leads to energy VlaSte

1l I

140Reset/cutout I

a!control I

I

130 II:n I

120 II

~I

1'10 III

100 I... I

! I90 I

II

-20 -10 0 10 20 30 40 50 60 70

td r

Figure 2

C-144

90

88

86

84

82

78

78

74

72

HEWETT ET AL~

Hallway Temperatureswith constant temperature and reset plus c~tout operation

+

u.. 882100-2nd WI. hallway0

ci 88

~ t H ttf'"":oJa; 84

+Jt ,~IlIllooCDa. 82 , +E ,!~

80tUit==«1:t: 76

2100-3ro flo hallway

~f74

,t H,72

~ ,ft ~70

+68

1-9 "T f P Io 10 20 30 40

Average Outdoor Temperature, of

80

18

18

74

72

70

68

j-10

3308-3rd fl. hallway

KEY

@ conatant temp.

II reset & cutout

I50

160

Each vertical line shows the max and min recorded over approximat@'y one week. Thecircle or square is plotted at the midpoint between mail and min.

Figure 3

C-143

110

100

~oi 90~1;~Q.

E(I)....E00a::

.! 80

'0m

10

60

Boiler Room Temperatureswith constant temperature and reset plus cutout operation

HEWETT ET AL~

-10 10 20 30 40

Average Outdoor Temperature, of

Ellen vertical iln19 IlIhO\llf$ thlll mall' ~nd min r@cordllld ov@,approximately on@ Wllllllk Th@ Clfch'l or IQUlllf~ III plotted

SlIt tho midpoint b@tw00n m8ll1! and min

Figure 4

50

Conceptual Model of Gas Use vs. Temperature8. Constant Temperature Operation b. Reset plus Cutout Operation

Average Daily Temperature

The soUd line rspreeente daily consumotion. The dashed line showlill theexpected curve when each data point represenU a period of several davs.

Figure 5

46

Space Heating Gas UseWith

Constant Temperature Operationand with

Reser Plus Cutout Operation

Averag_ DaUy De••• Days(ba•• temp = 85OF) :c

fT1:E:rr1--i--i

f"T1-i

»r-

10eofiO40

• constant _..-,et"r.

e = 13.78 + 0.4844 DDR2 = 0.046

II ,.s.' pmG cutoutG = 7.373 .. 0.61" DD - 82.15/00ft2 = 0.""

30

Average Dally Oegr•• Days(ba.8 temp. =eSOF)

Space Heating Gas Usewith

Constant Temperature Ope·rationand with

Reset Plus Cutout Operation

8lDG~ 2100. Years 1&2

o

o

40

60

30

u.UU

cD•:;)etilG 20

~-;0CDa«f

:0>-<

10

103GGO

II re.et pm. cutMI8.'33 .. 0.3301 DD - 127.1"00G••• l

40

@

263i~

30201@o

10

GO

u..,(,)(,) iO

••;:)••ei 40

~..0

• 30Q••:>-<20

10

gure 6 Figure 7

:::c.":£:fT1-I-t."-I

»r-

1060

• conlltant temperatureau: -0.6946 +0.392000R2 : 0.939

III re.et plus cutoutau: -3.837 + 0.44 2 200R2 : 0.863

II

Figure 9

20 30 40 60

Average Daily Degree Days(base temp.=85°F)

10

Space Heating Gas Use withonstant Temperature Operation

and withReset Plus Cutout Operation

BlDG. 3308. Year 2

o

10

40

o ,= . . . . . . .

U. 30(.)(.)

cD.,::)

(0

CdCJ

~OJo 20

CDCDasCD><:

1060

withra-·

• CORmtant tompou~tur@au: 2.129+ 0.47110DRI :0.871

Ii re••t plus cutoutau: -0.6740+ 0.461700R 2:0.e41

Gaslure

Figure 8

20 30 40 60Average Dally Degree Days

(base temp.=65Cf)

10

Ri

SpaceHeati.onstant Tern'..

and withPlus Cutout Operation8lDG~ 3308, i

o

o

40

La. 30(.)(.)

cDC1.t:l

C1.t«J

CJ

n ~! 'is.- C 20~ CD(X) 0

as~>0<

10

Savings from Reset a CUfout

HEWETT ET AL$

Intensively Monitored Buildings with Cast Iron Boilers

Energy Use

50

o

constant.temp control.·

roset PlusDcutout control

Annual Savings:Building 10:

Ar••,3q. ft.:

$13932631

25,300

$ 527 $ 504 $ 1592100 3308, yr 1 3308, yr 2

18,800 9600 9500

Figure 10

Supplemental Buildings with Cast Iron Boilers

ENERGY USE

before. after 0

Annual Savings:Building. 10

Area sq. ft.

$1286607

22.500

$454­2801

18 500

$3934416

15 400

gure 11

C-149

$937520

15 900

$259629

18 000

HEWETT ET Al~

aDG, 2011Savings

1080

• ftUlinlUlIl '0'01G =23.44 ... t.iS 7 400"'=0.1&2

III .'lItct,onlc '0&4181

Q =12.24 + 1.83800

""'=0.'.'Noll! bolle, &upp.kI. ePlAC0

heat iIllnd dOrRlUlUC hot 1I!6!l1!I$r.

GO

Steel Fire Tube Boller

40302010

180

140

120

•u..U(,) 100

tiet;:)

f$CIIi

60CJ

l;GJJ0$IG 60l3ilI~:>-<

40

20

Figure 12

----. ""',M (MaaRPayback)

10,000 16,000 20,000 26.000 30,000

Gross Building Area, Sq. Ft.

$for 41131.a",plo. assuming lla normal dhJtr.butlon, eo~ ofIIIllmllau bul.dlnge In Mlnn.aDolle Ar. 8Jlpocted to 'UIiYlIi li1payback equal to or better then 'li1li'U08 on thlllll cuno.

Figure 13

HEWETT ET AL3

Table 1. Energy use and savings datafor the foul" intensively IlI8Onitored buildings.

NSHU (CCF)1 NSHU/UNIT AREA (BTU/ft2) PERCENT DIFFERENCE

Bldg Test canst t reset/cutout canst t reset/cutout % ofa~~~~c31.0. Years IIXlde mode difference mode mode difference NSHU

2631 1&2 9328 6946 2382 36,900 27,SOO 9,420 25.5 20.1! 143 ! 119 + 184

(p ~.0010)2

2100 1&2 6141 5241 900 36,SOO 31,100 5,340 14.7 11.5:104 : 80 ! 140

(p< .00l)

3308 1 4057 3196 861 42,800 33,700 9,000 21.2 16.7! 127 ! 134 : 186

(p<.OOI)

3308 2 2772 2S01 271 29,200 26,400 2,860 9.8 7.7: 202 :172 :344

(.4<p<.S)

201742 16,219 14,467 1,752 42,800 38,100 4,620 10.8

! 649 ! 412 : 740

( .02<p<.05)

Notes: 1. Weather-normal ized annual space heati ng use. See text for calculation method.2. Probabil ity that the observed difference could Occur by chance when no real difference exists.3. See text for method of calculation % change in NAC from % change in NSHU.4. Values are for normalized winter gas use for both space heating and domestic hot water

by the main boiler.

Table 2. Enei'W use and savings datafor tmt five suppl~tal buildings.

NAC(CCF) 1 NAC/UNIT AREA (BTU/ft2)

PercentBldg censt t reset canst t reset Difference1.0. w/cutout w/cutout difference w/cutout w/cutout difference In NAC

507 13,474 11,280 2,198 59,900 50,100 9,170 16.3! 327 ! 326 + 483

(I' < :001)2

12601 10,301 776 60,000 55,800 4,200 7.0! 258 ! 360

(p .05)

144 9,189 8,518 671 59,600 55,200 4,350 7.3! 187 ! 438 :477

(.1< p<.2)

520 8,491 1,602 63,300 53,300 10,050 15.9:!: 275 ± 564

(.01 <p < .02)

629 12,089 11,646 443 67,300 64,900 2,470 3.7± 435 :!: 236 :!: 467

(.2 < p < .4)

Notes: 1. Total weather-normalized annual gas use. See text for calculaUonmethod.

2. Probability that the observed difference could occur by chance when no real difference exists.

Table 3. Sunnary statistics:savings for buildings with cast iron boilers.

Bldg. Chanae in Total Annual Consumption10 CCF percent ISIU/::.q .. t't ..

2631 2382 20.1 94202100 900 11.5 53403308, yr1 861 16.7 90803308, yr2 271 7.7 2860

507 2198 16.3 97702601 776 7.0 42004416 671 7.3 4350

520 1602 15.9 100S0629 443 3.7 2470

Mean 1123 11.80 6390Std. Deviation 758 5.66 3150Std. Error 253 1.89 1050Signif. Levell .OOl<p<.Ol p<.OOl p<.OOl

i 1 S.E. (870,1376] (9 .. 9,13" 7J (5340,7440]i",;i!-I! 80% (770,1476] (9.2,14.4] [4930,7850]

90% (653,1593] [8.3,15.3] (4440,8340]~.sJ! 95% (540,1703] (7.5,16.1] (3970,8810]

i~} 1 S.E. (365,1881] [6.1,17.5] [ 3240,9540]80% ( 64,2182] (3.9,19 .. 7] (2000,10789]

~j~ 90% [-288,2534] (1.3,22.3J ( 540,12240]95% (-629,2872] [-1.2,24.8] (-860,13640]

1I.~.~ 75% 588 7.8 4110=-}~. 80% 449 6,,8 3590

~~~ 90% 64 3.9 200095% -288 1.3 54

1.. Probability that these savings data could occur by chance whenno real savings exist.

2. For example, there is a 95% probability zhat the true meansavings are between 3970 and 8810 BTU/ft ..

30 For example, 80% of similar bUildings in Minneapolis co~ld beexpected to have savings between 2000 and 10,180 BTUfft .

4. For example, 90% of similar bUildings in Minneapolis could be2expected to have savings greater than or equal to 2000 BTU/ft 0

Table 4@ Simple payback estimates for the test buildingso

HEWETT ET ALo

Estimated Estimated EstimatedBldg. First Year First Year Simple Payback,I.. 0 ' Savings, CCF Sav;nQs $ Cost, $ Years

2631 2382 1393 450 0.. 3

2100 900 527 450 0.9

3308 yrl 861 504 450 OG9

3308 yr2 271 159 450 2.8

2017 1752 1025 3000 2.9

507 219'8 1286 250 0.2

2601 776 454 250 0.6

4416 671 393 250 0,,6

520 1602 937 250 0.. 3

629 443 259, 250 1.0

C-132