Field test on an exhaust air heat recovery heat pump

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Field test on an exhaust air heat recovery heat pump

BUILDING

RESEARCH

NOTE

r:.

_q;

{ E \ . J ~ ~ ~ ~ Q U E

.

!rn.

. - _izT

_{TEST ON AA EXHAUST}

_PUMP

R.X. Chauhan

I

D i v i s i o n of B u i l d i n g Research, National Research C o u n c i l of Canada

Ottawa, February 1985

I

FIELD TEST OM AN _{EXHAUST AIR HEAT RECOVERY REAT PUMP} by

R.B. Chauhan

ABSTRACT

This paper summarizes the results of the field testing of an Exhaust Air E e a t Recovery Heat Pump (EAHRHP) prototype which was installed in an unoccupied conventional house (House H3 of the BUDAC Mark X I Project Series), to determine its effectiveness as a supplementary heater, its effect on house a i r change rate and its overall performasce in actual use.

INTRODUCTION

A study conducted by Hooper and Angus 111 for the National Research Council i n d i c a t e d that an Exhaust Air Heat Recovery Beat Pump (EAHRRP) System should be a b l e t o reduce heating energy requirements in a house, improve indoor a i r q u a l i t y and reduce indoor humidity. As a result, t h e Division of Building Research commissioned ReepRite Inc. to design and b u i l d two prototype EAHRHP units based on the design parameters from the study done by Hooper and Angus Assoc. This f i e l d t e s t of one of these prototypes

was undertaken t o s e e how w e l l t h e _{prototype met t h e performance} expectations.

As shown in Figure I, the space heating EAHRHP is a single unit that is installed inside t h e house, It is an a i r t o - a i r heat pump recovering heat from the exhaust a i r stream. Heat absorbed by the evaporator coil from t h e exhaust a i r stream plus t h e heat of compression is transferred to the house, from the condenser c o i l . Heated a i r is introduced either d i r e c t l y fnto a r0Qm or into the a i r distribution system of t h e house.

Air _{is s u p p l i e d to the heat pump from the building space. The s u p p l y}

air temperature (Ti) is r e l a t i v e l y constant during t h e heating season, whereas the indoor relative humldlty (Elli) fluctuates with the rate of indoor moisture generation and t h e _{outdoor humidity}

_(RHO).

r a t e (VV) and the rate at which air exfiltrates through the building envelope

(VT

'

1.

Increasing the amount of air infiltrating into the house during t h e heating season by operating an exhaust fan, results in increasing the space heating load and decreasing the indoor relative humidity. Generally, if the natural ventilation rate is low, the relative humidity is high and there may be moisture-related building problems. In this case, the reduced RH is a d e s i r a b l e e f f e c t of the EAfIRHP, and reduced e x f i l r r a t i o n is also b e n e f i c i a l . The increased air infiltration, however, reduces the net energy savings of the E A R W .

DESCRIPTION OF W R H P PROTOTYPE

The prototype E A H W w a s 616 lam wlde x 687

mm

A summary of the components and d e s i g n conditions as provided by the designers [23 are as follows:

a) Evaporator c o t 1 consists of 5 rows of 9.52 mm diameter tubing w i t h f i n height of 203 mm and l e n g t h of 2 5 4 mm. There are 3.9 fins per a. Nominal air flow is 52 L / s at 60 Pa static pressure difference. b a t absorption rate is 2-7 kW at -20°C evaporating teqerature and air inlet temperature +20°C.

b ) Condenser coil consists of 5 rows of 7.94 mm diameter tubing with f i n height of 356 mm and length of 457 ma. There are 4.72 fins per cm. Nominal airflow is 260 L/s a t 60 Pa s t a t i c pressure difference. b a t rejection rate is 4.3 kW at 38% condensing temperature and air i n l e t temperature of +2D°C.

c ) Compressor is Tecumseh Model AB5527fI high e f f i c i e n c y R22 heat pump compressor with a nominal capacity of 7.9 kU.

d ) Blowers for both the evaporator and the condenser are single width, s i n g l e i n l e t type. The evaporator blower has a Torin 1060 housing with an impeller

160

three-speed motor i s capable of operating at 1330, 1140 and 1000 rpm. A t

1140 rpm it produces a f l o w of 52 LIB at 60 Pa static pressure difference.

The condenser blower has a Torin 1343 housing with a blower impeller 216 lam in diameter and 114 mm wide. The single speed direct drive motor runs at 1130 rpm, producing a flow of 269 L / s at 50 Pa static pressure difference.

e) Defrost timer l a a s o l l d s t a t e device which has been preset to provide a defrost cycle every 34 minutes. During a defrost c y c l e lasting

4.5 minutes t h e compressor is turned off and the evaporator fan

is

DESCRIPTION OF THE INSTALLATION

The EMHRW was I n s t a l l e d in a two-storey detached house located in

Orleans, near O t t a w a . The house has 118 m2 -of l i v i n g area and a f u l l basement with cast-in-place concrete foundation. This house had been modified to have a measured natural ventilation rate under calm wind

conditions of 0.5 ac/h at an outdoor temperature of -lSDC. Indoor space temperature was maintained at 20°C. The EAEIBHP was installed as the f i r s t stage of a two-stage heating system with the electric furnace acting as a backup. The beating system was controlled by a two-stage thermostat, with the EAlBHP having priority over the- furnace. The furnace fan

ran

continuously to provide cdnstant a i r circulation.

Stage

I

s a t i s f y the space heating requirements and f f the heat demand w a s higher than the output of Zhe

EAHREP,

This control strategy is ahown IZn Table 1.

The EMRIP and furnace interconnection is shown in F i g u r e 3. The exhaust air is drawn from the heated space (basement) at @ rate of 57 L/S

and the flow over the condenser is drawn from the basement at a rate of 191 L / s . !fhe heated air from the E m P condenser is then discharged into the return a i r plenum. The furnace fan is run continuously to allow for the distribution of the heated a i r s u p p l i e d by the EAHEW.

The heat supplied by the EAHIUP was measured by fitting the insulated condenser discharge duct with a d i f f e r e n t i a l thermopile to masure the temperature difference between air in khe duct and the basemeat air. The output of the thermopile was connected to an integrating counter, This counter had been calibrated a t an airflow rate of 191 L I s over the _condenser cot1 to produce a pulse of the counter for every 170 kJ of heat supplied to the house.

I

TESTS CONDUCTED

The t e s t was carried out over a period from Dec. 2 4 , 1983 to May 10, 1984 w i t h some gaps, since t h i s house was also being used for some other t e a t s .

Monitoring of the EAHRWP and furnace energy consumption was done by reading the kWh meters once a day at 1400 hours.

Tests were conducted t o tmnitor the energy consumption af the EAHRHP and furnace in various operating modes over the duration of t h e test period.

a) During s e l e c t e d periods, the EAHRIIP was turned off and the energy used by the furnace was recorded.

b) Energy consumed by the furnace and EAHESP was recorded when the house was heated by this combination.

c) P e r i o d i c checks of EABRHP performnce were done t o d e t e d n e a i r temperature and volume of a i r flowing across It, This a l s o confirmed that there were no changes i n the conditions under which the EAHRHP was operating

.

d)

The

duration of the t e s t period. These Peasurements were done during varying outdoor conditions and under situations when the EABRBP was runrifng and when it was not running.

Weather information used for analysiug the t e s t results was obtained from the Ottawa Internatllonal Airport weather o f f i c e .

TEST RESULTS

Figure 4 shows the electric energy consumption

of

EAEIRHPlf uraace combination than it is with the furnace alone. Above the balance point, the furnace component of electric consumption consists OE the

furnace fan energy, since the fan ran continuously. Table 2

shows

of

The electric energy consumption curve for the

EAHRHP

difference

(ATi,)

Figure S shows the sir change rate of the house at d i f f e r e n t

ATio

conditions when the EAHBlHP is tunriing and when it is off. This shows that

a t a ATi,

of

EARRHP is o.£f, i . e . , evaporator (exhaust) fan is o f f . This a i r change rate rises to about 0.67 ac/h when the EAHRHP is running. This increased

i n f i l t r a t i o n increases t h e heating laad due to i n f i l t r a t i o n by ,about 30%. The coefficient of performance (COP) is deftned as the r a t i o of heat output t o the work input 131. The- work input c~dsists of energy used by the EAHREIP (i.e., by the compressor, fans and controls)

(E

The

:

m COP

-

"

PELP

-

7

-

5

Figure 6 shows the d a i l y average COP of the ISAHRHP with respect: to ATio. The COP is essentially constant over the range of operating

temperature conditions. &frost cycles are initiated after every 34 minutes of continuous operation. At outdoor temperatures below 3'C, the compressor runs continuously. Thus t h e effect of defrost cycles is a s l i g h t

degradation in EAHREiP performance when operating below the balance point, Since the UHREiP _{is operati= indoors and the evaporator is exposed} L O

air at room temperature {approximately 2 0 O ~ ) the evaporator load on the compressor does not fluctuate much, which in turn means that t h e compressor power draw remains s t a b l e . This suggests that the COP would be f a i r l y constant aver t h e heating season and the test results seem to confirm t h i s .

COMPUTER SI?WIATIONS

FOR

E M P ,

a i a l a t ions using an in-house computer program were performed [EAST Build'fng Heating Load Calculation Method by D. Sander]. The simulated performance of

the EAHRHP in the t e a t house for various climatic locations is l i s t e d fn Table 3.

The simulations indicate that the EAEiRFIP c o u l d reduce purchased heating energy requirements anywhere from 25 to 48%, depeadfng on severity of l o c a l

climatic conditions. This saving could be further

increased

coefficient of performnce was raised by an Improved d e s i g n . However t h e absolute savings in electrical heating energy is about 5 MWmh per house per season in all regions.

C O W N T S ON

FIELD

The installation, w i r i n g and controlling of the EAHRHP in the t e s t house was f a i r l y etraightforward.

Onc& i n s t a l l e d , the EAHRtIP operared without any problems. The defrost system worked well and it was easy t o dispose of the condensate via the basement drafn or through a laundry tub l o c a t e d nearby. The aperatfng n o i s e l e v e l of the EAFIRFiP _{was not high.}

_It

system sound levels.

The exhaust a i r heat recovery heat pump d i d perform as predicted in the Hooper, Angus report, although at a lower c o e f f i c i e n t of performance, and with more defrost cycles. The EAHRBP w a s effective in supplying a

signff icant portion of the heating energy i n the t e s t house, with an increase in the base i n f i l t r a t i o n rate of the house.

Computer sirmrlations indicate that the

EAHRHP

electric heating energy consumption by up to 48X depending on local climatic conditions, and it can supply up t o 972 of the required seasonal heating energy in m i l d e r climates.

ACKNOWLEDGEMENTS

The author wishes t o acknowledge the technical assistance of

David R. Wright in instrumenting the project. The author also wishes to thank

Dr.

Dr.

REFERENCES

1 . Booper and Angus Associates, Development of an Exhaust Air Beat Recovery Heat Pump: A Study.

DBR

2. Blackmore, G.R., Design, Construction and Testing of Prototype Exhaust Air Heat Recovery Beat Pump, KeepRite Inc., DSS Contract

No. OSX83-00013, Brantford, Ontario, January, 1984.

3. Sauex, H.J. and Howell, R.H., Heat Pump Systems. John Miley and Sons, Elew Pork: Toronto, 1983, 7 2 1 pp.

Table 1:

E~REPIFURNACE

Component Cycle Cycle

Thermostat

S t a g e 1 Evap Fan ON-OFF OM

Cond Fan OM-OFF OFF Above

Compress or OM-OFF OFF Balance

Furnace Fan ON ON Point*

Furnace OFT OFF

Stage 2 Evap Fan ON ON

Cdnd Fan OW OFF B e l o w

omp pressor

Furnace Fan OW ON Point*

Furnace ON*FF ON-OFF

*Balance p o i n t is the outdoor temperature above which t h e EAFIREIP can supply all the heating requirements of the dwelling.

Table 2: COMPARISON OF HEATING ENERGY CONSUMETION WITH (EAHRIIP

+

Indooroutdoor temperature difference

K

k~ .hiday kU* hiday

(

&DdUC-

A

Table 3: EAIIRHP COMPUTER SIMULATIONS FOR VARIOUS CANADIAN CITIES

Air change/bour base = 0.47 average; Internal g a i n s = 1.0 kW Air changehour w l t h EAHRHP = 0.63 Average

Vancouver Summerland Halifax Toronto O t t a w a Edmonton 2623 D P 3313

D W

3317

EAHRHP,

1

1 ,

4, Hear reqd i n base hause

1

5. Purchased energy f o r ElllLRHP at: COP 2.2 =

[ ( 2 ) 5 2 . 2 ] , kW*h 6. Total purchased energy [ (1)+(5)

1,

purchased enerw due

9. % of total heating supplfff by EAHRllP

d

-

_I

10.

Z

load due t o higher 12

\

OUTDOOR

AIR

COND ITION

T o , RHO)

f

A I R EXflLTRATlON

v;

T.

l NDOO R TEMPERATURE

To

OUTDOOR

TEMPERATURE

RH-

INDOOR

RELATIVE HUMIDITY

RH

OUTDOOR

RELATIVE HUM1

D

ITY

0

Q~

P

HEAT

DELIVERED BY EAHRHP

Qe

HEAT

GAIN

AT

EVAPORATOR

E~~

ENERGY

USED

BY

EAHRHP

v~

TOTAL

RATE

OF

A I R

lNFlLTRATlON

vv

FORCED

VENT

I

IATI

ON

R A E

'i

RATE

OF

A I R

EXFILTRATION

F I G U R E 1

ROOM

- A I R

FLOW

20°C

57

L l s

ROOM

-

A I R

FLOW

mOc

191

Ils

F I G U R E

2

R E F R l

G E R A T I O N S C H E M A T I C

SUPPLY RETURN EXHAUST F I G U R E 3 EAHRHP A N D FURNACE INTERCONNECTION F I G U R E 4

I 1 I I

0 EAHRHP FAN ON

10 20 30 40 5 0

INDOOR-OUTDOOR TEMPERATURE DIFFERENCE, K lDA l LY AVERAGE)

F I G U R E 5

A I R CHANGE R A T E W I T H E A H R H P

INDOOR-OUTDOOR TEMPERATURE DIFFERENCE, K IDA t LY AVERAGE)

COEFF I C IENT

OF

OF