J. agric. Engng Res. (2000) 77 (4), 449}455doi:10.1006/jaer.2000.0624, available online at http://www.idealibrary.com onSE*Structures and Environment

00

Utilization of a Heat Pump in Pig Breeding for Energy Saving and Climateand Ammonia Control

Giovanni Riva1; Ester Foppa Pedretti1; Claudio Fabbri2

1University of Ancona, via Brecce Bianche, 60100 Ancona, Italy; e-mail of corresponding author: glriva@tin.it2Centro Ricerche Produzioni Animali, corso Garibaldi, 42, 42100 Reggio Emilia, Italy; e-mail: C.Fabbri@crpa.it

(Received 23 September 1998; accepted in revised form 2 August 2000; published online 22 September 2000)

The performance of three heating systems was analysed in closed-cycle pig farm (farrowing and weaningsection). Three adjoining rooms were heated using one of the following systems: a reversible air to air heat pump(HP) for both heating and cooling; a standard liquid petroleum gas (LPG) boiler for heating coupled withmechanical ventilation for summer cooling; and natural ventilation with emergency convective heating. Theirenergy consumption and in#uence on production parameters were compared.

Fifteen groups of sow and their litters were housed in succession in each room from the end of pregnancythrough weaning (5 cycles).

Temperature and humidity and production parameters (i.e. feed conversion index) were measured for eachcycle and room. In the case of HP, the ammonia emissions produced in, and extracted from, the breeding roomwere also determined.

The HP consistently maintained both temperature and humidity around optimal values (average 26)23C and64)2% relative humidity) and allowed primary energy savings of 11% compared with the LPG heater. Thepiglets weaned in the HP room showed better growth performance. Finally, the air processed by the HPcontained less than half the ammonia concentrations recorded in the naturally ventilated room.

( 2000 Silsoe Research Institute

1. Introduction

For pigs, especially in the weaning phase, a criticalparameter is room temperature, which must be main-tained around 263C (Whittemore, 1993). A further impor-tant variable is air quality (Drummond et al., 1980),which includes humidity and the dusts and gaseousmetabolites (such as nitrogen compounds and methane)produced by the animals themselves. Air quality iscontrolled by adjusting temperature, humidity andventilation besides ensuring the cleanliness of surfacesand limiting dejection retention on the #oor and inthe lower pit (Aarnink & Wagermans, 1997; Barberiet al., 1994; Bonazzi & Valli, 1993; Valli et al., 1994).Additional factors are: the protein content and amino-acid composition of the feed; the conversion coe$cientbetween the nitrogen contained in the feed and thattransformed into meat and/or milk; and animal type,weight and age.

21-8634/00/120449#07 $35.00/0 449

Besides adversely in#uencing production parameters,the gaseous emissions released into the atmosphere areamong the chief environmental problems connected withlivestock breeding, accounting for 75}80% of globalNH

3emissions in industrialized countries (Asman, 1992;

Isermann, 1990). According to a study by the DutchAgricultural Ministry in 1989, 37% of these emissionscome from animal enclosures and slurry storage; 51%from the distribution of animal slurry on the land; and12% from pastures. Hence, the widely felt need to reducethem, a measure which would both improve livestockperformance and reduce their environmental impact.

Based on these premises, the main objective of thepresent work was to evaluate and compare the perfor-mance of a heat pump (HP) with those of two traditionalheating/cooling systems in maintaining the main environ-mental parameters (temperature, humidity, ventilation andgaseous emissions) in a pig farm and to assess its in#u-ence on production parameters (Chiumenti et al., 1991).

( 2000 Silsoe Research Institute

450 G. RIVA E¹ A¸ .

2. Materials and methods

2.1. Housing and animals

The present data were obtained in the course of a2-year study (1994}1996) conducted with in the frame-work of a research programme on the correct utilizationof the HP.

The trials were conducted in a farm in Northern Italy(Po Valley; 80 km SE of Milan) producing heavy (170 kg"nal weight) pigs in a closed cycle (around 350 sows). Allanimal houses have natural or forced ventilation systems(axial fans) and slatted #oors.

Three adjacent rooms in the farrowing and weaningsection were selected for the experiment. In these roomsthe climate was controlled by one of these three systems:the HP, a conventional liquid petroleum gas (LPG)boiler heating system and natural ventilation.

Each room measured 5 m by 10)5 m and contained 12cages for as many sows. The farrowing unit (a smallportion of each room) is heated by electrical coils sup-plied by low-voltage current (24 V). The external walls ofthe building (25 cm in thickness) are made of brick plas-tered on both sides. The roof is made of prefabricated,reinforced concrete beams, with a ceiling in large brickplates (5 cm thick) layered with rock wool (about 4 cm inthickness). The roof sheeting is made of "brous concrete.The inner rooms are divided by brick walls (12 cm inthickness) plastered on both sides. The #oor is slatted,and the slurry collected in the pit underneath is continu-ously removed.

The air to air-type HP was manufactured specially forthis experiment. The slate air extracted from the enclosurewas used to heat incoming fresh air. The hot and damp airwas extracted, dehumidi"ed and cooled by an evaporatorcoil. The fresh and clean air was drawn over a condenserwhich heated it. For cooling, the cycle was reversed. Thecirculating #uid is the refrigerant R22. Temperature is ad-justed by the speed of the inlet fan, which is thermostaticallycontrolled. The speed of the extraction fan is manuallyregulated. The power requirement for the compressoris 1)9 kW; when the fans are included, the power suppliedincreases to 3)2 kW. The coe$cient of performance(COP) is 4)2 at the following reference temperatures: forheating, external air at 73C, evaporation at !53C andcondensation at 403C; for cooling, external air at 323C,evaporation at 103C and condensation at 503C.

The LPG boiler, which is ignited electronically, hasa thermal power output of 23)2 kW, high e$ciency(90)2%, checked value to fuel gas analysis) and is notendowed with a permanent pilot #ame. The boiler main-tains the temperature of a main circuit. The thermostatcontrolling temperature also operates a pump whichfeeds the metal pipes running under the slatted #oor.

A ventilation chimney is "tted with an axial fan of about0)5 kW.

2.2. Experimental design and measurement systems

Fifteen groups of sow and their litters were housed insuccession in each room from the last stages of pregnancythrough weaning (average cycle, 100 days). Environ-mental and production parameters were determined foreach cycle and room.

Monitoring of environmental parameters and datacollection were performed through a system installed ineach room consisting of: (a) six temperature/humidityprobes (Pt100/capacitance type: one room, one external,two inside the HP delivery and extraction ducts); (b)three electric energy meters connected to the electricalappliances (compressor and HP fans); (c) 3 h-countersand several on/o! sensors to measure the working time ofthe HP electrical motors (two fans and the compressor)and of the other fans; and (d) a personal computer (PC)equipped with two data collecting cards (Workmate;Strawberry Tree Incorporated) controlled by the Work-bench software. The equipment is designed for auto-restart to avoid data losses due to power failures.

The sampling interval was 10 min. The PC and theadditional "ttings were contained, together with anemergency battery, in a sealed control unit placed closeto the rooms.

To compare the electrical consumption obtained in theHP room with the electrical and thermal consumption inthe room LPG heated, a standard energetic unit is re-quired. Therefore, thermal energy and electrical powerhave been converted to kg of oil equivalent (kg [oe]),considering that: for the conversion value from thermalenergy to electrical power, the coe$cient is to equal 2)9;and, for the marginal electricity production, the e$ciencyof the system is equal to 43%.

The equipment used to evaluate ammonia concentra-tions was placed in the HP room. The air samplingpoints were upstream and downstream the machine. Theequipment consists of an adjustable-#ow sampling pump(up to a maximum of 0)01 m3min~1), which collects airthrough a plastic piping system. Up to eight bottles(bubblers) can be connected to the pump by means ofelectronically operated valves activated sequentially. Foreach sequence, the equipment controls the air volumesucked in and the volume normalized at a given airtemperature and mean #ow. Ammonia concentrationswere determined by means of a salt reaction with sulphu-ric acid in a 1% solution in distilled water. The studyprotocol envisaged monthly sampling periods of 24 hdivided into 3h cycles, which were carried out on threesuccessive days.

Table 1Temperature and relative humidity attained in the individual rooms (cycle averages) with the heat pump (HP), liquid petroleum gasboiler heating system (LPG) and natural ventilation systems (Standard) for conditioning the internal environment; given data are

average values$standard deviation

Cycle Temperature, 3C Relative humidity, %

External HP LPG Standard External HP LPG Standardsystem system system system system system

1st 23$6)7 27)2$1)7 26$3)5 27)9$3)0 69)7$17)9 62)6$9)0 67)6$8)8 66)1$6)82nd 7)5$4)6 25)8$1)9 22)1$3)3 23)9$1)4 82)2$13)2 61$7)5 70)4$12)1 62)4$5)53rd 11$4)7 25)8$1)5 24)5$2)4 23)3$3)2 75)1$23 58$14)8 63)9$12)8 65$12)64th 22)3$5)5 27)4$1)8 27)8$2)5 27)8$3)0 76)6$20)6 68)9$6)7 63)7$7)9 65)6$7)45th 13)9$6)5 26)2$2)2 25)6$2)2 25)9$2)4 87)1$16)8 68)6$11)4 68)6$7)8 69)9$10)5

HEAT PUMP IN PIG BREEDING 451

The number of animals and the presence or absence ofthe sow were recorded on each sampling date. At eachsampling, weight gain was determined on the basis of theinitial weight of litter.

3. Results

3.1. Environmental parameters and energy consumption

The average values of the environmental parametersdetermined in each room (Table 1) show that the averagetemperature was consistently closer to 26)53C in theroom "tted with the HP, whereas variations were widerin the other two rooms.

In the HP room, the consistently higher average tem-perature was associated with a decrease in average rela-tive humidity.

The total energy consumption of the HP was morethan 16 000 kWh (Table 2). Of this energy consumption,

TablWorking times and energy consumption

Cycle Temperature Compressordiwerence*,3C

Work time,h

EnergykWh

Energy,%

1st 2)5 989)4 2105)9 48)72nd 17)1 1423)5 2283)7 76)93rd 15)6 1162)4 1936)8 70)74th 4)9 892)5 2139)8 58)45th 11)8 848)7 1381)3 55)2

Average 10)4 61)98Total 5316)5 9847)5

*Di!erence between external temperature and HP room temproduction the e$ciency of the system is equal to 43%.

60)8% was attributed to the compressor (averagepower requirement of 1)9 kW) and 39% to the twofans. In particular, the inlet fan absorbed 3922 kWhand the extraction fan 2428 kWh. The consumptionof the LPG boiler was 22 026 kWh of gas primaryenergy and more than 1450 kWh of electrical energy(Table 3).

The saving in total primary energy (heating and cool-ing phases) obtained with the HP compared with theLPG boiler was about 229 kg[oe]yr~1 (11%), i.e. about9)7 kg[oe] per sow per yr. This estimate refers to the 2nd,3rd and 4th cycles, i.e. those in which both systems werein operation (Table 4).

The average COP of the HP determined for some&type-weeks' (Table 4) was 6)1. Although this value washigher than expected, it can be explained by the workingconditions of the machine (cooling of hot, humid air).Moreover, the COP closely depends on external temper-ature (Fig. 1): the lower the external temperature, higherthe COP values. This is because in the heating phase the

e 2of the heat pump (HP) (average values)

Inlet fan energy Extraction fan energy Total energy

kWh % kWh % kWh kg[oe] s

1344)2 31)1 870)9 20)2 4321)0 856)5257)8 8)7 426)2 14)4 2967)7 588)3463)4 16)9 340)0 12)4 2740)2 543)2

1104)9 30)1 420)3 11)5 3665)0 726)5751)8 30)0 370)6 14)8 2503)7 496)3

23)36 14)663922)1 2428)0 16197)6 3210)8

perature. s Taking into account for the marginal electricity

Table 3Energy consumption in the room using the liquid petroleum gas (LPG) boiler heating system

Cycle Gas consumption, m3 Gas primary energy, kWh Electrical energy Total primary energy,consumption, kWh kg[oe]*

1st 198)6 48)62nd 540 14 981 166)5 1309)93rd 193 5354 172)8 495)94th 61 1691 563)1 281)55th 350)7 86)1

Total 614 22 026 1451)7 2222)0

*The conversion value from thermal energy to electrical power, the coe$cient is to equal 2)9; and, for the marginal electricityproduction, the e$ciency of the system is equal to 43%.

452 G. RIVA E¹ A¸ .

evaporator is hit by damp, hot air, whose temperaturedoes not vary appreciably during the year (24}273C;humidity, 60}70%). Therefore, the cold source is espe-cially favoured from an energy point of view. In addition,the COP was calculated taking into account the energyconsumed by the fans. Energy consumption was higher inconnection with mild external temperatures because ofthe intermittent operation of the HP, and lower at coolertemperatures because of the almost continuous operationof the compressor. The primary energy conservation inthe heating phase was 39 kg[oe]. By contrast, the coolingperformance in the summer months was poor. Primaryenergy consumption in the cooling phase was29)3 kg[oe] per sow per yr.

With reference to ventilation, in the HP room, the airexchange was reckoned to be, on average, 11 and 15volumes per hour (1700 and 2400 m3 h~1) in winter andsummer, respectively. In the naturally ventilated room, itwas 2}3 volumes per h throughout the yr. In the LPG

TableEnergy parameters determined in the 9type: periods in the heat pum

Periods Thermal Electrical energyrequirements*, kWh

Compressor Coplus fan

17/10}23/10/94 #1605 24520/2}26/2/95 #2549 10813/3}19/3/95 #4909 38520/3}26/3/95 #4590 34317/7}23/7/95 !1777 28124/7}30/7/95 !1791 289

27/11}3/12/95 #5701 268

Av. values

*Positive values requirements in the heating phase; negative valtCooling performance.

boiler room, the axial ventilator guarantees an exchangeof 5 and 16 volumes per h in winter and summer, respec-tively.

3.2. Production parameters

The trial involved 1606 piglets.The weaning cycles hadan average length of 63 days, to which more than 30 daysof suckling and 4}7 days of the last phases of pregnancymust be added. The feed administered ranged from 25)1to 29)3 t (about 5}5)9 t per cycle).

The production parameters of the litters born andweaned in the three rooms are listed in Table 5. All thedi!erences in the parameters are statistically signi"cant,but it is possible to make some additional observations.The most interesting is the value of the feed conversionindex. The piglets in the HP room gained 0)467 kg per kgof ingested feed; for the animals in the other rooms this

4p (HP) room together with the coe7cient of performance (COP)

, kW HP thermal Average Averagecontribution, kWh COPs COPt

mpressoronly

166 1164 4)7 *

76 452 4)2 *

306 2970 7)7 *

262 2591 4)5 *

197 !438 * 2)2205 !321 * 1)6186 1772 6)4

6)1 1)9

ues requirements in the cooling phase. s Heating performance.

Fig. 1. Coezcient of performance trend as a function of theexternal temperature determined in the period from 13 to 26March 1995; each point represents the average value calculated

every 10 min of operation; R2, coezcient of determination

HEAT PUMP IN PIG BREEDING 453

index was 6)2 (LPG) and 9)6% (naturally ventilatedroom) lower.

A 20% reduction in mortality was also observedamong HP piglets, although the present sample is toosmall to allow any general conclusion.

3.3. Ammonia emissions

Lower ammonia concentrations were measured in theair processed by the HP (Table 6). Excluding the veryhigh values recorded in February (16)6 mgm~3), ammo-nia concentrations upstream the evaporator ranged from1)7 to 7)9 mgm~3 (2)9}13)7 p.p.m.). This is below themaximum value recommended for breeding rooms(20 p.p.m.).

Values per head are in#uenced by the fact that sincethe rooms were devoted to delivery/weaning, only thesows (or the sows with litters a few days old) were presentin any given room at some sample collections, and onlythe piglets at other times. Therefore, the data sometimesrefer to only 12 pigs, and other times to about 100. Witha view of improving data consistency and precision, the

TableProductivity results obtained in the thre

Room Duration of Pigs nurseds, Pigs deathss, Pigs wesystem weaning*, day head head hea

Heat pump 64$7 529 18 51LPG boiler 62$10 512 23 48Standard 62$17 565 22 54

*Data are average values$standard deviation. s Data are o

ammonia emissions of a single sow were also calculated.The data referring to live weight are less in#uenced bythese variations.

The measurements performed upstream from the HPyielded an average emission value of 22)4 g sow~1d~1,i.e. 123)4 g d~1 per t liveweight. These values are compa-rable to those reported for the Netherlands(7)9 kg sow~1yr~1) for a period of 350 days in traditionaldelivery rooms. This value is equivalent to 22 g sow~1d~1.

Downstream from the HP, emission values were re-markably lower, by generally more than 50% (Fig. 2). Inthe winter months, this may be attributed to the absorp-tion of ammonia during condensation on the HP evapor-ator as the extracted air is cooled. In summer, largeamounts of damp dust rich in ammonia nitrogen wereobserved on the exchanger itself.

It should be noted that the values observed in thesummer of 1995 (a particularly rainy period with temper-atures below seasonal averages) re#ect a lower amount ofwork by the HP which mainly worked as an extractor.Under those conditions the exchanger, hit by the incom-ing damp air, could be subjected to undercooling and,consequently, to a partial condensation.

With a view to better understanding this phenomenon,the condensation water collected in the cold periods andthe slurry (made up of water, dust and feed debris) sam-pled from the exchanger surface in the hot periods weresubjected to speci"c analyses. These showed very highN-NH

3concentrations: 315 mgkg~1 in the condensation

water and 3970 mg kg~1 in the slurry. The latter value isto be attributed to the small amount of water containedin the slurry and to its longer exposure to the air#ow.However, owing to the impossibility of quantifying thecondensation water and the dust produced during thecycles, this hypothesis cannot be tested in terms of massbalance. A 50% reduction in emissions due to the pas-sage through the HP seems unrealistically high. Thesevalues could be attributed to the sampling problemsencountered downstream the HP, since the high speed ofthe ducted air#ow may have undermined samplingaccuracy.

5e rooms; LPG, liquid petroleum gas

aneds, Weight increase*, Average Feedd weight* conversion*,

kg head!1 kg head!1 d kg kg [meat]/kg [ feed]!1

1 25)2$7)5 0)39$0)09 33)2$8)1 0)467$0)069 22)6$8)7 0)36$0)10 30)2$9)2 0)440$0)063 23)0$5 0)37$0)08 31)0$4)4 0)426$0)04

btained to the "ve cycle.

Table 6Ammonia emissions (monthly values); HP, heat pump

Month N}NH3 for HP NH3 emission N}NH3 for HP NH3 emissionupstream, mg m!3 downstream,

g t!1 d g sow!1 d mg m!3 g t!1 d g sow!1 d

December '94 4)5 127)7 19)2 2)5 67)3 10)1January '95 5)9 50)8 9)1 1)8 12)8 2)3February 16)6 107)3 26)2 * * *

March 4)8 162)4 24)9 2)3 71)1 10)9April 2)5 50)2 11)6 1)3 23)3 5)4May 6)3 176)1 34)8 3)3 88)1 17)4June 2)9 204)1 15)3 1)2 72)6 5)4July 4)3 141)1 20)9 2)6 476)5 11)3August 4)4 93)1 18)9 2)3 42)5 8)6September 7)9 159)7 19)5 2)9 53)0 6)5October 4)5 230)1 15)8 2)3 102)7 7)1November 1)7 31)2 8)6 1)0 13)0 4)8

454 G. RIVA E¹ A¸ .

When the reduction in ammonia emissions was relatedto some environmental parameters, a negative relationwas observed between the amount of air introduced forventilation and the decrease in gaseous emission. Bycontrast, a positive relation was found between thetemperature of the external environment and the temper-ature downstream the evaporator. However, as thisphenomenon is connected with the air characteristics andmachine operation, it should be considered as an overallvariable of these conditions.

4. Conclusions

The experimental utilization of the heat pump (HP) inthe weaning area of a pig farm demonstrated its ability tomaintain remarkably consistent values of the environ-mental parameters throughout its time of operation. Thiscontributed to keeping both temperature and environ-mental humidity around optimal values.

Fig. 2. Ammonia emission values in g t!1 liveweight per dayupstream and downstream of the heat pump (HP): , before HP

evaporator; , after HP evaporator

Compared with the liquid petroleum gas (LPG) boiler,the HP allowed to make total primary energy savings of11% (heating and cooling). With reference to productionparameters, the piglets born and weaned in the HP roomshowed better conversion indices, with respect to thepiglets located in LPG boiler room and in ventilatedroom. Finally, the air extracted by the HP contained halfthe ammonia emission of that from the naturallyventilated room.

The positive e!ect exerted by the HP on productionparameters compounds the favourable results of theevaluation of its performance in terms of both energyconsumption and reduction in gaseous emissions.

Acknowledgements

This work was sponsored by ENEL, Italy and CESI,Italy.

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