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Technical and economic feasibility of a geothermal facility for air

conditioning of an intensive piggery

J. Lampurlans Castel(1)

, C. Flament Maci(1)

, Ll. Puigdomench Franquesa(1)

(1)E.T.S. dEnginyeria Agraria, Av. Rovira Roure, 191.

25198-Lleida (Spain)

Phone Number: ++34 973 70 25 37

e-mail: jlampur@eagrof.udl.es

1. IntroductionIn his last report (2007), the Intergovernmental Panel on Climate Change (IPCC) [1] predicted an increase

of 0.5 to 1.5 C in the mean temperature in the European area for the period 2020-2029. Recently [2],

conventional technologies used today for air conditioning intensive piggeries were tested under a 2 C

temperature increase scenario. This rise of temperature resulted in an increase of the cooling needs thatwere not sufficiently covered with natural ventilation. Accordingly, a shift to the use of forced ventilation

and evaporative panels was predicted for the near future. As an alternative, in this study we evaluate the

technical and economic feasibility of a very low temperature geothermal facility.

2. MethodologyTo develop this study we selected a representative intensive piggery for piglet production in the Ebros

Valley. The piggery is situated at Candasnos with mean extreme temperatures of -3 C in January and

34,6 C in July. Mean relative humidity was 84.2% in January and 57,4 % in July.

The piggery has three buildings (Fig. 1): one for sows waiting for service (Mounting), another for

gestating sows (Gestation), and a third one for the sows and their piglets (Maternity).

Fig. 1. Piggery buildings with the enclosures considered for thermal loads calculation.

The external walls are made with triple hollow ceramic brick externally coated with white cement and

internally insulated with polyurethane foam (overall coefficient of heat transmission, U = 0.53 Wm-2C-

1). The cover consist of corrugated fiber cement roofs insulated with polyurethane foam (U = 0.64 Wm-

2C

-1). There are polyester doors (U = 4.72 Wm

-2C

-1) and polyester or glass windows (U = 5.75 Wm

-2

C-1

) on the walls. The surfaces of each element are shown in Table 1.

Table 1. Surface of the different elements at every building.Building External walls

(m2)

Cover/roofs

(m2)

Doors

(m2)

Windows

(m2)

Mounting 276 473 8 23.9

Gestation 351 675 6.4 11.5

Maternity 258 675 8 11.5

Maternity (582 m2) Gestation (540 m2) Mounting (378 m2)

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Air was conditioned by natural ventilation with manual operated windows in Mounting and Gestations

buildings. In the Maternity building, with the highest environmental requirements, forced ventilation and

evaporative coolers were used. For the piglets, heating elements were also installed. Mean temperatures

inside de buildings obtained with these systems in winter and summer are shown in Table 2.

Table 2. Mean air temperature inside the buildings.Building Inside winter

temperature (C)

Inside summer

temperature (C)

Mounting 10 32

Gestation 14 32

Maternity 21 31

For the design of the new geothermal facility, the environmental animal needs in every building were

defined to assure its comfort (Table 3).

Table 3. Environmental conditions to be attained in every building.Building Inside winter

temperature (C)

Inside summer

temperature (C)

Relative humidity

(%)

Air velocity (m/s)

Mounting 15 28 70 0.2-0.7Gestation 15 28 70 0.2-0.7

Maternity 20 25 60 0.2-0.5

According to the meteorological data, mean of maximum air temperatures was the highest in July (34.6

C) and mean of minimum was the lowest in January (-3.0 C). Mean air relative humidity was 57.4% at

24.1 C in July, and 84.2% at 4.2 C in January.

Heating needs (Qheating) in winter were computed as

Qheating = Qenclosures transmission + Qventilation - Qanimals

In summer, the cooling needs (Qcooling) were determined

Qcooling = Qenclosures transmission + Qsolar radiation + Qanimals Qventilation

Thermal animal loads were calculated according to animal condition and number at every building (Table

4). Minimum weight and number were considered to determine heating needs and maximum to determine

cooling needs.

Table 4. Minimum and maximum weight and number of animals at every building.

Building

Minimum

weight

(kg)

Maximum

weight

(kg)

Minimum

number of

animals

Maximum

number of

animals

Mounting 180 190 120 138

Gestation 210 220 214 216

Maternity 195220 50 60

To reduce the thermal loads due to ventilation, needs of ventilation were computed as the minimum

necessary to maintain relative humidity below the established limits (Table 3).

Once the maximum heating and cooling loads were determined geothermal air conditioning system were

designed for every building including fan-coils inside the buildings, water-water heat pumps and verticalgeothermal proves. Fan-coils worked with 50 C water in winter and 7 C in summer. Head pumps were

designed to work between 50 and 2 C in winter and between 7 and 30 C in summer. The vertical

geothermal proves (double U) were designed following the ASHRAE manual (1995) [3] assuming a

constant soil temperature of 15 C (the mean in Spain below 5 m) and a thermal gradient of 10 K. Proves

were installed in 100 m wells.

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Finally, an investment analysis was conducted to ascertain the economical feasibility of the new

installation. As the new installation improved the inside environmental conditions, and increase on the

productivity was expected. The productivity increase that made the investement profitable was calculated

according to the Net Present Value, the Internal Rate of Return and the Payback Period, considering 40%

of the investment being subsidised by the government.

3. Results and Discussion

Air conditioning needs varied with building type and year season. In winter (Table 5), the highest needswere in Maternity and Gestation buildings. In Mounting and Gestation buildings, ventilation loads were

the highest whereas in Maternity enclosures transmission loads were the most important. In summer

(Table 6), the most important thermal loads were produced by the animals inside de buildings. Cooling

needs were the highest in Gestation building. Heating needs were higher than cooling needs, especially in

the Maternity building, and determined the power of the geothermal facility.

Table 5. Winter thermal loads and heating needs at every building.Building Enclosures

transmission

(kW)

Ventilation

(kW)

Animals

(kW)

Heating needs

(kW)

Mounting 29.2 42.5 -34.1 37.6

Gestation 41.6 89.7 -72.1 59.2

Maternity 52.7 30.8 -23.5 60.0

Table 6. Summer thermal loads and cooling needs at every building.Building Enclosures

transmission

(kW)

Solar radiation

(kW)

Animals

(kW)

Ventilation

(kW)

Cooling needs

(kW)

Mounting 2.5 4.1 40.9 -12.6 34.9

Gestation 2.8 2.1 75.3 -23.2 57.0

Maternity 5.2 2.2 30.0 9.2 46.6

The unit power and number of fan-coils need in every building are shown in Table 7. As the Maternity

building was subdivided in 5 parts, the number of fan-coils had to be a multiple of 5.

Table 7. Fan-coils power and number at every building.Building Unit power (kW) Number Total power (kW)

Mounting 5.00 9 45.0

Gestation 9.50 7 66.5

Maternity 6.99 10 69.9

Table 8 shows the heating and cooling power and the efficiencies of the head pumps for every building.

The highest powers were needed for the Gestation and Maternity buildings. The efficiencies fall in the

typical range for heat pump in geothermal facilities.

Table 8. Head pump heating and cooling powers and efficiencies at every building.

BuildingHeating power

(kW)

Power consumption

when heating (kW)COP

Cooling power

(kW)

Power consumption

when cooling (kW)EER

Mounting 37.6 11.4 3.3 34.9 8.0 4.4

Gestation 59.2 18.8 3.1 57.0 14.2 4.0

Maternity 60.0 19.1 3.1 46.5 10.6 4.4

COP, Coefficient of Performance

EER, Energy Efficiency Ratio

The pipe length and the number of geothermal double U proves (wells) needed at every building areshown in Table 9.

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Table 9. Length and number of geothermal double U proves at every building.

BuildingPipe length

(m)

100 m wells

(number)

Mounting 685 4

Gestation 1057 6

Maternity 1072 6

The total investment was of 311,455 . The 40% of them was considered to be subsidized by the

government. The effect of the piglet production increase on the investment evaluation indexes is shown in

Table 10.

Table 10. Piglet production increase effect on investment evaluation indexes.Piglets production increase (%) 3 4 5 6 7 8 9 10

Net Present Value (x1000 ) 18 75 133 191 249 307 365 422

Internal Rate of Return (%) 3.2 6.9 10.3 13.3 16.3 19.1 21.8 24.4

Payback Period (years) 14 11 9 7 6 6 5 5

According to these results, the inversion is profitable with production increases above 3%. A 5%

increases can be expected due to the improvement of the environmental conditions which would justify

the investment with an Internal Rate of Return of 10.3%. However, these results are very dependent on

the government subside which can be suppressed, especially in the current crisis context.

4. Conclusions

The geothermic air conditioning of an intensive piggery is technically possible obtaining high efficiency

indexes. Provided the 40% government subsidy persists and a 5% increase of production or more is

achieved, it is also economically feasible.

5. References

[1] IPCC, 2007. Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to

the Fourth AssessmentReport of the Intergovernmental Panel on Climate Change [Core Writing Team,

Pachauri, R.K and Reisinger, A.(eds.)]. IPCC, Geneva, Switzerland, 104 pp.

[2] V. Valio, A. Perdigones, C. Porras and D. Alcal, 2009. Efectos del calentamiento global: viabilidad

futura de los actuales equipos de refrigeracin para naves ganaderas. V Congreso Nacional y II Congreso

Ibrico Agroingenieria. Lugo 28-30 september.

[3] ASHRAE, 1995. Commercial/Institutional GSHP Engineering Manual.