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Wine cellar modeling for the assessment of energy efficiency
Stefano Benni, Federica De Maria, Alberto Barbaresi, Daniele Torreggiani, Patrizia Tassinari,
University of Bologna - Department of Agricultural Sciences, Viale G. Fanin 48, 40127 Bologna (Italy)
Abstract
In wine productions, temperature control of the wine-making process and the built spaces
intended for conservation and aging represents one of the main factors of energy consumption. Consequently, the rising energy costs entail a drag on competitiveness of farms. Therefore farmers and producers, as well as public institutions concerned, are interested in the
research of constructive solutions and systems that maximize energy efficiency of buildings
and facilities, through the optimization of the respective thermal control.
This study is part of a broader research aimed at the definition of optimized buildings-design
criteria for farm wineries, in terms of functional layout and energy efficiency. This research
involves the evaluation of the energy performance effects of various design choices, such as
location, orientation, building technologies, materials, and technical solutions. In particular,
The purpose of this study is to assess the energy efficiency of different design solutions for
wine storage, through digital modelling and thermal simulations.
We considered a case study represented by a farm winery located in the Imola district (Emilia-Romagna, Italy), whose farmstead consists of several buildings hosting different activities
of the production process: wine-making, storage, aging, commercialization, and services.
During one-year period of monitoring, the outdoor climatic parameters and the indoor thermo-hygrometric data were recorded, respectively through a meteorological station
located outside the winery, and data-logger sensors. The built system was surveyed and the
storage building, which is the focus of this study, was modelled using Open Studio program.
The numerical model was based on the definition of suitable thermal zones, i.e., volumes of
air at a uniform temperature including their boundary surfaces having defined properties of
heat storage and transfer. The model was integrated with the climatic parameters and the
indoor thermal data, which defined the boundary conditions, and then imported into the thermal simulation program Energy Plus. This software can calculate the heating and cooling
loads necessary to maintain thermal control setpoints in buildings. For this purpose, we created suitable libraries of building materials, both traditional and innovative, through the specification of the characteristics inherent to the thermal behavior (thickness, density, conductivity, and specific heat). The considered materials include cement plaster, masonry of bricks or
hollow bricks, polyurethane, coniferous wood, with various geometric configurations.
On the basis of the resulting models , we compared the current conditions of the building with
different stratigraphic compositions of its envelope, identifying those materials which can be
used as integration or replacement of the existing building envelopes, to help maintain constant levels of temperature and humidity, suitable for conservation of wine, while minimizing
the energy needs.
This methodology proved suitable to guide the choice of building materials and technical solutions in the design of new wine storage buildings, and in the thermal adaptation of existing
ones, identifying the most energy-efficient solutions.
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Keywords: energy-efficiency, modelling, monitoring, farm winery
1.
Introduction
In wine production, temperature control of the wine-making process and the built spaces intended for conservation and aging represent one of the main factors of energy consumption
(Benni et al., 2013). Consequently, the rising energy costs represent a drag on competitiveness of farms. Therefore farmers and producers, as well as public institutions concerned, are
interested in the research of constructive solutions and systems that maximize energy efficiency of buildings and facilities, through the optimization of the respective thermal control
(Barbaresi et al , 2014).
This study is part of a broader research aimed at the definition of optimized buildings-design
criteria for farm wineries (Torreggiani et al., 2011; 2014), in terms of functional layout and
energy efficiency. This research involves the evaluation of the energy performance effects of
various design choices, such as location, orientation, building technologies, materials, and
technical solutions. In particular, this paper focuses on the energy retrofit of existing buildings
for wine production. The purpose of the study is to assess the energy efficiency of different
design solutions for wine storage, through digital modelling and thermal simulations.
2.
State of the art
In winemaking, the storage phase with the simultaneous refinement of the product, as well as
the aging process, whereas required, play a primary role for product quality. As ambient micro-climate has a fundamental influence in such processes, several researches have aimed
at defining the optimal thermo-hygrometric environment for wine storing and aging. These
studies usually define thermal intervals: Marescalchi (1965) indicates 15°C to 20°C for the
first year of wine aging and 4°C to 12°C for older wines, Troost (1985) suggests 9°C to 12°C
for white wines and 12°C to 15°C for red wines, Bondiac (1980) recommends 10°C to 12°C,
and the Hong Kong Quality Assurance Agency (HKQAA, 2010) recommends 11°C to 17°C
for fine wines. Previous studies also underline the importance of a constant temperature:
Vogt (1971) recommends that the yearly temperature oscillation not be greater than 5°C to
6°C; and Ruiz Hernández (1999) and Zamora (2003) warn about the risks in wine aging due
to high oscillations and high temperatures in summer. These studies also indicate the absence of conservation problems at low temperatures and increasing risks for temperatures
higher than 20°C (Ribéreau-Gayon et al., 2002).
The indications provided by broad literature on this issue can be summarized by defining
suitable temperature ranges to reduce the loss of wine in the barrels and to ensure a sufficient quality of the product. Such temperature should be between 9°C and 17°C and must
not exceed 20°C, while the oscillation of the annual temperature should not exceed 6°C 7°C. For this reason since ancient times, wine has been stored in underground rooms, able
to satisfy these conditions all year round (Alberti, 1565; Palladio, 1570; di Giorgio Martini,
1967). Currently, however, trends in the building sector have been focusing on aboveground
structures, to reduce the initial costs of construction, but making it necessary to have control
systems for indoor thermal and hygrometric conditions, thus increasing operating costs and
environmental impact.
Regarding the constructive characteristics of farm winery buildings, various analyses were
carried out on significant study areas by Tassinari et al. (2011a, 2011b, 2013) and Torreggiani et al. (2011, 2014). These studies have shown that most of the farmsteads have developed by adding more recent buildings beside existing structures, with very heterogeneous
material and formal solutions. For new buildings there is both an explicit research of architectural solutions designed to draw the typical elements of rural traditional, and the use of structures typical of industrial buildings, with poor architectural value and in contrast to the rural
landscape context.
Actions of maintenance or transformation of existing buildings of these farms may represent
an opportunity to enhance the performance of thermal insulation of the building envelope and
thus their energy efficiency, and introduce design solutions and materials compatible with the
typical local architectural features.
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3.
Materials and methods
The research identified the Imola District (Emilia-Romagna, Italy) as an appropriate study
area, due to its significance within the wine sector at the regional level, in terms of potentials
and production (Tassinari et al., 2010). A representative sample of farm wineries, characterized by annual wine production smaller than 5000 hl, was selected (Torreggiani et al, 2014).
A single case study farm was then identified with yearly production capacity of 1500 hl, i.e.
close to the average value found for farm wineries in the study area.
The farmstead under consideration consists of three buildings: a traditional rural two-storey
masonry building which includes spaces for tasting and commercialization, a basement and
an underground cellar for wine aging, with no air conditioning system; a shed used for the
production of wine; and a small single-storey aboveground building for storing bottled wine,
with thermal control systems.
The latter has vertical steel structure, timber roof structure covered with tiles, outside finishes
in wood and inside in plaster. This building has been the subject of a detailed digital modeling for thermal simulations through Energy Plus software, an open-source program for energy analysis and simulation of thermal loads (USDOE, 2013). The software calculates the
heating and cooling loads necessary to maintain thermal control setpoints in buildings, and
the energy consumption of primary plant equipment. In particular, different envelope solutions in terms of wall layers were digitally implemented, and the results of the corresponding
thermal simulations were compared. This allowed to identify efficient design choices from an
energy point of view and to quantify the possible energy saving for temperature control systems.
First, a detailed architectonic survey was carried out aimed at precisely identifying geometric
features, dimensions, building envelope materials, openings, orientation and other data that
affect the variation of internal temperatures and have to be implemented in EnergyPlus modeling environment. Material survey showed the overall composition of the outer envelope of
the structure: a package wall, consisting of 1 cm internal plaster, 15 cm hollow brick, 10 cm
of insulation (expanded polystyrene) and an outer coating 2 cm thick of wood planks; a tiled
roof with insulation of 10 cm; an entrance door consisting of 5 cm of insulation (rock wool),
internally covered by a 2 mm thick steel plate, and externally by wood planks; a floor deck 10
cm thick of lightweight concrete.
The geometric survey outcomes were also used to reconstruct a first digital model, through
the combined use of SketchUp software and the graphical interface Openstudio (NREL,
2012) integrated with Energy Plus (Figure 1). The various elements of the virtual model were
assigned the features of the materials detected, i.e. thickness, roughness, thermal conductivity, density, specific heat.
Outdoor environmental conditions have been monitored by a weather station type PCEFWS20 installed in the proximity of the buildings. It has been recording temperature, moisture, pressure, wind velocity and direction, with a frequency of 30 minutes for a whole year.
Data collected were provided as inputs for simulations. Heat transfer was modeled through
the conduction transfer function (CTF) algorithm, on the basis of the state space method
(Ouyang and Haghighat, 1991).
Four model configuration have been considered, identified according to the following numeration:
1. Actual condition of the building, as it was surveyed;
2. Same condition as configuration 1, with the absence of the layer of 10 cm of insulation. It represents the building configuration existing before the most recent rehabilitation action carried out by the farmer;
3. Building configuration with significant higher level of envelope insulation as configuration 1. This was achieved by considering a 14 cm thick insulation layer.
4. Building envelope consisting in a single masonry layer of 60 cm (a full four bricks
thick), with the same wood cladding and internal plastering as the above models. The
masonry layer represents a typical rural traditional constructive solution. This configuration has been designed particularly to show the effect of masonry thickness and the
resulting thermal inertia of the wall on internal temperature behavior of the building.
The main physical properties of the four wall packages considered are reported in Table 1.
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Table 1: Trasmittance and inertia properties of the wall packages considered.
Configuration
Trasmittance (W m-2 K-1)
Surface Mass Density (kg m-2)
1
0.291
150
2
1.071
148
3
0.226
150.8
4
0.84
988
The time span considered is the whole 2013 year; time step adopted for processing was 15
min, while temperature results have been provided in terms of hourly average values.
Figure 1: Pre-processing software interface and perspective view of the building model.
4.
Results and Discussions
Simulations carried out for configurations 1 and 2 revealed internal temperature trends
shown in Figure 2. In particular, The first simulation showed that, in case plants are turned
off, internal temperature would vary from 2°C in January to about 29.5°C in July-August, thus
calling for the use of cooling systems to maintain the temperature below 20°C, for about four
months, from June to early October. Moreover, the diagrams show that lack of insulation
causes a temperature increase of up to 3.5°C summer and a decrease up to 2.5°C in winter.
In configuration 2, the period of the year when a cooling system is necessary to keep ambient temperature below 20°C is larger, from May to half October. The overall temperature difference from such threshold showed a considerable increase in the case without insulation.
This difference was computed in terms of degree-hours above 20°C, and resulted 13867
degree hours with insulation, versus 19466 degree hours with insulating layers.
Therefore it is clear that the insertion of a 10 cm thick layer of expanded polystyrene in the
outside envelope, produces a significant improvement in terms of energy efficiency.
With configuration 3, in comparison with configuration 1, a modest increase in the maximum
temperature difference was found , amounting to less than 1°C in the second half of June. In
the most critical period, temperature trends nearly overlap, as it is illustrated in Figure 3. The
overall difference from the 20°C threshold is 13248 degree hours, i.e. near to that of configuration 1.
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August
2
1
January
Figure 2: Comparison of hourly mean indoor air temperature variation throughout the year in configuration 1 (blue line) and 2 (black line).
Figure 3: Temperature trends of configuration 1 (blue line), 2 (black line), and 3 (cyan line) in August.
Finally, configuration 4 was analyzed: the results can be summarized by the value of 17502
degree-hours above the 20°C threshold, which means a better performance than configuration 2, but worse than those obtained through the adoption of insulation layers. The effect of
masonry thermal inertia on indoor temperature behavior can be assessed by comparing configuration 2 and 4, as it is shown in Figure 4. The adoption of masonry envelope with high
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thermal inertia resulted in a reduction of peak temperature up to 2°C, and a reduction of daily
temperature oscillation, in comparison with a thin hollow brick layer (configuration 2).
Figure 4: Comparison of temperature trends of configuration 2 (black line) and 4 (blue line) in the
coldest month (January, upper diagram) and in the warmest one (August, lower diagram).
As wine storage calls for temperature values not higher than 20°C, energy demand needed
to keep indoor conditions below such threshold was computed. The results (Table 2) are expressed in terms of thermal energy to be transferred, regardless of HVAC plant efficiency. A
comparison was made with the actual building condition, i.e. configuration 1. Results underline that the adoption of a 10 cm insulation layer lead to energy saving of 55% of current
consumptions. Further saving may be achieved with thicker insulation layers, e.g. 10% is
expected with 14 cm. Increasing thermal inertia of external walls (configuration 4) does not
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appear an effective solution to achieve energy efficiency for the considered microclimate target, as it entails energy consumption 39% higher than configuration 1.
Table 2: Energy demand for air conditioning.
Configuration
Energy demand [GJ]
Relative difference from configuration 1
5.
1
6187
-
2
13644
+55%
3
5648
-10%
4
10184
+39%
Conclusions
The study represents a contribution in the search for best practices for energy modeling of
agro-industrial buildings. The model developed allowed to perform thermal simulations, testing the application of different wall packages (for example, by integrating existing packages
with additional materials), and to assess the respective effectiveness in terms of energy demand. In particular, results provided quantitative indications about thermal performances of
various solution of wall stratigraphy that can be adopted to optimize energy efficiency. This
methodology proved suitable to guide the choice of building materials and technical solutions
in the design of new wine storage buildings, and in the thermal adaptation of existing ones,
identifying the most energy-efficient configurations.
Further developments of the study are expected to consider the integration of obtained results with cost/benefit analyses related to various solutions considered, quantifying the redevelopment cost and the savings deriving from a less intensive use of facilities or - in case of
passive envelope construction - to their complete disposal.
6.
References
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Cosimo Bartoli (The architecture, translated by Cosimo Bartoli), Vol. V, ch. 17, p. 157. Venice, Italy.
Barbaresi, A., Torreggiani, D., Benni, S., & Tassinari, P. (2014). Underground cellar thermal
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Di Giorgio Martini, F. (1967). Trattati di Architettura, Ingegneria e Arte Militare (Treatise on
architecture, engineering, and art of war), Vol. II, p. 337. C. Maltese, ed. Milan, Italy: Il Polifilo.
Marescalchi, C. (1965). Manuale dell’Enologo (Winemaker’s manual). Casale Monferrato,
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Tassinari P., Galassi S., Benni S., Torreggiani D. (2011a). The built environment of farm wineries: an analysis methodology for defining meta-design requirements. Journal of Agricultural Engineering, 2, 25-31.
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