APPLICATION OF LIFE CYCLE ASSESSMENT TO CONSTRUCTION

MATERIALS: A CASE STUDY OF FARM BUILDINGS

Rajat Nag and Nicholas M Holden

UCD School of Biosystems and Food Engineering, University College Dublin, Belfield, Dublin 4,

Ireland

Abstract

The materials used to construct farm buildings cause impacts to the environment. In this study a

numerical model of a farm building was developed to calculate the bill of materials required for Life

Cycle Assessment (LCA). LCA is widely used to evaluate emissions and consumptions and to find

out hotspots, yet many livestock system LCAs make a starting ‘exclusion assumption’ of not

including farm buildings. Few studies have evaluated this assumption. The influence of seasonal

changes, type of building material (steel and timber) is presented. This approach during the design

stage of a building will ensure compliance with the legislation and is the first step towards a net zero

building concept compatible with the exclusion assumption.

Introduction

According to the Department of Agriculture, Food and the Marine (DAFM) the agriculture and food

sector in Ireland contributes about €24 billion to the national economy and a farm building represent

about 30 to 45 % of the overall project cost for farm development. Worldwide, more than 40% of all

energy use is linked to buildings and they produce one third of greenhouse gas emissions during their

entire life cycle (Koesling et al. 2015). Despite this, many LCA studies of livestock systems omit farm

buildings from the system. The methodology of the overall study was based inter-linking IPPC

legislation, numerical modelling, thermal transmittance and model validation and finally the

application of LCA to quantity impacts (emissions and energy consumption). This paper focuses on

numerical modelling of the farm building.

A numerical model is a description of a system using mathematical concepts and language. Here

numerical models are used because the model may help to explain a system, to study the effects of

different components and to make predictions about behaviour. Experimentation with real farm

buildings is very costly and time-consuming. A numerical model can be used to quantify each of the

major materials to be used in construction of the building. Impact on heating and cooling, durability,

type of animal and the distance from the source to the construction site have a major influence when

selecting a specific type of building material. For example, timber is a good thermal insulator. Hence

during winter, we need to provide less amounts of heat inside the building compared to a building

made of metal and concrete. At the same time durability may be a concern for choice of materials,

because they all do not have a same life span when in contact with urine and faeces, containing the

aggressive ions Cl-, SO42-, Mg2+, NH4

+ with high concentration of H2S, CO2 and NH3 (De Belie et al.

2000b). Monahan and Powell (2011) provided a system diagram for construction materials: Extraction

of raw material or recycled material > Transportation > Manufacturing of components and products >

Transportation to site > Construction > Occupation > Maintenance and renovation > Deconstruction >

Removal from site (Transport) > Disposal. LCA is a tool that can be used for assessing the global

emissions for the materials used in the building. Some material choices are made due to technology,

economy and purpose limitations such as concrete for slated floors in a farm building for cattle (De

Belie et al. 2000a). On the other hand, roof material can be flexible as it may be corrugated GI sheet,

glass fibre or wooden. This study considers IPPC legislations and the flexible areas for a material

choice.

The objective of this study was to model a farm building based on farm building legislation in

order to quantify the bill of materials and to select an equation for heating as well as cooling

which are key inputs for the subsequent LCA study.

Materials and Methods

IPPC legislation and dimensions

A simple steel frame (Figure 1) was assumed. This consisted of a framework of steel stanchions,

rafters, and bracing. It is used for most animal houses with feeding passages, and also for sloped-roof

‘single-sided’ houses. It can easily accommodate feed barriers, pens, and facilitate good ventilation,

and is therefore recommended for slatted or scraped floor houses for cattle, cows or sheep.

Bay

Width

Purlin

Slats

Sheeting

Rail

Ventilated Side

Cladding - 1.5m depth Roof

Pitch

Gap

Outside

Agitation Point

in Slab

SPAN

Stanchions

Overhang

Spaced

Sheeting

Angle

Braces

Ventilation

Outlet

Eaves

Height

Rafters

Roof

Cross

Bracing

Ventilation

Inlet

Figure 1: Single-sided simple steel frame (4 bay) house published by DAFM – S. 101: “Minimum

specifications for the structure of Agricultural Buildings”

This study focuses on rafters and purlins, columns / stanchions, roof sheeting, claddings, sliding

doors. Other components like foundations, mats, concrete floors, slurry tank, concrete apron, external

walls, cubicles & cubic beds, path, metal trough, feeding barriers, automatic scrapers, water trough

are not considered as they are common for scenarios whether steel or timber. The steel structure was

designed in accordance with IS EN 1993 and expected to serve 30 years with a steel corrosion rate of

200 µm thickness loss per year (De Belie et al. 2000c). Whereas for timber-design IS 444 was

adopted. All timber should have a minimum service life of 20 years (mostly pine or cedar) to satisfy

hazard class 4 requirements, as defined in IS EN 335-1:1992. Hence the LCA comparison requires 2

steel buildings and 3 wooden building to provide 60 years of service.

Table 1. Some features of the building according to legislation S. 101. (S) for steel, (T) for timber

Eve height 4m Roof slope 15 degrees

Bay width 4.8m (max for timber) Max purlin spacing 1.12 m

Cladding & roof (S) 0.5mm GI

(T) 12mm ply. (with PVC)

Sliding door (S) 1mm steel

(T) 12mm

plywood

Angle brace

(>1.5m length)

(S) UA 60x60x6

(T) 75x175

Over hanging rafter and

supporting member

(S) IPE 180

(T) 75x175

Stanchions

External column

Internal column

(S) UB 203x102x23

(T) 150x225 (10 nos.)

(T) 75x150 (10 nos.)

Main purlin (S) UA 50x50x6

(T) 50x75

Cross bracing and

main rafter

(S) UA 50x50x6

(T) 75x175

Supporting purlin (S) UA 25x25x3

(T) 50x75

Numerical modelling to quantify the bill of materials

The main elements of a numerical model are in the sequence of observation of the physical system >

numerical model > simulation > prediction. Using finite element methods, the model was split into n

(number of) nodes each with relevant properties. Modelling software (STAAD pro) was used to solve

differential equations to maintain equilibrium condition for each differential sub system.

Figure 2. Numerical model of the farm building: dimensioning and 3D view

Thermal transmittance and model validation

Mass balance of relative humidity, CO2 and heat balance can be estimated using equations:

mi = (1.5 * Wa) / (Wi - Wo) (1)

mii = CO2a / (CO2i - CO2o) (2)

S = [(A * U + Mmin * C) * ∆T] - Hs (3)

Mmax = (Hs - A * U) * ∆T) / (C * ∆T) (4)

As a rule of thumb, Mmax should be limited to ten times of Mmin, CIGR (2002). All the abbreviations

are explained in Figure 3. Further work will validate the model and find ‘U’ for real conditions. With

a set of known data ‘U’ an unknown scenario can then be assessed. Furthermore, depending on the

supplement heating and maximum air flow rate the energy consumption can be calculated for

comparison in the LCA stage of the work.

Figure 3. Model for mass balance of HVAC system in an animal farm

Life Cycle Assessment

After quantification of materials, LCA models for both the scenarios will be built. The functional unit

of the study requires further consideration, but could be: per m2 of building, per m3 of building or per

animal housed, assuming a building 19m x 4.8m x 4.6m providing animal shelter.

mi

Ventilation rate based on relative humidity

Wom

iiVentilation rate to control CO2

CO2o Hot air Wi Absolute humidity of inside air

Wo Absolute humidity of outside air

Wi Wa Moisture production rate by animals

Cold air CO2i CO2i CO2 content of inside air

CO2o CO2 content of outside air

S CO2a CO2 produced by animals

Animal Wa MminMinimum ventilation rate , minimum of m

i and m

ii.

CO2a Mmax Maximum air flow rate to prevent heat stress in summer

Hs Hs Sensible heat from animals

A Area of building fabric

Animal farm building U Thermal transmittance

HVAC Heating Ventilation and Air Conditioning C Specific heat capacity of air

S Supplementary heat during winter ∆T Temperature difference (inside - outside)

Results and Discussion

The numerical analysis with STAAD pro indicated the major quantities for each structure (Table 2).

Table 2: Final quantity of materials obtained from numerical model

Scenarios Major component Quantity (ton) Remarks

Steel Structure Structural steel 2.665 LCA to be performed for

these materials in

accordance with the energy

required to produce

supplementary heat

GI sheet 1.203

Timber Structure Timber frame 2.429

12mm Plywood 1.403

Limitations and future work

The gusset plate quantity and nuts-bolts were not considered. Also, the architectural aspects (Fuentes

2010) of farm buildings were not considered in the initial stage of the study. A survey of farms in

Ireland will be undertaken to collect data for stepwise validation with SPSS statistical software. A set

of random variables that could influence ‘U’ will be defined for the analysis and the regression will be

used to eliminate variables and to establish a co-relation between the input variables and the

dependant variable, ‘U’. LCA for the two scenarios will be used to assess environmental impact.

Conclusions

This study successfully calculated the quantities for the bill of materials of the flexible portion of a

standard farm building for animal housing. This is the first step required to model the thermal

properties and to use LCA for comparing buidling materials from an environmetnal perspecticve. This

will provide a basis for eliminating materials prior to further design steps. This analysis will be the

first step towards the optimization of energy for a net zero building concept. Estimation of total

carbon balance may be possible after completion of an analysis with LCA.

References

CIGR (2002) Climatization of Animal Houses, Heat and moisture production at animal and house

levels. DK-8700 Horsens, Denmark: International Commission of Agricultural Engineering,

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De Belie, N., Lenehan, J. J., Braam, C. R., Svennerstedt, B., Richardson, M. and Sonck, B. (2000a)

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