Cow Barns - Reduce feed wastage, improve efficiency...

The REL Wintering Barn Design is protected by Copyright and MUST NOT be copied without first obtaining the written permission of Rakaia Engineering Limited.

Ventilation Info

Introduction

Introducing REL's new Controlled Environment Stock Sheds.

This new innovative elliptical curved controlled environment free stall shed has been engineered to ensure a high level of thermal buoyancy and ventilation performance, increased stock health and performance and a more visually aesthetic structure to fit in with New Zealand's typical rolling rural surroundings.

REL and Kirk Roberts Consulting Engineers Ltd. have combined their knowledge in the agricultural and engineering sectors to design a more efficient and environmentally effective solution to intensive / wintering stock farming.

Wintering / housing sheds reduce the environmental and active energy demand for dairy cows (or other stock) by removing the restraints of the environment and stock load on pastures. This allows cows to have  higher productivity due to increased feed conversion efficiency, controlled feed and supplements, less feed wastage and the ability to increase stock pile, stock health, limiting soil and pasture damage, and removing adverse weather stress in the stock. Pasture grazed cows cannot reach or maintain the same levels of milk production as cows housed in controlled environments.

At present the New Zealand building and agricultural industries have no standards for this type of structure and the industry is making the same mistakes overseas countries made, with major repercussions such as poor stock health and low production, poorly ventilated environments with issues such as condensation, overheating, and stale air. REL are leading the market by investing in research and development to design better and more advanced Controlled Environment Stock Sheds, ahead of legislation and council restrictions, to ensure the capital costs invested in these structures are a secure longer term investment.

We have carried out extensive research and calculations based on agricultural and thermal modelling research papers from northern hemisphere universities and current European standards to ensure these sheds have a more than adequate environment for stock by way of increased thermal buoyancy and ventilation performance. We have carried out extensive design and research in developing the elliptical truss which is the most efficient large span structural system. We have implemented the stock health recommendations from Dairy Production Systems Ltd. (Sue Macky), by way of addressing ventilation flow, increasing cubicle widths, adding runoffs and nursery areas, larger lane and aisle widths and using specialist European made matting and plastic cubicle dividers.

Aesthetics and Structural Performance

The elliptical curved frame is a very sleek architectural structure with clean curved lines typically used in stadiums for its structural efficiency and its elegant appearance. The curved sheds allow for a lower apparent aspect ratio which hides the buildings large height for increased ventilation control and allows the curved structure to visually blend in to New Zealand's rolling country side.

The elliptical curved shed performs significantly better than typical sheds currently being built in New Zealand. The typical sheds used and built at present in New Zealand are performing extremely poorly in all aspects including structural efficiency, aesthetics, stock health, the environment, future proofing, shed ventilation and air flow.

The elliptic curved shed form is a structurally efficient structure which allows the building to have large knee heights, increased roof pitches, increased apex heights, cross sectional volumes, large clear spans with reduced construction and material costs. The elliptical curve allows the shed knee (side walls) to be high with minimal impact in cost, the curve gradient starts off steep at the side walls at around 32° to the horizontal through to around 4° at the central feed way. The increased pitch at the sides allows the shed to rise rapidly on its outside third resulting in larger air volume above stock, compared with conventional sheds.

The arch resists vertical load by axial compression along the truss cords allowing the use of slender members maximising their strength thus creating an economic and robust structural system. Conventional sheds with typical portal frame construction resist loads by pure bending which is a much less efficient way to support load. Lateral loads resisted by the curved truss are connected directly to the ground via an axial connection thus additional truss height, span or weight does not effect its ability to resist high wind or seismic loads. This means the structure has redundant lateral capacity allowing it with perform better in extreme load events. Hence typical portal frames are inefficient structures in comparison and would require significantly more structure to resist earthquake and wind effects than the equivalent curved structure.

Due to the curve and truss nature of the shed, large eaves are achievable on the side walls to ensure the side stock bays are protected from prevailing wind and rain without any consequence to the ventilation.

The average height of the shed above the stock is approx 6.0 meters ranging from 4.0 m at the sides, to 8.20 m at the side of the feed way to 9.5 m at the apex. To achieve the same amount of volume and knee height a conventional shed would require a 19° roof pitch with a, 10.0 m apex (10.5 m including rafters). To achieve this level of performance in a typical portal frame shed the building would require significantly more structure to resist earthquake and wind effects.

The elliptical curved shed allows efficient air flow over the building with minimal turbulent air pressures at the inlet and outlet openings.
In conventional sheds air flow becomes less efficient and creates more turbulent pressure loads on the building and less stable air pressure at the
inlet openings in comparison to the curved structure which allows air to flow over the structure efficiently with minimal turbulence.

Ventilation and Thermal Buoyancy

INTRODUCTION

Kirk Roberts Consulting Engineers Ltd has been engaged by REL ,to carry out research and analysis of natural ventilation through thermal buoyancy and wind on wintering barns. This report is focused on a curved wintering barn and the basis of this report and modelling will be extended to assess the performance of alternative designs in REL's portfolio. This is to ensure the viability, longevity and high performance of naturally ventilated stock barns and to ensure that the sheds have adequate ventilation to ensure a high level of stock health.

SUMMARY

The curved shed performs significantly better than typical sheds as they are currently being designed. Its benefits include:

• High Mass Discharge, large knee heights and inlet openings.

• Shed ventilation and mass discharge is very stable and stabilises quicker with fluctuating temperatures and wind speeds.

• Large sectional air volume and increased air replacement for stock.

• Increases performance in adverse climates when Vv=0m/s (zero wind), and the shed is ventilating with thermal buoyancy only.

• High apex height, allowing good thermal buoyancy air flow.

• High knee height to allow adequate inlet air flow and head height in side stalls and large eaves to remove prevailing weather from effecting stock with out the need for side walls.

• Increased roof pitch and head height in the critical areas (side bays).

• Structurally efficient building resulting in decreased construction costs and the ability to achieve large clear spans.

In summary, based on calculations and research, the curved elliptical shed outlined in the report performs significantly better than current designs and has specific attributes proving that it is fit for purpose.

COMPARISON RESULTS - REL CURVED SHED VS CONVENTIONAL DESIGNS

The philosophy behind this analysis is to compare REL's curved shed against a conventional NZ style wintering shed which is currently being built or has been built in a number of locations in the lower south Island. The REL shed has been designed with considerations and recommendations for knee heights, apex heights, cross-sectional volumes, inlet and outlet opening sizes from northern hemisphere publications.

SHED 1 - typical New Zealand shed:	SHED 2 - REL curved shed
2.7 m knee (iron roof)	3.93 m knee (iron roof)
6.25 m high apex	8.40 m high apex
12.5° deg pitch	32.8° at eave to 3.92° deg at outlet vent
32 m wide x 100 m long	32 m wide x 100 m long

The graph below looks at an extreme condition with a wind speed of 0 m/s and a temperature differential of 7.5°C. This case outlines the performance of the shed under thermal buoyancy conditions only, without any wind effect and a reasonable temperature differential.

Mass air flow rate for the curved shed has increased by 152%, with the air flow speed increase of 26%. Also the air replacement per stock is greater by 152%. This outlines that once the wind is removed (worst case situation) and there is only thermal buoyancy to ventilate the shed the percentage between the performances of the two sheds increases further. This shows the curved shed performance increases in high risk situations (no wind) and is a more stable environment.

We have also plotted the mass discharge of Shed 1 (typical shed) against Shed 2 (Curved shed) in the graph below, plotting the discharge rates with Vv=0m/s (zero wind) against fluctuating temperature changes within the shed (Thermal Buoyancy effects only).

The above graph shows that Shed 2 (curved shed), out performs Shed 1 for the entire range of temperature differentials. Also note that Shed 2's curve increases more rapidly meaning that with increased or rapid changes in temperatures the shed can react and stabilize the internal environment faster than the conventional shed by being able to re-circulate air faster through thermal buoyancy effects.