Greenhouse Design Options 15

The crop grown and purpose of a greenhouse both affect its structure, its technological requirements, and its construction components. Depending on the choices the hapū select, the greenhouse can feature several different design options. Of particular interest are hydroponics, aquanponics, and the possibility for a trial greenhouse.

2.8.1  PlentyFlora  

PlentyFlora is a glasshouse located five minutes from the Ngāti Kea Ngāti Tuara Hapū. PlentyFlora heats their greenhouse using geothermal energy from two geothermal bores. They drilled a new bore two years ago, which produces 65°C geothermal fluid. PlentyFlora uses this directly in the greenhouse, mainly for air heating in an overhead system. The system injects the cooled geothermal water back into the shallow geothermal reservoir. A bio diesel peak heating system on a fan coil gives the plants hot air when needed (Lind, Bradshaw & Bell, 2015).

2.8.2  Materials  for  Construction  

The team considered three candidate materials for the construction of the proposed greenhouse. Glass is the most expensive option, depicted in Figure 16, and can cost hundreds of thousands of dollars. It is also the most durable option, lasting 40-50 years. Advantages include that glass is non-combustible, resistant to UV radiation and air pollutant degradation, and would be relatively easy

conditions can easily damage the glass. Rotorua has a temperate climate and lies off of the fault line that runs through New Zealand, lessening the concerns surrounding weather and earthquakes.

Polyethylene film, shown in Figure 17, is the cheapest option, and costs just a fraction of the glass option in the thousands of dollar range. It is the simplest form of covering and is very flexible. However, this option does not come without its downfalls, most notably life expectancy. Photochemical degradation processes in all plastics from ultraviolet radiation, air pollutants, and chemicals from pest control all result in plastic’s life expectancy of only 3-5 years.

Rigid panels fall under the category of polyethylene material. This option, displayed in Figure 18, is more expensive than the film but has a life expectancy of 10-15 years and is easier to maintain. Greenhouse designers can space the panels wider apart, creating less shade on the crops than glass. The downside of this option is that it has low air infiltration. This improves energy savings but contributes to humidity, which affects crop production (Giacomelli, 2001).

2.8.3  Ground  and  Water  Considerations  

In order for construction to take place at Ngāti Kea Ngāti Taura, the land must be well-drained, level, of good water quality, and have access to roads for materials and products. Figure 19 shows part of the plot of land. From our initial observation and conversations, the plot seems to fit these parameters. The bulldozed section currently measures 25 by 50 meters and has the potential to expand. As of late January, 2016 it has a number of potted plants. It is also important to note that a healthy water supply is an essential component for the greenhouse. A water quality test determines the water’s pH, hardness, salinity, and dissolved minerals.

Figure 17: Thin Film Greenhouse (American Society of Agricultural and Biological Engineers)

Figure 18: Rigid Panel Greenhouse (The Big Greenhouse Project, 2007)

There are other elements of physical structure the team considered. One type of growing system, called ground-to-ground or Quonset, is initially cheaper. This option’s biggest limitation is space. On the other hand, a gutter-connected structure presents an alternative option and allows the hapū to expand the structure in the future. This design can share environmental control systems and other equipment, including heating, cooling, and irrigation. The downside is that there is no isolation for disease or pest control.

2.8.4  Trial  Greenhouse  Possibilities  

A trial greenhouse is a possible solution if the hapū does not feel the economy is stable enough for a more permanent structure, or if the initial expenses

related to building and maintaining a greenhouse are too high for the hapū to absorb. A small-scale trial hydroponic system, shown in Figure 20, is a good first step. This allows the hapū to gauge necessary nutrient inputs, growing speeds and taste.

A trial greenhouse, such as a hoop house as seen in Figure 21 is a non-permanent solution and much cheaper alternative. Mobile hoops allow for the better use of cover

crops and crop rotation, while increasing crop production. A full-time hoop house farmer could fit about ten hoop houses onto one acre and earn about $25,000 a year. The downside to a hoop house is that it has no ventilation fans or heater, harming plant growth. This also means that the hapū would need someone to open it every morning and close it every afternoon. A solution to this is removing the plastic skin and then covering half of the hoop house with shade cloth. Builders can install sprinklers on the ground or attach them to the top of the hoop house for cooling and irrigation (DeVault, 2003).

Figure 21: Homemade Hydroponic Trial Tub (plantozoid.com, 2015)