Stuppy Greenhouse Blog

How does heat loss occur?

Heat loss occurs from a greenhouse structure whenever the interior temperature exceeds the exterior temperature. The rate at which it occurs is affected primarily by the efficiency of the covering materials (glazings) installed on each surface (roof, side walls, and end walls). The most commonly used covering materials all have published heat transfer factors called “U” factors that provide a means of calculating their impact on heat loss in different scenarios.

What is the “U” factor?

“U” factors are the inverse of the commonly used “R” factors, where “U” = 1 / “R”. The lower the “U” factor, the less ability your glazing material has to transfer heat, therefore, the lower the heat loss.

This article is brought to you by the NGMA

What are greenhouse curtains?

Greenhouse curtain systems are called shades, screens, and even blankets. No matter what they are called, they consist of moveable panels of fabric or plastic film used to cover and uncover the space enclosed in a greenhouse. Curtains may cover an area as small as a single bench or as large as an acre. Small systems are often moved by hand and large systems commonly by motor drive. Internal shade systems mount to the greenhouse structure below the rigid or film covering of the house. They are used for heat retention, shade (and the cooling effect of shade), and day length control or blackouts when the covering transmits lower than 1% of the incident light.

How do the curtains provide heat retention?

Any interior curtain system can be used for heat retention at night when the heating demand is greatest. Blackout systems can serve this purpose, even when day‐length control is not a consideration. The amount of heat retained and fuel saved varies according to the type of material in the curtain. Curtain systems can save energy in three ways; they trap an insulating layer of air, reduce the volume that must be heated, and when they contain aluminum strips reflect heat back into the house. A curtain system used for heat retention traps cold air between the fabric and the roof. This cold air falls into the space below when the curtain reopens in the morning. To avoid stressing the crop, it is important to uncover the curtain gradually to allow this cold air to mix with the warm air below. Alternatively, if the crop can tolerate the shade, the curtain can be left uncovered until sunlight warms the air above the system.

A grow light is an artificial light source designed to stimulate plant growth by emitting an electromagnetic spectrum appropriate for photosynthesis. Grow lights are used in applications where there is either no naturally occurring light, or where supplemental light is required. For example, in the winter months when the available hours of daylight may be insufficient for the desired plant growth, grow lights are used to extend the amount of time the plants receive light.

Metal Halid (MH)

• Produce an abundance of light in the blue spectrum
• This color of light promotes plant growth and is excellent for green leafy growth and keeping plants compact.
• Best type of light to be used as a primary light source (if no or little natural sunlight is available).
• The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to finally burn out.
• If you compare their lumen (brightness) per unit of energy consumed, metal halides produce up to 125 lumens per watt compared to 39 lumens per watt with standard fluorescent lights and 18 lumens per watt for standard incandescent bulbs.

How do environmental control computers benefit horticulture?

The greenhouse environment must be accurately controlled to produce optimal conditions for crop production. In addition to controlling the humidity and temperature, environmental control computers can manage shade systems and supplemental lighting, control carbon dioxide concentration, schedule and sequence irrigation valves, and control the pH, EC, and temperature of the irrigation water. Because they integrate these functions into a single control system, environmental control computers can manage the complex instructions between these elements providing the grower with a tool to optimize production.

This article is brought to you by the NGMA

CO2 Concentration and Plants

Photosynthesis is the process of plants using light energy to convert absorbed carbon dioxide (CO2) and water into sugars. Plants use these sugars for growth through the process of respiration.

Plants absorb CO2 through their stomatal openings located mainly on the underside of leaves. Although light, moisture, temperature and humidity levels all affect the rate of CO2 absorption, the concentration of CO2 outside the leaves is a significant influence.

The concentration of CO2 in ambient outside air commonly varies from 300 to 500 parts per million (ppm) or more by volume depending on the season, time of day and the proximity of CO2 producers such as combustion or composting, or CO2 absorbers such as plants or bodies of water. Plants growing in greenhouses, particularly “tight” double‐layer structures with a reduced air infiltration rate, can reduce CO2 levels to well below ambient levels, greatly reducing the rate of photosynthesis. Conversely, enriching the concentration of CO2 above ambient levels will significantly increase the rate of photosynthesis. In general, a drop in CO2 levels below ambient has a stronger negative effect on plant growth than the positive effects of enriching CO2 levels above ambient.

This Article is brought to you by NGMA 

Daily CO2 levels in un‐enriched greenhouse environments will climb to several hundred ppm above outdoor ambient at night due to CO2 produced by plant and microbial respiration. CO2 levels drop quite rapidly after sunrise as the crop’s photosynthetically‐driven consumption of CO2 exceeds the basic rate of respiration. In the absence of some other source, CO2 levels remain low all day limiting plant growth. At dusk, plant and microbial respiration once again begins to accumulate CO2 in the greenhouse.

These are objectives to investigate and complete as you work towards getting your greenhouse up and running.