Cooling a Greenhouse without Electricity
You want a greenhouse. You know it will build up a lot of heat during the day. Even on sunny days in the middle of the winter. You want to put it by your garden in a remote corner of your lot. Or maybe, on some land that you own that is undeveloped. What do you do? Fortunately, there are multiple options for cooling your greenhouse even when you don’t have electricity. Let’s take a look at the options.
This one is a no brainer. Just install a shade cloth over the top of your greenhouse. It has much the same effect as standing under a shade tree in the summer. The shaded area will be cooler. Shade cloths are available in a woven, knitted or reflective material. The woven material will ravel when cut and it is necessary to put tape on the edges. Knitted shade cloth has more give than the woven and does not require taping, although we prefer to do this as you can then put grommets in the tape. You can run a bungee or cord through the grommets to attach the cover to your greenhouse. There is also a reflective cloth available which is much more efficient. They result in lower greenhouse temperatures and a more consistent environment. Shade percentages run from 50% to 70% for greenhouse use, maybe lower for plants will low light requirements.
2) Roof vents –
Chances are if you are purchasing a greenhouse kit, it will have roof vents. There are very few kits out there without roof vents, and if you are building your own greenhouse, this is a highly desirable feature. We all learned in high school that warm air rises. Have an opening such as the roof vent in the top of your greenhouse, and the hot air will exit. Manual roof vents are available, but the best way to take advantage of this feature is to have a solar powered opener on it. That way if you are not at the greenhouse every day, you will know that the vents are opening and closing at appropriate times. These solar powered openers are basically wax cylinders. They work on the principle of contraction and expansion. When they get warm they expand, pushing the vents open. When they get cool they contract, pulling the vents shut. These can be adjusted to a certain degree to open and shut at desired temperatures.
There are also roof vents available that will go directly into a polyfilm greenhouse without additional framing. They have the solar powered openers. These vents can be retrofitted onsite to fit in a polycarbonate greenhouse.
3) Side vents in conjunction with roof vents –
If you place a side vent with a solar powered opener below your roof vents you will get even better ventilation in your greenhouse. We like to place these approximately 6″ from the bottom of the greenhouse. This will give you a chimney type effect drawing the air from the bottom to the top of the greenhouse. We also use the wax cylinders on these to keep things simple.
If you have a greenhouse with straight side walls you can install roll up curtains. Using these you can roll the greenhouse sides up during the hottest times of the year. These systems operate with a hand crank or can be automated. These come with a heavy duty 12 mil coated weave fabric. It is recommended to use a kneewall with these systems. That way your plants will have protection from the wind when the curtains are open. Also, if you are in a heavy snow area, this will keep the snow from laying up against your curtain.
These operate on the same principle as a wired ventilation package. But, they are powered by a solar panel. The exhaust fan goes up high in the backwall of the greenhouse. The intake shutter(s) go down low on the opposite wall. The exhaust fans are wired to a thermostat. The manual intake shutters will open to allow fresh air into the greenhouse. The exhaust fan will draw this air through the greenhouse, cooling the air. No electricity is required, you are creating your own power.
Circulation fans are essential to the healthy greenhouse. They will increase CO2 availability, an essential for plant growth. They help to reduce excessive moisture creating an environment which reduces disease and pests caused by humid environments. They also help strengthen the plant stems with the same motion as a mild breeze when the plants are grown outside. These are fans that run low and slow.
7) Misting Systems –
Misting systems may be used if you have water to your location. They will help to lower the heat in a greenhouse. These can be set up on a battery operated timer, so no electricity required. These cause a cooling effect by tiny water droplets evaporating.
I have been fighting an uphill battle at times throughout the years. New greenhouse owners just do not understand the heat that will build up in a greenhouse during sunny days, even in the middle of winter. I have seen my ventilation package come on during a sunny 60 degree February day. And, I keep my thermostat set at 90 degrees. Quite a difference that you really would not expect unless you have experienced it. Proper ventilation is an essential item for your greenhouse. It will keep your plants healthy and happy. No more baked tomatoes on the vine. You will have to pick them and put them under the broiler in the kitchen for that! These options discussed above provide you with the opportunity to supply adequate ventilation to your greenhouse even when they are in an area with no power available. So, no more excuses. Get out there and build yourself a greenhouse today. I will also be discussing heating your greenhouse without electricity when the season dictates. Good Growing!