KEEPING A GREENHOUSE COOL (ON A BUDGET)
by Adrian White
20 December, 2021 by
KEEPING A GREENHOUSE COOL (ON A BUDGET)
Lucija Johum

It’s a known fact that greenhouses are designed to raise temperature. With a translucent glass or plastic cover, the sun’s rays are able to reach the soil surface underneath, where heat is absorbed. This heat then radiates back upward but becomes trapped within the covered structure, creating a warmer microclimate for your plants.

On sunny but cold days, this natural mechanism is a godsend for plants that need it. The difference of a few degrees allows you to grow things that you otherwise wouldn’t have been able to without investing in a greenhouse. On sunny, hot days however, this temperature boost becomes a whole other matter altogether.

Every greenhouse needs a way to moderate temperature. On a very sunny day, temperatures within your setup may jump even as much as 20 to 30 degrees higher than air temperatures outside. On a calm 70° F day, temperatures in your structure can quite possibly rise to 100° F or more.

Those with wealth, highly lucrative businesses, or plenty of capital to cover cooling costs can, of course, use air conditioning, electric temperature regulation, or other costly methods to keep their operation cool. But what about the price and environmental impacts? What options do thrifty DIY growers and humbler operations have? 

The good news: there’s plenty. Whether you’re dealing with hot climes or the height of summer, make sure you have some sort of method (or methods) on hand to keep your setup cool and avoid overheating – for the sake of your plants, your hobby, and/or your business.

KEEP IT CHEAP

Frugal greenhouse growers of all kinds have developed the following tricks, approaches, and accessories over time to keep things cool. For your own benefit, you can take them as your own, too.

ROLL-UP SIDES

Almost every greenhouse model comes with some type of roll-up side: whether it’s a hoop house, gothic arch, or other model. If your setup doesn’t come with any other cooling accessories, it’s very wise to at least consider a kit with roll-up sides built in, as you’re going to need at least one way to release some of that trapped heat outside. 

As a passive ventilation cooling system, being able to vent the sides of your structure comes at no additional cost and is quite effective. The most basic kits with roll-up sides will likely have a channel and wiggle wire attachment system that allows you to attach and re-attach plastic to either baseboards or greenhouse ribs to open and close. 

A step up from that may be manual or automatic roll-up sides. Either crank your greenhouse sides open effortlessly by hand, or tie it into an automatic or timed system that you operate remotely – or at the touch of a button.

PASSIVE COOLING WITH DOORS

In addition to (or apart from) roll-up sides, even the simplest, un-accessorized hoop house or other structure can be vented by virtue of its most basic design elements: doorways. Growers can simply open doors to their structures on especially hot days, which is a huge help in and of itself. 

With this tip in mind, it’s recommended that greenhouse owners take interest in models with doors at both ends of their structure, which helps with the best airflow. When using doorways to vent, you can also use the advantages of wind direction on windy days as a natural “fan” through your system – especially when the wind is coming straight out of the west.

SHADE CLOTH

You can’t overlook the obvious method for cooling down any space: casting shade. If you invest in shade cloth coverings – typically a netted black material – these can be easily placed over smaller greenhouses during certain times of day to provide shade, thus cooling down your operation. While they tend to be black material, some reflective white coverings help cast shade and deflect light and heat, too.

The good news: shade cloth is quite affordable, and can be used again and again year after year. For larger greenhouses, there are even larger automatic shade systems you can set timers to for scheduled coverings and uncoverings throughout the day if it happens to be a hot one – though this is pricier to invest in.

SMART LANDSCAPING

If you think about it, the way you landscape or plant around your greenhouse may impact how hot or cool it gets in the summer. More specifically: if you plant certain trees in specific, strategic spots, they can actually be of benefit with the shade they cast on your structure during the latter part of the day.

Thinking about planting some tall (or potentially tall) trees near your growing structure? Consider planting them on the south or southwest side, especially if they are a variety that will only cast dappled shade (avoid heavy shading trees such as evergreens). This way your greenhouse receives some relief in the afternoon, that is if the plants in your setup will are the type that could really use it during hot weather.

COOLING PADS

Evaporative cooling pads are a new, passive, and quite genius technology for lowering greenhouse temperatures. Using corrugated, environmentally-friendly paper material, these pads absorb cold water, which then pull hot air through gaps at one end of the structure and out the other. This air is rendered cold, then evaporated into the greenhouse air environment in the form of cool humidity.

Many of these pads are available on the market and are quite affordable. Though they may need to be changed or replaced every year or every so often (depending on the quality), beyond their passive cooling function, there is practically no additional costs to making them work – save for the costs of running water into the pad.

WATER WALLS

Similar to evaporative cooling pads, water walls utilize air currents through a cool water fixture in order to generate cool air currents within a space. Typically, the actual water wall is placed at one end of the greenhouse, and fans on the other. Other openings like vents, windows, and doors must be closed in order to boost the maximum amount of airflow only through the water wall, and to then create the coolest air drafts possible.

Actual constructed models of water walls tend to vary. But all in all, adopting one into your system – much like a cooling pad – is quite cheap and affordable, only including the reasonable costs of buying the equipment (or making the setup) and the price for running water.

NO BUDGET CONSTRAINTS, NO FEAR

If you’ve got the dough to throw around, look into some of these options to make sure your greenhouse can beat the heat, so to speak.

VENTILATION

Take ventilation a step farther than roll-up sides, and invest in an actual sophisticated ventilation system (though you can always invest in both). The strategic installment and placement of vents further assists with the passage of overheated air out of your structure to allow cooler temperature air inside, all while bringing temperatures in your greenhouse back into balance.

Better yet, combine a ventilation setup with an HVAC control system, and you can change your ventilation from passive to active for quicker cooling. Both ventilation and controls will be an investment at first, and not the thriftiest of options (though if you are not building them in as part of an intake or exhaust component, vents alone will be more affordable). But if you can swing the costs, it’s a very worthwhile investment to make for the protection and well-being of your plants.

FANS

Fans are a generally affordable addition to your greenhouse, as they can help reduce heat pressure – though some fans are more expensive than others. Combine them with an active or passive ventilation system (even a water wall or cooling pad to help diffuse cool air) and this even further assists with the balancing of temperature in your greenhouse, helping you meet the ideal environment standards for your crop. On top of their ability to help with cooling, fans can also ensure that air quality is TOP quality in your growing space. 

Plus, the movement of air has some desirable impacts on reducing moisture, which can then keep down disease – as well as improve stem strength on spindly plants like flowers, tomatoes, vines, and more. Combine them with vents or a ventilation system, and you have yourself a cooling match made in heaven.

RADIANT EARTH COOLING

This method is quite an expensive one to invest in up-front. But once you do, you have quite a large and successful passive cooling system that will benefit you for years and years to come at practically no additional cost; though make sure you do it right, as repairs can be frustrating and costly.

Radiant earth cooling involves the installation of subterranean pipes under a greenhouse, which then carry water of various temperatures that emit those temperatures into the greenhouse through passive heating or cooling. As stated above, installation of these pipes is the most expensive part, and then there are the water costs (especially in the case of heating water for warming your structure). On the other hand, cooling a greenhouse with this method would be less costly than heating it.

COOL OFF YOUR CROP

Greenhouses of every size – whether large or small, hoop houses or gothic arch shapes – need a cooling system for those times when temperatures climb just a little too high. Keep the tips and accessories from this article in mind for the coming season, so your plants stay in tip-top shape; but most importantly, so you can keep on growing great products unimpeded!

KEEPING A GREENHOUSE COOL (ON A BUDGET)
Lucija Johum 20 December, 2021
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