Out-of-the-Box Cooling Solutions for Your Summer Garden

Summer brings with it so many wonderful things—lake and beach time, fireworks and barbecues, sunshine and of course…heat. Summer can present quite a challenge for most indoor gardeners, as skyrocketing outdoor temperatures affect temperatures in the garden significantly.

Recently, we discussed all of the sources of heat in your garden—one of them being the temperature outdoors—and the ways of accounting for them when you choose a cooling solution. In another issue we’ll talk about total, ground-up, year-round solutions for entire cooling and climate control systems for your garden.

Right now, however, our focus is on short-term help for those gardeners whose cooling systems work well enough for most of the year, but who might need some help during the hot summer months.

We’re going to focus on inexpensive and creative solutions for gardeners experiencing seasonal cooling difficulties. No one likes to shut down their garden for any reason, but unfortunately many of us are forced to scale back during the hotter months—luckily, there are short-term solutions out there!

First, you need to consider every source of heat in your garden when you’re trying to address temperature control. Removing heat sources is always going to be your most cost-effective solution, so think about the equipment that is in your garden now that could be moved outside.

We know that ballasts are a big contributor, but external pumps can add a lot of heat to a growroom as well. Any heat-generating equipment that can be moved should be moved—small changes can sometimes make all the difference when your heat problems are minor and seasonal.

One very helpful and inexpensive solution is the radiant barrier, a heat-blocking cover available from most major reflector manufacturers for their air cooled hoods. They’re marketed under different brand names—depending on which reflectors you have—but they are pretty much the same when it comes to construction, featuring an insulating inner layer with a radiant barrier outer layer.

Air cooling your reflectors is a lot more effective in cooler weather because the outside air passing through them is cool—and as long as the air passing through the reflectors is cool, the amount of radiant heat escaping from them is minimized.

However, if the air passing through your reflectors is hotter than the desired garden temperature, a significant amount of heat is still going to radiate out of the reflector and into the garden.

These radiant barriers do an excellent job of keeping radiant heat from escaping into the growroom, boosting the efficiency of air cooling dramatically—they will actually boost air-cooling efficiency year-round, but the difference is most notable in the summer months when the air is warmer.

Infrared images of reflectors without the covers are typically in the range of 120° F after a 1,000 watt bulb has been burning for a couple of hours. Once the covers are installed, though, the infrared image of the same reflector will show it to be room temperature. This amounts to a major reduction in heat—in my experience, overall cooling needs can drop by seven to 10 per cent when these covers are in use.

Read also:

• Handheld Infrared Thermometers and Imagers in the Growroom
• 5 Ways to Control Odors in a Growroom
• Don't Let 'em Fry! - Managing Excessive Heat

Other excellent solutions for summer cooling are the ducted water-to-air heat exchangers available at most hydroponics stores. These are available in both six and eight inch ducting sizes (when used optimally, the six inch version is capable of removing 5,500 BTU of heat—approximately half a ton—and the eight inch version is capable of removing 8,000 BTU, or approximately two thirds of a ton).

Many people use these for their complete a/c system year-round, but they can be used in so many ways and are so simple to install that they’re a great short-term solution as well. The concept is simple: cold water is circulated through the copper coils of the heat exchanger and garden air is ducted over the coils and back into the garden—warm air enters and cold air exits.

They’re extremely versatile and because the air in the garden is simply recirculated over the heat exchanger and not exchanged outside the growroom, they help to maintain a sealed environment—which has significant benefits in any season.

If desired, they can be mounted to reflectors to absorb bulb heat directly, which is the way you would use them if you were not exhausting air from your reflectors outside the garden. Obviously the colder the water circulating through the heat exchangers the more cooling will be achieved, but water even a few degrees colder than the desired garden temperature will still have some effect.

Heat exchangers will require a fan to pass air across them, but the cold water can come from many sources. Most people pair an equivalent BTU water chiller with their heat exchanger, but this is usually when it’s intended as a long-term solution or for use as a complete a/c system.

Many people recirculate water from wells because this water maintains a consistent cool temperature, or even use a drain-to-waste system with city water for the hottest parts of their lights on cycle. Of course, if you choose the drain-to-waste method, you should always reuse the water for another purpose after it’s used to cool the garden.

Some gardeners have even kept their gardens cool with heat exchangers by adding a bag of ice to the cooling reservoir every day—it’s difficult to quantify exactly how much cooling you’d get in this kind of circumstance, but some folks with very small gardens have reported success with this method. No matter what you end up using for a cold water source this method of cooling can be very affordable and has the added bonus of providing extreme energy efficiency.

We promised you creativity in this article, but first there is something mundane that we’d be remiss not to mention. Boring as they might be, window-mounted a/c units can be an affordable solution for extra cooling in the garden.

They tend to be energy hogs as cooling systems go and we’d never recommend them as a permanent, complete, or long-term solution. However, if your primary concern is your budget and all you need is a short-term crutch, they might be worth looking into—just understand that the BTU specs and growroom-size ratings on most window-mounted a/c units will not apply in your garden.

Average figures for home a/c units are based on insulated homes, with typical home appliances only occasionally in use. Your garden is a much different environment, with far more heat sources than the average home—the square footage of your garden is less important to consider when it comes to cooling than the equipment it contains.

Also remember that when you use an a/c like this some air will be exchanged with the outside—and that of course you’ll have to have a window available in which to mount it.

It’s widely understood that elevated CO₂ levels in your garden will allow you to run it a few degrees warmer without adverse effects on your plants. However, a big source of CO₂ in the garden—your CO₂ generator—also creates a lot of heat in the process of creating CO₂.

When summer heat is factored in, you’ll often find that you are dealing with far more heat than can possibly be offset by the generator. One good option in the summer is to switch to bottles only for the hottest couple of months.

Using CO₂ bottles can be a pain as they have to be changed out more often than propane bottles, but for a lot of gardeners the temporary trade-off is worth it and as soon as temperatures cool off they go right back to their burners.

Other gardeners have chosen to go with a water-cooled CO₂ generator—which removes heat from the burner before it can escape into the garden by circulating water above the flame. Water-cooled generators are affordable, but remember that a source of cool water will need to be available.

Generally speaking, water in the 75 to 85° range is optimal for a water-cooled generator, as the water doesn’t need to be too cold to effectively remove excess heat. Any of the methods described above for use with a heat exchanger can be effective, but the CO₂ generator provides the added option of using a swimming pool or small pond for cooling as well, for those gardeners who have a feature like this available.

If you and your plants have been dreading the heat of summer, perhaps one of these solutions will prove to be helpful for you. Traditional cooling systems aren’t always feasible in every situation, so just remember there is a solution for every problem, big or small—and that creative thinking always yields results!