Climate Battery Performance - Three Years in Review

The Beginnings of our Climate Battery Greenhouse Journey

In November of 2017, we completed work on the our first climate battery greenhouse at our home farm, Threefold Farm. It was unflatteringly and uncreatively nicknamed “The Gray House”, after the gray metal awning above its sliding doors.

At the time, we had no idea what to expect performance-wise out of the system. Most climate battery systems to that point were installed in highly insulated structures. These are often very expensive per square foot to build and are often not economical for small farms. By contrast, we installed ours underneath a relatively normal high tunnel structure, a 30x96 greenhouse with double-inflated poly cover and polycarbonate end walls, a fairly common setup on farms our size and much more economical in terms of cost per square foot.

A view of the gray house in late 2017 as the first oats cover crop is starting to germinate nicely. The row cover was an early attempt at creating an inexpensive energy curtain (it mostly failed but lessons were learned).

So how did it fare? Surprisingly Well

To be sure, the first winter with a climate battery greenhouse was rocky. It was a cold winter. We had a record stretch of days where the temperature never went above 32F. We also had a poorly-sealed structure with a lot of air leaks that we later buttoned up. We also initially over-drained our climate battery, pushing it harder than we should have due to not knowing its limits. Still, at the end of the winter we had overwintered some citrus in pots in the tunnel as well as overwintered a nice cover crop of oats and learned a lot about the limits of that particular installation.

Temperature Differential - How much warmth can the climate battery deliver into a greenhouse?

That winter we found that the climate battery could create around a 20F differential on the coldest nights, a full two climate zone difference, taking our zone 6b/7a climate to something like a zone 8b/9a. We also found that we could extend our growing season (meaning no freezes in the greenhouse) by approximately two months in the spring and another two months in the fall, with the limiting factor really being the available sun during the coldest parts of the year.

Other Benefits - Soil Pre-Warming, Cooling, Dehumidification

It should have been obvious, but a serious side benefit to the climate battery was the pre-warming of the soil in the spring. Since the climate battery uses the soil to store heat, the plant roots benefit from that rapid rise in early season soil heat, especially for heat-loving crops that we wanted to start early, like tomatoes.

Storing heat in the ground had two other side-effects: cooling of the greenhouse and dehumidification. As other growers can attest, a significant issue with greenhouses is that they get too warm, especially as you transition from winter into spring. All of that precious heat that you might wish to capture from a clear February day often needs to be vented out to avoid overheating the crops in your tunnel. The climate battery allowed us to capture most of that heat in the soil and delayed the point at which we needed to vent the heat. Because we were pumping warm, moisture-laden air underground where it hit the cool soil, condensation would form and the air returning into the greenhouse would be slightly more dry: built-in dehumidification.

Since Then - Winters of 2019 and 2020

Since that first winter, we’ve been able to refine and build on our knowledge of climate batteries: the concepts behind why they work and how they function in practice. We’ve successfully overwintered subtropical plants (figs) while giving them a jump on the growing season, all for very low operating costs. There’s certainly more I want to discuss here but that will have to wait for another blog post.

Figs at sunset inside the gray house, August 2020

Ideas for the Future - How can climate battery greenhouses be better?

That first (mostly) successful winter with our first climate battery greenhouse got me to thinking: could these be even better?

Less expensive and painful to install?

Even less expensive to run?

Store and retrieve heat even more efficiently?

As a result, later that next year we started our partnership with Penn State University engineering students to begin studying climate battery greenhouses in earnest to understand the fundamentals of how and why they worked.

As we continue to learn more, we build those findings and own growing knowledge base into each of our designs and use it to inform the advice we give to growers wanting to implement a climate battery of their own. That’s why we started Atmos: to serve the grower and provide a viable alternative to traditional greenhouse heating.