4 season Greenhouse in Freezing Conditions: Insights and Future Enhancements

4 season Greenhouse Update during freezing winter conditions temperature log update Nov-26 to Dec-8

Our off-grid, 4-season greenhouse recently navigated a challenging period marked by heavy cloud cover, freezing nights with temperatures dipping under 16F. This period provided valuable insights into the system’s performance under extreme conditions and highlighted areas for potential enhancements.

Observations During the Cold Spell

On December 3rd, with outdoor temperatures reaching a low of 15.6°F, our indoor temperature briefly fell under freezing to 30.92°F. The thermal storage barrels, at 36.8°F, played a key role in moderating the temperature drop. The spinach tolerated these conditions with no visible affect. The willow plants exhibited some stress including loosing some leaves. This scenario illustrated the need for faster heat delivery during extreme temperature drops. It also shows the need to reduce thermal loss so the existing thermal storage can keep up. Reducing thermal losses would also have ensured the thermal storage started at a higher peak temperature which would have allowed it to deliver more BTU during the critical period.

Current State of the Greenhouse

As of December 8th, the greenhouse continues to support plant growth through freezing nights. This period has been an important test of the existing setup’s resilience and the effectiveness of implemented strategies.

Plants growing in our off grid 4 season greenhouse Dec-8 after many weeks of freezing conditions and nighttime temperature tips below 18F. See the Data logger used to gather this temperature data. It gathers 5 temperatures plus pressure data. If others are interested I can convert this to a nice looking PCB and make them available for about $150.00 each.

I love conditions that test the limits of our prior engineering so we can see what needs to be improved.

Joseph Ellsworth Dec-8-2024

Planned Improvements and Strategies

In response to these observations, several enhancements are being considered:

  • Enhanced Insulation with Additional Glazing: Initial results from installing inner glazing layers indicate a promising reduction in heat loss, potentially over 55%.
  • Light and Insulation Optimization: Combining affordable polycarbonate with insulating panes (Duck brand Window film showing over R5 and vinyl over R3.5) aims to strike a balance between insulation efficiency and light transmission.
Insulating greenhouse glazing panels. 3 Layers of plastic film forming two air gaps with a 3rd air gap formed between outer most membrane and the polycarbonate. Our existing polycarbonate has a R-Value of 1.43 less any thermal bridging in the aluminum. By measuring temperatures changes across each air gap we can determine that the new R-value is 296% of polycarbonate alone. I am still taking measurements but it looks like the R-value of with the Duck brand Window film is over R5 while vinyl version is over R3.5 I will be building a new Vinyl version using everything I learned in the first two to ensure the difference is really due to materials and not differences in construction techniques. Light transmission losses look are between 7% and 11% above the losses in the polycarbonate alone. These numbers indicate the combination of this cheap polycarbonate and the hand constructed insulating panes deliver better insulating value and better light transmission than much more expensive 25mm triple wall polycarbonate.
  • Geo-Exchange System Integration: The installation of a Geo-Exchange system is underway to supplement the thermal storage barrels, particularly beneficial during extended periods of cloud cover and freezing temperatures.
  • Automated Temperature Regulation: We are exploring the use of an automated fan system to maintain above-freezing temperatures inside the greenhouse by activating a fan whenever to blow air past the thermal barrel whenever air temperatures drop close to freezing.

Continued Learning and Adaptation

These experiences in extreme weather conditions have been instrumental in understanding the strengths and limitations of our greenhouse setup. Each observation guides us in fine-tuning our approach and informs our future decisions.

Collaborative Opportunity

We are considering making our custom-designed data logger PCBs available for others interested in detailed environmental monitoring, estimated at around $150 each.

Ways to prevent frost damage under similar conditions:

  1. Improve insulation value from the glazing to allow the heat exchange with thermal barrels to deliver heat fast enough to keep the air above freezing.
  2. Increase surface area of the thermal storage barrels to exchange more heat
  3. Increase the water temperature in the barrels so they can deliver more heat.
  4. Increase thermal exchange with the barrels using a blower when air indoor is approaching freezing so they can deliver enough heat to keep the air above freezing.

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