Climate Battery Design Comparison - Why Design Matters
A question we receive: “Why shouldn’t I use a free design off the internet?”
It’s a valid question. Climate batteries have been around long enough that there are some plans and plenty of images of installations floating around on the internet (including some of our own climate battery greenhouses at Threefold Farm, the Gray House and the Blue House).
So why spend money for Atmos’ designs when other plans are free? That’s what we’ll break down in this article.
Design determines performance… for life
A climate battery installation is a long-term investment. It will likely outlive even your metal greenhouse frame, and it’s very nearly impossible to make modifications once it’s in the ground. Therefore, it’s important to get the design right from the get-go.
Why? Because the piping layout forever determines the maximum performance you can expect out of the system. This, in turn, drives your operating costs and your expected return on investment (ROI).
But don’t most designs work well?
At Threefold Farm, we’ve been pleased with the performance of our climate batteries. They perform well for our farm in our context and are inexpensive to operate.
That said, the existing designs have significant flaws. Our studies with students at PSU and Sawyer (our 3D modeler here at Atmos) have identified two big problems in the the tubing setup. First, the airflow isn’t balanced. Some tubes get a much larger share of the airflow from the fans while some tubes are starved for air. Second, the tubing layout creates unnecessary back pressure through multiple hard bends in the piping. This, in turn, reduces overall airflow, leading to lower performance of the system. Why are these two factors so important?
The Importance of Balancing Airflow - An HVAC Example
Think of the HVAC ducting within a home. If a home’s HVAC ducting is poorly designed or installed, one room might be freezing cold while another is toasty warm. At one time or another, we’ve all been in a house or room like this. This occurs because of imbalanced ducting. Too much of the heat or too much of the chilled air is going to one room or a set of rooms.
The same sort of problem can happen in your climate battery: if airflow is not relatively even across the pipe array, the system won’t be able to cool and heat as effectively as it would with a more even air distribution. As a result, there will also be portions of the soil that will be significantly warmer and cooler than others. The system on which you worked so diligently won’t be as effective as it could be.
The Importance of Reducing Back Pressure (Static Pressure)
Think of watering with your typical garden hose. The longer the hose is, the more obstructions, the more twists and turns and partial kinks or restrictions, the less the resulting flow of water that comes out of it. Air, like water, is a fluid, and follows much the same principles for flow, thus the example holds for designing a climate battery.
In a climate battery, we not only want to balance airflow, but also to ensure that we’re not creating any unnecessary restrictions to that airflow due to our piping layouts. Restrictions will reduce overall airflow, thereby reducing performance. Obviously some restrictions such as bends and turns are necessary to distribute air where it needs to go, and our goal in design is minimize them, thereby reducing back pressure.
The rainbow of colors here may be quite pretty, but it points to the fact that airflow is very much unbalanced across the tubing setup, leading to significantly reduced performance.
Once again, as in the above video, the range of colors means uneven airflow. The blue pipes are starved for air while the red pipes receive the bulk of it.
The Beauty and Value of a Good Design
Let’s dig in further and compare and contrast a poor design and a good design.
Poor Design
Poor Design → Wasted piping → Higher running costs & Missed season extension opportunities → Longer Payback Period
Poor designs lead to inefficient air distribution. Inefficient air distribution leads to inefficient heat transfer and wasted piping. Inefficient heat transfer leads to spending more time running your fans. Spending more time running your fans means you’ll spend more money in energy costs and also need to either vent excess heat earlier. Spending more money on energy costs and the need to vent heat (rather than store it, especially at key times of the year) leads to a reduced opportunity to further extend the growing season. These factors combined lead to a longer payback period.
Our Gray House, an early design, has a flow rate of ~2,050 CFM with a 0.57” static pressure. Hard angles in this fairly standard climate battery tubing layout mean that airflow is heavily unbalanced. This system still performs, but a majority of the tubing is doing very little work. Imagine how a well-designed tubing layout would function!
Good Design
Good Design → Effective Tubing Use → Lower Running Costs & Increased Season Extension → Shorter Payback Period
Good designs are quite different. Good designs more efficiently distribute air through the climate battery tubing and utilize fans performance-matched to the design. This, in turn, means less time running the fans because all of your piping is doing a greater share of the work. This in turn leads to lower operating costs, an ability to store heat (rather than vent it) later into the season, leading to increased opportunities to further extend the growing season. These combined factors lead to an accelerated payback period.
The Atmos Version 1.2 design reveals a more balanced airflow distribution with a flow rate of 3,500 CFM at 0.33” static pressure with our specified fans. The increased airflow and relatively equal distribution of air means the system should perform well for life.