Why Design Matters

Does the design of a climate battery, its tubing layout and fan selection, really matter all that much?

Would it be better to save money and just go with a design I found on the internet?

Don’t most designs work pretty well anyway?

Let’s explore…

What Guides our Designs at Atmos?

  • Air by Alvida Biersack from the Noun Project

    Increase Airspeed

    Selection of a climate battery design, the tubing layout along with the properly sized fan, determines how quickly air will move through the piping. This speed is directly affects the rate of heat transfer.

    The goal - Aim for a velocity of at least 4 m/s across all heat transfer tubing

  • balance by zakiaalfitry from the Noun Project

    Balance Air Distribution

    The layout of a climate battery tubing determines the path air will prefer to take when passing through the piping layout.

    The goal - Distribute air as evenly as possible throughout the entire tubing layout

  • pressure by Smalllike from the Noun Project

    Lower Back Pressure

    Unnecessary bends and restrictions create back pressure, making climate battery fans work harder than they need to and leading to reduced overall flow rates.

    The goal - Distribute air as evenly and efficiently as possible while minimizing static pressure, leading to increased flow rates.

Learn More in our Blog on Design

What Are The Benefits Of Good Design?

  • Lower Operating Costs

    Since more effective tubing layouts and proper fan selection lead to more effective heat transfer, this means heat is extracted more efficiently. This, in turn, means that fans cycle on and off less frequently.

    The end result, lower operating costs for the life of your greenhouse.

  • season by Wichai Wi from the Noun Project

    Season Extension

    Since heat is more efficiently stored in a good design, there is a greater opportunity to capture heat rather than vent it outside the greenhouse. This is especially important in the critical shoulder seasons of spring and fall where days are sunny but the nights can be cold. Heat that would otherwise need to be vented to avoid overheating the greenhouse can now be stored underground.

    The end result, a greater opportunity to further extend the growing season.

  • payback by Icons Producer from the Noun Project

    Shorter Payback Period

    Climate batteries are expensive to install, so it’s critical that the install pays for itself in the shortest timeframe possible. The lower operating costs, more effective tubing usage, and increased ability to extend the growing season work together to the benefit of the grower.

    The end result, a shortened payback period versus less optimized designs.

 Comparing Two Designs

At Atmos, we don’t guess as to how well our climate battery designs will perform. We evaluate our designs using CFD, computational fluid dynamics, a way to simulate air movement in the system using 3d models and physics simulations.

Sound fancy? It is. Sound confusing? It can be. Overkill? We don’t think so.

This technology allows us to simulate how piping layouts with our selected fans will behave before a single pipe is placed in the ground. As a result, this allows us to tune designs to achieve the best possible performance at the lowest possible cost for our customers.

CFD allows us to visualize air distribution, view air speed in the piping, as well as see constrictions that may be reducing performance. Let’s take a look at two different designs…

Atmos Version 1.2

Visual CFD analysis of the Atmos Design Version 1.2 shows relatively equal air distribution and air velocities exceeding our ideal minimum*

CFD Analysis

Air Distribution (Equal Distribution is best)

Air is distributed relatively evenly across all lengths and layers of piping. The coloring of the piping would indicate that most of the air velocities are in the 4.5-9 m/s range, meaning there is some difference but it’s not drastic.

Air Speed (Higher is better, to a point)

We aim for an air velocity of at least 4 m/s across our tubing to maximize heat transfer while minimizing fan electric usage*.

This design has most velocities in the 4.5 - 9 m/s range.

Flow Rate
(Higher, meaning less restrictive, is better, to a point)

The flow rate of this design with our specified fans is ~3,500 CFM at 0.33” static pressure. Flow rates in real world may drop due to corrugations in the piping and additional bends and other restrictions in the piping layout.

 

Gray House (Threefold Farm)

Visual CFD analysis of this conventional design shows its flaws: hard bends and a poor tubing layout lead to unbalanced airflow and a small minority of the tubing doing a majority of the work.

Visual CFD analysis of this conventional design shows its flaws: hard bends and a poor tubing layout lead to unbalanced airflow and a small minority of the tubing doing a majority of the work.

CFD Analysis

Air Distribution (Equal Distribution is best)

While the rainbow effect is attractive, it points to the fact that there is a very large difference in airflow across the piping, meaning that a good portion of the piping is doing little to no work while a smaller percentage of the piping is doing the large share of the work. There is likely a tenfold difference between air velocities in the slowest tubes (in blue) and the fastest tubes (in red).

Air Speed (Higher is better, to a point)

We aim for an air velocity of at least 4 m/s across our tubing to maximize heat transfer while minimizing fan electric usage*.

This design has most velocities in the 0.5 - 6 m/s range.

Flow Rate
(Higher, meaning less restrictive, is better, to a point)

The flow rate of this design with installed fans is ~2,050 CFM at 0.57” static pressure. Hard bends and a design that lends itself to unequal air distribution leads to a poor flow rate. Flow rates in real world may drop due to corrugations in the piping and additional bends and other restrictions in the piping layout.

* Numerical simulation of soil heat exchanger-storage systems for greenhouses, Gauthier, 1997 https://www.sciencedirect.com/science/article/abs/pii/S0038092X97000224