User:Mike Stiles

I am an energy engineer and researcher with a Ph.D. in Biophysics from Syracuse (USA) University. I develop energy audits, feasibility studies for combined heat and power and electrification projects, building energy models, and other activities in the commercial, industrial, and agricultural sectors.  I have 30 years’ experience in energy analysis and technology and hold three US patents in solar energy.

This page results from my ongoing interest in the potential of greenhouses for growing winter crops locally with a minimal energy footprint.  I'm based in Upstate New York, which will be the point of departure for sundry topics.

I would like to use Appropedia as a forum for exchanging both technical developments and practical wisdom. In the course of this exchange I will share recent publications and open a discussion on the energy analysis of Frostbelt winter greenhouses. I will also link articles and publications of the near future to this page, using it as a touchstone for interested parties.

Thanks for visiting, and I look forward to your insights and what you've been up to!

General note to visitors: To access the documents ("Contributions") that I've posted, click on the Tools arrow in the upper right corner and select "User contributions." It will take you to the page where I uploaded documents (usually PDFs). You can download a copy from there.

7/8/25 First upload under Contributions: "An ASHRAE Level 2 Model for Transparent Greenhouse"

7/11/25 First upload of a greenhouse image (this wiki is really easy to use!)

Working draft of discussion topics forthcoming:

• Shell retrofits and energy usage
• Potential retrofit techniques, issues, and layout suggestions
• Notes on operator requirements

7/15/25  First look at insulating an 8’ by 16’ polycarbonate greenhouse to reduce winter heating usage

User Contributions file:

07 15 25  Heating Energy Study of an 8 by 16 Polycarb Greenhouse (Albany NY USA)

This analysis is based on the methodology of the ASHRAE Level 2 paper posted on 7/8/25.

The purpose of the analysis was to get a rough idea of how well commercially available insulation (1” R5 styro board) reduces the winter heating requirements at greenhouse temperature setpoints suitable for tomatoes (daytime setpoint temperature 70F, nighttime 64F).  There was the simplistic assumption that the insulation for the roof and the south-facing greenhouse side wall is removed during daylight hours and put back into place for the nighttime.

The analysis does not account for any other important factors like humidity control, lighting requirements, the costs for the plants and their upkeep, how the insulation is moved between day and night, and so forth.  These will be topics for consideration in future posts.

These preliminary calculations suggest that retrofitting the styro board insulation decreases the winter heating requirement from 227 therms to 177 therms, a 52% reduction.

Simple payback is calculated by dividing the the cost of the retrofit by the annual cost savings due to the retrofit.  Assuming only the cost for the styro board without installation labor costs, the simple payback from this arrangement is under a year for both propane and electric heating units in this greenhouse.

So the initial results are encouraging for a deeper dive for Frostbelt regions in North America using Albany NY (latitude 43^o N) as an example. As other factors are added into the analysis, the goal is to estimate the energy cost per pound of tomato that can likely be grown under the conditions outlined above.

8/4/25  First round of email responses from friends and colleagues has come in (they’re not quite up to the Contact service up top yet I suppose).

A clarification is in order from those exchanges:  This project is directed primarily towards small-scale operations.  What I have in mind is a small neighborhood co-op style arrangement that can provide fresh food for a small number of families throughout the winter.

In terms of absolute energy and water savings, it will be catch-as-catch can using household resources to get the job done.  There may be economies of scale for slightly larger versions of what I’m proposing if it’s done on a working farm.

I’ll develop this topic as I go along.  The main energy benefit I can see is avoided diesel usage for transporting the tomatoes from hundreds or thousands of miles away.

10/21/25 I've tried posting short articles that link to this page. A common feature seems to be limitations in formatting. So here's the blurb FYI:

The Winter Tomato Challenge was motivated by two major factors.  The first is that nearly all the advanced Controlled Environment Agriculture (CEA) I’ve encountered is optimized for the larger commercial operations.  This project is directed primarily towards small-scale operations.  What I have in mind is a small neighborhood co-op style arrangement that can provide fresh food for a small number of families throughout the winter.

The second motivation is that much of the developmental engineering these days for CEA is via computer simulations (I’m guilty of it myself!).  I decided to explore a project with readily available materials and build it up rather than simulate it down.  I’ll return to engineering analysis once I have some designs by people who have done them before or have enough practical experience to suggest how to go about it.

In terms of energy and water savings, it will be catch-as-catch can using household resources to get the job done at the scale I’m talking about.  A set of best practices might even emerge over time.  There may be economies of scale for slightly larger versions of what I’m proposing if it’s done on a working farm.

Experience advises me to target the project to about the 40^th to 55^th latitude north.  The sun stays reasonably high above the horizon at these latitudes for at least a part of the winter.

Getting into specifics, I’ve been looking at greenhouse kits like the one on the left in the picture below. This one is 8’ x 16’ and made of polycarbonate panels.  A Google search will give you plenty of examples that can be bought at stores near you.

The sketch on the right is an inclined trellis that maximizes light onto the plants from the south wall and roof.  One of the first things I considered was insulation.  My elementary starting example was for 1” thick (R-5) styro boards mounted securely on the east and west end walls (including the door) and the north wall and roof.

I assumed moveable insulation for the south-facing roof and wall (put up at night and taken down during the day).  At the latitude where I live (Albany NY, USA 43^o N) I found that this arrangement can reduce winter heating requirements by about 52% in a year of typical weather.

I’d apply highly reflective paint on the inner sides of the insulating panels that are fixed in place. This will diffuse and re-direct the sunlight to partially compensate for the fact that those walls are opaque.

There are practical matters of how to mount both the fixed styro boards and the moveable ones.  What bracketing would be best?  Will there be issues with condensation build-up between the styro and the greenhouse walls?  How might this promote problems with fungus and mold on the plants?  Can any portion of the interior condensate be reclaimed?

This is but a first step. There are considerations for materials, equipment, and methods of deployment for temperature and humidity regulation, ventilation, and lighting.  All these factors will interact with each other.

I want to talk to as many people as I can about these considerations before trying to simulate their energy performance.  And ideally, if a real-life project emerges from this discussion, I’ll have data to compare with my calculations and for a cost/benefit analysis.

My mission is to combine my energy engineering expertise in building science with greenhouses at a neighborhood scale.

There are links to selected publications at the home page as well (Tools > User Contributions). Anyone interested in the energy calculations I use for greenhouses can find them at:

https://www.appropedia.org/File:An_ASHRAE_Level_2_Model_of_Transparent_Greenhouses_IJEM.pdf

Please initiate outreach through the Contact link at the top of the Appropedia home page.  Thanks for reading this, and I look forward to hearing from you!

11/4/25

I’m getting a few hits at other sites, this one includes an actual response:

https://www.reddit.com/r/verticalfarming/comments/1o30jh8/comment/nlvhhd4/?%24deep_link=true&context=1&correlation_id=d16e24f6-cb4f-5361-8ec8-d766a301f448&ref=email_comment_reply&ref_campaign=email_comment_reply&ref_source=email&%243p=e_as&_branch_match_id=1512852037507268019&utm_medium=Email+Amazon+SES&_branch_referrer=H4sIAAAAAAAAA31Qy07EMAz8mu6t7bbJhgqpQgjEb0Rp4rZZ8pKTbuHCt%2BPCckVypMl47Bl5LSXlx7ZFMMaWRqXUOBveW5aeqp6zNIJU%2BUQwol1sUE5u6Mb1mKrYc9W%2FUe373tzndfREIL0bYLFauVmht2EhhnoeQskEu8jO13UglL1yLpMOZLEpyzmiVHIC8gpw7Anutq6GH06MzC49NwBJHiEr9lpwg6oXOoYCH4WI7ueHCE4VG4O0hkjTCej5LGo98bm%2BMNHVA%2BihNg9CKHbuZs4pi0CYSQxeWSfvYSVCcp%2B%2FPamVT8ou4V9Rjhtq%2BJOcvogDRLqAnDDuGXB8WTF6%2BAaM6StzeQEAAA%3D%3D

Reddit is the most promising Greenhouse group I’ve come across to date. I’m still searching and networking and will post as things turn up.

But back to Things that Work, my next project is to combine the following technical analysis of Chinese greenhouses with similar analysis I’ve done over the last 20 years:

https://www.fao.org/4/t4470e/t4470e0c.htm

The results will probably be the basis of my next publication.  Happy winter here in the north hemisphere and happy summer down under!

Update:  I just found a very informative example of a geodesic dome (shell appears to be at least one layer of bubble wrap) at

https://brenhaas.com/turning-on-the-dome-heater/

Location is Ohio (USA).  A propane heater with a 45F setpoint is shown in the YouTube video at the link.  User reports spending about $200 over the winter in propane.  Time to do a bit of modeling…thanks Bren Haas!

1/9/26 Permaculture site with plenty of “hands on” suggestions

https://permies.com/

Today’s Example

Mike Haasl: “My mission is to create a greenhouse that allows people in a cloudy and frigid environment to grow food year round.”

https://permies.com/t/76165/Mike-passive-solar-greenhouse-design

Summary of Mike’s design:

-20' by 40' by 16' high structure on a frost protected cement footing at grade.

               Comment:  More elaborate than a polybcarb unit; good point about frost protection at ground level, especially where the walls meet grade

-Cement block pony wall 32" high on the footing to allow for snow shedding and elevation variation across the site; fill all the voids in all the block with mortar/cement.

               Comment: It’s important to fill the voids to prevent cold air looping inside the blocks

-Curved web trusses made on a jig

-Heavily insulated North, East and West walls

               Comment: He suggests styro board but does not consider the issue of moisture developing between insulation and shell

-The walls won't form a gothic arch.  The South wall will overshoot the North one to increase glazing and get sunlight farther into the back of the greenhouse in the summer.

               Comment:  This is based on Chinese designs; for the Frostbelt the problem isn't summer sun but low angle winter sun

-Vents low on the South wall and at the peak for summertime ventilation

               Comment: Could be a problem sealing them in the winter

Here are Mike’s thoughts on shell insulation:  “Glazing is 85% of the heat loss.  My plan is to attach 1x4 boards to the bottom of the South wall trusses to act as small ledges.  Then a 4' wide roll of Reflectix (or equivalent) insulation will be attached up at the peak of the roof.  It will roll down on the ledges until it ends up at the bottom of the wall. Effectively sealing off each truss bay. If the Reflectix wants to sag due to the 4' span I can simply run 50 lb fishing line E/W across the bottoms of the trusses before I attach the ledges.  The insulation rolls will act like the sort of window blinds in the attached picture.  They'll raise and lower via strings that attach to a pipe at the peak.  Rotating the shaft will raise and lower the rolls. Initially I'll control them by a bike chain and crank on the wall.  Once I get the kinks out of the system I'll hook up a motor to it.  I believe the Reflectix will add R3 to the glazing which will be huge.”

Mr. Haasl also provides a sketch of his design that is worth checking out --

1/12/26

A few exercises using the calculations posted here at Tools > User Contributions > 07 15 25  Heating Energy Study of an 8 by 16 Polycarb Greenhouse (Albany NY USA)…for the 8’ x 16’ polycarbonate greenhouse shown at the top of the page

First, I wanted to roughly compare the energy usage reported in the 11/4/25 entry above by Bren Haas of Ohio with my model for the polycarb unit. According to her blog, her 20’ geo dome covered with bubble wrap needs about $200 in propane to maintain a 45F setpoint.

Bren’s geo dome is roughly comparable in size to the 8’ x’ 16’ unit. Both have a shell insulating value in the R-1 to R-3 range, and Ohio isn’t that geographically distant from New York.

A quick Google search suggested a ballpark price of propane in Ohio around $2.50/gallon.  That gives about 80 gallons, which at 0.91 therms/gallon for propane gives about 72 therms for Bren’s annual heating usage (one therm is equal to 100,000 Btu).

I used a 45F setpoint for my model of the 8’ x 16’ polycarb unit.  The heating requirement came in not at 1 therm or 1000 therms, but at 100 therms.  (That’s 80 therms needed to keep the thermostat at 45F divided by a typical propane heater efficiency of 80%).  These calculations took a lot of liberties, but the results are in the ballpark – the two estimates are within about +/- 30% of each other.

Today’s second item concerns a common question on forums like Reddit: “How much shell insulation is needed to cut heat fuel usage in half?”  So, I added shell insulation to the basic 8’ x 16’ polycarb unit in the model and re-calculated annual heating requirement.

I put the setpoints at temperatures suitable for growing tomatoes (70F during the day and 64F at night).  The results (assuming a propane heater) are plotted in the graph at the right.

The shell of the polycarb unit has an R-values of about R-1.6.  The R-value of the insulation added to the unit’s shell is plotted on the horizontal axis.  For example, adding R-1 to the basic greenhouse would result in a net value of R-2.6.

The blue line in the graph is the annual heating requirement to keep the greenhouse at the setpoint temperatures (in Albany, NY).  With no added insulation, the propane requirement is estimated at about 283 therms.  Adding R-1 of insulation drops the requirement to about 210 therms, and so on.

The orange line is the energy savings due to the added insulation.  The graph shows that cutting heating usage in half would require about R-3.5 of added insulation (for a total shell value of R-5.1).

The trends shown in this example graph are typical: There are diminishing returns on energy savings as you add more insulation (the effect is tempered by ground-coupling).  These types of calculations are the basis for deciding how much insulation is cost-effective given your goals of greenhouse temperature settings, crop selection, and desired crop yield.

1/16/26

Summary outline to date for the Winter Tomato Challenge using a small greenhouse

The various systems have options for automation, which increases cost and complexity.  Manual operation would probably require the operator to be in close proximity to the greenhouse at all times (especially if using moveable insulation).

The skills required to operate a Winter Tomato Challenge greenhouse include knowledge of basic HVAC (heating, ventilation, air conditioning), electronics, construction, and horticulture.  These skills could be acquired from BOCES-level training.

The best website I’ve found to date for practical considerations of what works and what doesn’t:

Buildings:   https://permies.com/c/6

Energy:  https://permies.com/c/7

2/13/26

Links to some advanced winter greenhouse projects

High Efficiency Year-Round Tropical Greenhouse

https://projects.sare.org/project-reports/fnc19-1185/

Deep Winter Producers Association

https://www.facebook.com/groups/845092875544652/