An Energy Efficient Season-Extension Bunker

A n I n s t r u c t i o n M a n u a l

Prepared for: Farm Energy Working Group Prepared by: Jason Gomes, Rainbow Ridge Farm Date: January 2011

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Table of Contents

INTRODUCTION 3

PROJECT NEED 3 PROJECT CONCEPT 4 DEMOLITION 5

WALK-IN COLD STORAGE 6

MATERIALS SELECTION 6 CONSTRUCTION 6

DRYING/CURING CHAMBER 12

CONSTRUCTION 12

GREENHOUSE RECONSTRUCTION 13

MATERIALS SELECTION 13 CONSTRUCTION 14

RESOURCES 17

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INTRODUCTION The purpose of this project was to remodel/retrofit two existing on-farm bunkers to serve as an underground cold storage chamber for produce on one side, and a curing/drying chamber for produce on the other side. The remodeling project was be designed around the following principles:

A greater reliance on on-farm energy resources Energy efficiency and conservation Renewable energy usage (solar) Re-purposing of existing farm materials Passive Solar Design (operable windows and vents, South-facing

structure, critical eye toward material selection: concrete/foam mix for walls)

The project was designed to more efficiently utilize two existing underground bunkers on the farm. These framed in storage units are located under the coordinator’s garage – with one side formerly used as a woodshed and the other side with a degraded greenhouse-type structure attached to the south. Because of their positioning – underground, facing south, and with only one exposed side, they were excellent candidates for a repurposing/remodeling project with a mind toward increasing energy efficiency. Using minimal resources, some skilled labor, and the right building materials, this makes an excellent demonstration project for many farmers with under-utilized outbuildings or even walkout basements. The remodeling project resulted in an energy efficient cold-storage chamber and a solar-powered curing/drying chamber for season extension of sustainably produced food.

PROJECT NEED Curing/Drying Chamber Primary Needs: Curing Potatoes Curing potatoes requires warm, humid temperatures – preferably in the 75 to 85 degree range. Potatoes must be protected from sources of direct or indirect sunlight to prevent them from turning green. Curing Sweet Potatoes For curing sweet potatoes, late fall sun is usually sufficient to partially cure skins, but the outcome is highly dependent on favorable weather (sunlight and warm temps). The tubers tend to cure either more slowly (at best) – or only partially (at worst) when the drop in nighttime temperatures can be significant, or when daytime highs are in the mid 70s or below. A goal of the proposed curing system was to capture solar heat during the day and maintain a sufficient curing

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temperature during the night (roughly 75 to 80 F) either through use of supplemental heat or through conservation of daytime solar heat. Drying Onions/Garlic Onions and garlic require a warm, dry environment with good air circulation to cure for storage. Both crops are harvested at least 3 to 4 weeks prior to potato/sweet potato, so use of the chamber for drying bulbs will not interfere with its’ use as a curing chamber for tubers. Fans will be used as needed to maintain airflow and reduce humidity. Curing/Drying Chamber Secondary Needs: Starting Curcubit Seeds The passive solar unit will also serve as a small greenhouse for starting plants. Melons and Squash are transplanted around the 3rd or 4th week of May, so seeds will be started around mid-April. The greenhouse will have the capacity for 2 to 3,000 plants started in 72-cell trays. Use of the unit to start plants will not interfere with its’ primary purpose as a curing/drying chamber. Cold Storage Bunker/Walk-in Refrigerator Primary Needs: Root Vegetable Storage The basic need served by the cold storage bunker is the storage of root vegetables to extend the marketing season of the farm. The walk-in refrigerator in this bunker will cool efficiently and allow for durable storage of potatoes and sweet potatoes through the months of August/September/October using a refrigeration unit. Potatoes/Sweet Potatoes will be stored at high humidity at approximately 40 degrees. Use of the refrigeration unit is not anticipated for the late October through the winter months. Insulation and use of heat from the curing/drying chamber is expected to produce in the walk-in from freezing over the winter months.

PROJECT CONCEPT The walk-in was designed for late-summer, early fall use at moderately cool temperatures (low to mid 40s). These temperatures extend the marketable life of potatoes by 4 to 6 weeks. During the late fall and winter months, the walk-in is intended to function more like a root cellar. It’s design is to provide sufficient insulation from the outside to maintain storage temperatures in the mid-30s. The original concept for the project involved the use of concrete infused foam for the walk-in refrigerator walls. Use of concrete for the walls was determined to be too cost prohibitive as it would have resulted in the project going considerably over-

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budget. In addition, the concrete infused foam – though possessing excellent insulation properties – was determined to be excessive for the rather basic project need of short-term storage for root vegetables.

DEMOLITION The east bunker was originally purposed as an over-wintering room for outdoor plants. Its’ concrete walls were lined with glued-on white Styrofoam and secondary heat was provided by a black Coleman outdoor grill connected to the homes LP supply line via a steel lined hose. A greenhouse attached to the south side of the east bunker had a partial concrete base and was framed with storm-windows attached to 2x4s with 2x6 base and corners. The roof was a lean-to covered with clear fiberglass roofing and lined with a layer of clear plastic on the inside. The west bunker was used as a wood shed and for miscellaneous storage. One wall was partially lined with rusted, steel shelving. The east bunker was lined with coarse, 1” gravel flooring; the west bunker floor was a mixture of coarse gravel and sand. Demolition required two full dumpster containers for the foam, wood, windows, shelving and miscellaneous junk. Two woodchucks and numerous bats were evicted in the process.

Figure 1: Greenhouse site after initial concrete work, prior to construction.

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WALK-IN COLD STORAGE MATERIALS SELECTION Scaffolding (to hang refrigerator): 4x4 posts 2x6 cross supports Deck screws Wall: 2x6 (base) 2x4 (wall) 1 ½” Rigid Foam Insulation (R-Value 7.5) 2” Rigid Foam Insulation (R-Value 10) 4 mil plastic moisture barrier Mold resistant sheet rock (interior) Vinyl siding (exterior) Insulated Steel door A refrigeration unit from was selected that was sufficient to cool a 12x9 foot room. The unit & compressor were purchased and installed using a local commercial refrigeration company. CONSTRUCTION A simple scaffolding was constructed to hang the refrigeration unit from the center of the walk-in. The unit was installed using an accordion lift from a local rental company. The wall on the south side was a basic 2x4 construction. Studs were placed approximately 2 feet apart and the interior was insulated with stacked rigid foam – one sheet of 1 ½” and one sheet of 2”. A plastic moisture barrier was tacked to the interior and exterior of the wall. The interior siding used was mold-resistant sheet rock, with vinyl exterior siding used on the outside wall. The door to the walk-in is a standard, steel exterior door with insulated core.

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Figure 2: Scaffolding to hold refrigeration unit, 4x4 & 2x6 frame.

Figure 3: Wall base of 2x6, buried in gravel filled trench.

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Figure 4: 2x4 wall frame.

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Figure 5: Interior wall lined with 4 mil moisture barrier and mold resistant sheet rock.

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Figure 6: Walls are filled with rigid foam insulation; 2 inch R-10 and 1 ½ inch R-7.5.

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Figure 7: Completed walk-in with exterior moisture barrier. Outside will be finished with vinyl exterior

siding.

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DRYING/CURING CHAMBER

Figure 8: Photo facing towards back of east bunker. Styrofoam siding was removed during demolition phase. The small outboard motor at the lower left of the photo is a Johnson, circa 1960s.

MATERIALS SELECTION & CONSTRUCTION The Curing/Drying chamber required a lot of clearing out, but nothing in the way of additional materials. A small electric shop heater was purchased to provide a secondary heat source to allow for curing during cool fall weather and to maintain heat during night time. The original Styrofoam siding was removed to allow for power-washing of the bunker walls. The importance of cleaning the structure to prevent mildew or fungal disease was deemed a higher priority than preserving the minimal insulation value offered by the siding.

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Figure 9: Photo of drying/curing chamber from the rear facing south. Pipe sticking up from floor is drainage tile.

GREENHOUSE RECONSTRUCTION

MATERIALS SELECTION Cement blocks and mortar 2 “ steel arches 2” steel poles with mounting feet 1” steel cross supports 2x6 Trex composite decking material for base Twin-wall polycarbonate sheeting Teks screws/neoprene washers Aluminum Tape Aluminum flashing

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CONSTRUCTION An existing cement block base was extended on the south and west sides of the greenhouse. The composite-decking base was mounted to the base using anchor bolts set in concrete. Composite-decking was also mounted to the garage with an 8” strip of aluminum flashing to extend over the greenhouse roof.

Figure 10: Greenhouse framing. Cement walls were repaired/extended on south and west sides. Base of

greenhouse was constructed of 2x6 composite decking material.

Steel arches and poles were mounted to the composite decking with mounting feet. The arches were modified from a pre-fab set purchased at Nolt’s Midwest Produce Supply. Cross supports were installed at approximately 4 foot intervals, and the polycarb sheeting was attached to the cross supports using self-drilling screws.

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Figure 11: Finished greenhouse exterior.

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Figure 12: Finished greenhouse interior.

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RESOURCES Canada Plan Service, 6000 Series. (http://www.cps.gov.on.ca/english/fv6000/fv6319.htm) provides some basic principles for walk-in cooler design, along with some other plans for vegetable storage structures (http://www.cps.gov.on.ca/english/fv6000/fv6000.htm). http://web1.msue.msu.edu/imp/modp1/morefile/E0104.pdf Numerous states extension services provide root cellar or cold storage design. This plan from Michigan (Extension Bulletin No. 104) is from the 1930s, and still relevant for DIY storage. http://www.storeitcold.com/ CoolBot has some technology that can use a simple window AC for walk-in refrigeration. I’m not sure how – or whether – it works, but they do also have some good DIY notes for cooler design available on their website. Root Cellaring, Mike & Nancy Bubel. Available through Fedco Seeds (fedcoseeds.com)