Using compost heat for perennial production

View the project final report

• 2013 annual report
• 2014 annual report

Commodities

• Additional Plants: ornamentals

Practices

• Energy: energy conservation/efficiency, energy use, solar energy

The expense of heating oil limits our production, thereby forcing us to lay off our two full-time, seasonal employees during the winter months. Other growers in the Northeast face the very same dilemma. Recently, we have begun growing our own perennials instead of buying in the plants wholesale. We also produce compost from plant waste and municipal yard waste from the city of Laconia. We then use the compost in our soil mix for our perennials, and are able to produce a one gallon perennial for $1.18, as opposed to $4.50 when bought through a wholesale outlet. After converting to our own production, we have established a few wholesale accounts of our own with other local growers. From these relationships, we have discovered that we have the potential to double our perennial production. However, we will have to increase our fuel consumption in heating the greenhouses during January and February. A solution to the fuel costs, as well as labor, is to use the heat that is generated from our compost pile to heat the greenhouse structure used for perennial production. For the past two years, we have been monitoring the temperatures of the compost pile during the winter months, and have found that it reaches between 140 to 155° F. Furthermore, we have discovered that to maintain these temperatures, we must maintain the mass and shape of the compost pile. Regrinding the pile provides aeration, adding oxygen, which keeps the heat building in the pile. Our idea is to remove the heat from the core of the pile to heat the perennial greenhouses to 40 to 50 F, primarily at night. We compost leaves and grass clippings, which we obtain from the city and area landscapers at no cost to us. It takes 3,000 yards of leaves and grass clippings to form the pile that we will use in this project. Landscapers must pay the town or city to take yard wastes, whereas, a grower who has a compost pile can easily use this material to build a compost pile. The turnaround of the pile is relatively quick, and we foresee a pile reaching the optimum temperatures in as little as a few months. Furthermore, we believe a compost pile will heat up faster, and requires less acreage than does the windrow method of composting. We would like to develop this project so that we can establish a heating system that will carry the heat from the compost pile to the greenhouse, while also monitoring the temperatures of the compost pile to ensure adequate temperatures to complete the composting process. By proving our theory, we can share our results and process with other growers, who can then reduce their fuel expenses and potentially increase crop production. Outreach will be via a twilight meeting, extension, and a conference.

One coil will be placed in the center of a 30 foot compost pile. A pipe will lead from the coil to a heat exchanger in the greenhouse. The heat exchanger will be controlled by a thermostat, so that when the greenhouse calls for heat, it will pump heat from the compost pile. Likewise, when the temperature of the middle of the compost pile falls below 140 F, the thermostat will call for heat to be pumped back into the compost pile. There will be insulated holding tanks in the greenhouse to capture radiant heat in the daytime to be pumped back into the compost pile when the thermostat calls for heat. The solar heat will also help reduce the demand for heat from the compost pile. This is a closed system, and will eliminate the possibility for gas vapors from the compost pile to escape into the atmosphere. Heat tubes will be placed in the greenhouse floor to keep the root zone at the optimum temperature.

We will monitor temperatures by using temperature probes that will take readings every 30 minutes throughout the day. The temperature readings will allow us to determine how much heat is generated by the compost pile and whether it is sufficient enough to maintain a temperature of 40 to 50 F for the greenhouse. We will simultaneously be measuring the temperature of the compost pile, so that we can measure the heat loss and delivery of the excess heat from the greenhouse back to the compost pile. It will also be important to observe the length of time that it takes for the compost to produce a finished product, based on the temperature readings of the pile.

To obtain temperature readings from the compost pile, we will install coil in the center of the pile. Monitors in the pile will register the temperature every 30 minutes each day of production.

• Plan of Work for Using compost heat for perennial production