How To Heat A Greenhouse Using Compost

How to heat a greenhouse using compost

How to Heat a Greenhouse Using Compost

Most gardeners (both small or large scale) are well aware that a large heap of fresh manure, livestock beddings, or other organic farm residuals can generate substantial heat. In addition, this heat may last for several weeks or even months and that is why most farmers would opt to use it to heat their greenhouses.

You can heat a greenhouse using compost. Many studies as well as professional gardeners and “green-thumbs” have demonstrated, that decomposing organic material can generate heat and carbon dioxide that you may use to boost the health of your growing plants inside the greenhouse. 

Fortunately, new techniques have been developed and tested on how to draw heat from the compost. Unlike the traditional way of using fans to extract heat, the modern methods use water flow pipes buried underground to pass heat from the compost pile to the greenhouse. 

This article will discuss the methods of extracting heat from compost, the environmental benefits of composting, and how to heat your greenhouse with compost. 

The Basic Principles of Compost Heat Extraction and Their Benefits

Extracting heat from compost involves three integral stages

  • Heat production
  • Heat capture 
  • Heat utilization

Heat Production

During the composting process, microorganisms break down the organic matter in the compost. As the organic matter breaks down, it generates heat, water, carbon dioxide, and fertile products through microbial activity. 

Microbial activity generates lots of heat, and it can produce temperatures of up to 130° to 170° Fahrenheit, which is enough to kill weeds and harmful bacteria. In addition, this heat can be used to produce optimal temperatures inside the greenhouse during the winter and the shoulder seasons.

The oxidation process is what causes the organic material to heat up. The common assumption is this material is made up of brown and green organic material. The optimal ratio of organic material is two parts brown and one part green. This is the best ratio for generating heat without too much ammonia.

Some examples of brown materials to use are straw, yard clippings, shredded newspaper, leaves, and sawdust. Keep in mind if you’re using yard waste, remove any chemically treated items. The green materials to use are eggshells, coffee grounds, tea bags, and fruits/vegetables. This isn’t meant to be an all-inclusive list, but just some ideas.

Three Methods Of Heat Capture

Currently, there are three main methods of extracting heat from the compost. These can be through water-based or air-based heat capture or the recent condenser-type heat exchanger. 

  • Water-Based Heat Capture

Water-based, also known as the hydronic heat capture method, uses a pipe system buried under, around, or directly within an active compost pile. A water antifreeze solution is pumped through the pipes, and the solution itself will heat the water.

The heated water is then pumped to a proper heat load device (such as a flooring slab or heat exchanger) to buffer the warm temperatures and energy extracted. 

The pipe unit and heat load device connect to the expansion tank and pump in a heat exchange loop. 

  • Air-Based Heat Capture

In an air-based heat capture approach, the air is pulled down from an active compost pile through blowers. It then forces the generated compost-heated hot vapor to flow via the duct unit and over thermosiphon tubes.

A greenhouse may benefit from this method through the carbon dioxide or heat generated from the composting vapor. 

The heat from the hot vapors will rapidly be transferred by the thermosiphon within the duct unit to potable water in an insulated tank without direct energy input.   

  • Condenser-Type Heat Exchanger

A condenser-type heat exchanger isn’t really for a small home gardener (depends on how big your operation is), but will probably be used at your local greenhouse. This approach is effective but used in many commercial composting sites. 

The heat exchanger uses and pushes the heat into the compost pile upper chambers in the thermophilic stage. Once the steam condenses on the heat-exchange surface, the heat passes via the pipe through conduction to the heat transfer medium. 

Heat Utilization/Heating Your Greenhouse

Heating your greenhouse using compost heat can be relatively easy. Not everyone will have enough space to create large compost piles in their backyards but you can use compost bins to provide heat to specific greenhouse sections. 

Alternatively, you can place the plants over the top of the compost to create microclimates that will maintain the heat throughout the winter. This practice allows you to achieve various temperatures and give warmth depending on the specific plant requirements inside the greenhouse.

By leveraging sustainable ways to capture heat from compost and keep the air inside the greenhouse warm, it can allow you to plant year-round continuously, without expensive heating systems. This can be big cost savings! 

Another simple DIY concept is using two empty barrels to extract heat from the compost inside the greenhouse. This approach will provide the ideal temperatures your plants require to thrive in winter. 

  1. Place two 55-gallon barrels some feet apart inside your greenhouse. Ensure the barrels’ tops are covered, or turn the barrels over if the top is open and doesn’t have a lid. 
  2. Lay a metal wire bench top across the two barrels. Move the barrels to the sides until they support the benchtop at both ends. You will need to provide adequate space between the compost and the barrels.
  3. Place a wooden box in the space created between the two barrels and fill it with brown and green compost.
  4. Ensure the wooden box is fully loaded by refiling it with more compost. To produce heat, the compost pile has to be compacted tight. Use whatever you need to compress the pile. Too much airflow in the pile will prevent the material from breaking down and heating up.
  5. Increase the temperature a few degrees more when it reduces as the compost starts to decompose. Also, ensure you add some water to the newly created compost bin.
  6. Place the plants on the wire benchtop to receive heat as the compost slowly breaks down and releases heat. 
  7. As the material breakdown, the temperature will slowly rise. Use a thermometer with a longer stem so you can get an accurate reading. Nothing fancy is needed. 

Benefits of Composting

Using compost can heat your greenhouse, but that’s not the only benefit. Compost is great for plant health. It conserves water, which helps stave off drought. And one of its biggest benefits is it reduces waste. All the material you put into compost keeps that material out of landfills. This is a great way to reduce your carbon footprint and help prevent climate change.

Troubles Generating Compost Heat

Getting the compost mixture right and getting enough heat to be pracitcal can take a bit of science, experimentation and patience. Here’s a quick video to help you make sure you’re doing everything you can to avoid low heat.

Wrapping up Using Compost For Greenhouse Heating

Using compost for healthy soil and greenhouse heating has been a method used for centuries. It’s effective, reduces your carbon footprint, and can save you money. There are a few different ways to compost, and choosing the right one for your setup may be different than your neighbors.

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