How to heat a greenhouse using thermal mass
The main challenge with greenhouse growing is maintaining the temperature swings that we face.
The most common way people do this is by using energy via heating or cooling systems in the greenhouse.
But the better, more sustainable way of managing a stable greenhouse is to use the solar energy from the sun during the day, store it and use it at night.
You too can maintain your greenhouse temperature if you learn how to heat a greenhouse using thermal mass.
Consider heating when building
When you set out to build your brand new greenhouse – you should consider heating, cooling, and even how you will water the greenhouse.
If you plan accordingly to accommodate these things when designing and building your greenhouse – it will make your life easier!
When choosing a greenhouse design
Choose a design that will not require much in the way of heating and cooling. This means building an air-tight, well-insulated structure that is made out of the appropriate materials.
Not only are the proper building materials important – but the overall location and orientation are important as well.
Tip: For optimal natural heat and sunlight – you should build your greenhouse to face the south.
If growing in an existing greenhouse, you can insulate your greenhouse and weather-strip air leaks among other things.
This can reduce your energy requirements to a minimum and should be the first step, then implement the tips that follow.
How to heat a greenhouse without electricity
1) Store solar energy in thermal mass
The most common way to even out the temperature of your greenhouse is to use thermal mass, also called a heat sink.
Thermal mass is any material that collects and stores thermal energy. Even though a lot of different materials can be used as a heat sink there are some options that definitely stand above the rest.
Water, for instance, holds about 2 times as much heat as concrete, and about 4 times as much as soil.
Implementing thermal mass does two things. First, it absorbs excess energy during the day which creates a cooling effect in the greenhouse.
When the temperature dips down at night, it starts to release that energy, thereby heating the greenhouse. It acts like a battery-saving up energy and releasing it later.
The size of the battery (or how much energy you can store) depends on the heat capacity of the material and how much mass you have.
Below is a table with comparisons of a few different sources of thermal mass and their heat capacities.
How to heat a greenhouse using thermal mass
One of the most common ways to use thermal mass is water barrels because it has such a high heat capacity.
You can incorporate a significant amount of thermal mass by stacking several 55-gallon drums of water in your greenhouse.
Barrels should be positioned in direct sunlight, often on the North wall. The area immediately around the barrels will often be warmer so place your more tender plants there.
Growing with an aquaponics system — growing fish and plants symbiotically — has the nice benefit of the fish tanks doubling as thermal mass.
Other options include building concrete or stone into the greenhouse — such as using a concrete North wall or paver floor. Even the soil in raised beds will add thermal mass.
Heating a greenhouse with compost
Along the same lines as using raised beds in your greenhouse for greenhouse heating. You can use compost piles or bins to add supplemental heating to your greenhouse.
This is a great way to heat a greenhouse without electricity. This is one of the most common greenhouse heating systems because it is effective and affordable and it serves a double purpose both producing heat and healthy compost for your gardens.
While the easiest to install, thermal mass can be slow to react. It takes longer to release the heat throughout the greenhouse, limiting its effectiveness.
But, given the low upfront cost, adding thermal mass to a greenhouse is a great method for extending the growing season.
It may not get you year-round growth of all things, but it can certainly take your greenhouse to the next level.
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