14 Strategies to Keep Your Fruiting Chamber Cool in Hot Climates

Mushrooms are growing almost everywhere. They are tasteful. They are healthy[1].

It is, therefore, no wonder that people start to cultivate them around the world. But growing them in an artificial environment is a challenge of its own.

There are many things like sterilization or the growing conditions which can go wrong. I wrote about both topics in the following articles.

The last reason the growing conditions is something many not only beginners struggle. This is especially true if you are living in a warm or hot dry climate and, even worse, a warm, humid, or hot, humid climate.

But it can be done. How it can be done is part of this article. In it, I will give you first a general overview of the challenge and then present you with 14 strategies to reduce the struggle and make your life easier.

You can choose which one do you want to apply to your fruiting chamber. But keep in mind the more ways/strategies you use, the easier it is to maintain the conditions.

Definition of the outside conditions

To define the external conditions, we take a look at two climate zone maps. The first figure (1) shows the climate zone map of Australia and the second as well as the third one, the climate zone map of the USA (Fig. 2 and Fig. 3).

climate zone map Australia

Figure 1: Australia climate zone map[2]

climate zone map USA

Figure 2: USA climate zone map[3]

Climate zone definition USA

Figure 3: Definition of climate zones in the USA[4]

Definition Australia USA
Zone 1 High Humid Summer, Warm Winter Hot and Humid
Zone 2 Warm Humid Summer, Mild Winter Hot and Humid
Zone 3 Hot Dry Summer, Warm Winter Hot and Dry or Hot and Humid, if below the white line (Fig. 3)
Zone 4 Hot Dry Summer, Cold Winter Mixed Humid

Table 1: Definition of climate zones for Australia and the USA[5].

There are other climate zones, but for this article, I will only focus on these four categories. If you live there, you can still take advantage of the information in this article and improve the climate within your fruiting chamber.

But what does warm and hot or dry and humid mean?

Let’s start with dry and humid. Dry is defined by less than 500 mm per precipitation year with month having less than 60 mm precipitation. Likewise, humid is defined if the precipitation is higher than 500 mm per year.

If we look at the next chart (Fig. 4), which describes the monthly rainfall for Darwin, Australia (climate zone 1). We see months with very high rain and months with almost nothing.

While the blue line indicates that Darwin could fall in the definition of a humid region (at least in some month), the orange line (average) and especially the yellow line (median) are telling us something different.

According to these two lines, Darwin falls in the category dry and, therefore, as we already know in the climate zone 1.

Monthly rainfall in Darwin, Australia, climate zone 1

Figure 4: Monthly rainfall in Darwin, Australia, climate zone 1[6]

Figure 5 illustrates to get a better understanding of the situation, the frequency of rainfall for Darwin. The majority (80 %) is below 300 mm.

Precipitation per year for Darwin, Australia (climate zone 1)

Figure 5: Precipitation per year[7]

What about the temperature? The tropical climate is defined as an average temperature of 18°C (64.4°F) and a hot climate with an average temperature greater 18°C (64.4°F)[8].

But an average temperature of 18°C or above is great if you want to cultivate mushrooms. So, where is the problem?

The problem is that we are talking about averages over one year. It, therefore, undervalued the high temperature during summer and overvalued the temperature during winter.

We have, thus, take a look at the maximum and minimum temperatures throughout the year (Tab. 2). The average maximum temperature for Darwin, Australia is 30.7 to 33.3 °C (87 to 92 °F).

  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
AVG 31.8 31.5 32.0 32.7 32.1 30.7 30.6 31.4 32.6 33.3 33.3 32.7
MAX 33.4 30.1 34.1 34.5 33.5 33.2 32.6 33.1 34.1 34.8 34.7 34.4
MIN 30.1 29.5 29.7 30.3 30.0 28.7 28.8 29.2 30.6 31.1 31.7 30.8

Table 2: Average, Maximum, and Minimum maximum temperature [°C] in Darwin, Australia, climate zone 1[9]

With a drop in June and July and the hottest month in October and November (Fig. 6).

average maximum temperature for Darwin, Australia

Figure 6: Average Maximum Temperature in Darwin, Australia, climate zone 1[10]

With this foundation about climate zones and the outside conditions, it is time to take a look at the inside or growing conditions.

Definition of the growing condition (inside conditions)

Growing parameters for various mushrooms

Table 3: Growing parameters for various mushrooms[11]

Using the given growing conditions of table 3, we can now define the following range:

Temperature 14 to 23°C (57 to 73 °F)

Based on these values, we now know how much we have to adjust the temperature inside our fruiting chamber. To do so, we subtract the growing temperature from the outside temperature.

Example              35 °C – 15 °C = + 20 °C (+ 36 °F)

Now, after we know the temperature difference, we can go over the different strategies to bring the temperature down. Each one of them helps to reduce the temperature by some degrees.

Use what is available to you and what you need to bring the temperature down.

Strategy 1 – Orientation

The orientation of your (green)house is the main factor when it comes to reducing the heat load within the (green)house itself.

First, look for natural ventilation. Second, orientate long walls to the north and south (Fig. 7).

Perfect orientation of a house

Figure 7: Perfect orientation of a house[12]

Beagley mentioned that avoiding the low morning and afternoon sun is the best way to reduce the inside temperature. This means your house should be facing the short side East and West and not South / North (Fig. 8 and Fig. 9)[13].

Optimal orientation of a house

Figure 8: Optimal orientation of a house[14]

Optimal orientation of a house

Figure 9: Optimal orientation of a house[15]

According to Kumar[16], a single span greenhouse should face east-west, and a multi-span with gutter connected should face north-south for maximum inception of light levels throughout the year. Figure 10 gives us the optimal orientation for a passive solar greenhouse.

Configuration and orientation of a passive solar greenhouse

Figure 10: Configuration and orientation of a passive solar greenhouse[17]

To measure the impact of different greenhouse types on the total radiation intake, the Sethi compared the following greenhouse shapes (Fig. 11) with each other. The results of his test are shown in figure 12.

View of selected greenhouse shapes in E-W orientation

Figure 11: View of selected greenhouse shapes in E-W orientation[18]

According to his findings (Fig. 12), the best shapes to reduce the radiation load are Vinery or Quonset. Or to put it into perspective, if you don’t use these two types, you are getting 7 to 17 percent more solar radiation into your greenhouse and, therefore, a higher heat load.

Availability of total solar radiation for all the shapes at different latitudes in E-W orientation

Figure 12: Availability of total solar radiation for all the shapes at different latitudes in E-W orientation[19]

This results in an increase of about 2.5 to 5°C (4.5 to 9°F) of the inside temperature (Fig. 13).

Hourly variation of greenhouse air temperature (during sunshine hours) for different shapes in E-W orientation during a typical summer day (11-06-07) at 31°N latitude

Figure 13: Hourly variation of greenhouse air temperature (during sunshine hours) for different shapes in E-W orientation during a typical summer day (11-06-07) at 31°N latitude[20]

Conclusion

The preferred shape if the greenhouse is oriented EW is Vinery or Quonset.

Temperature reduction potential             Up to 2.5 to 5 °C or 4.5 to 9 °F

Strategy 2 – Surrounding

After we reduced the temperature through the right orientation and shape of our greenhouse, we can now bring the temperature more down if we design the surrounding of our greenhouse.

To do so, we have several options.

  1. We use passive shading by planting trees and bushes (Fig. 14).
  2. We redirect the cool breeze by guiding it with our plants (Fig. 15).
  3. We block heavy wind through the plants (Fig. 15).
Minimize solar gains with passive shading

Figure 14: Minimize solar gains with passive shading[21]

The practicality of a well-insulated thermal mass for ‘coolth’ storage (Fig. 14) will be addressed in factor 6 (slap vs. open subfloor).

Plant trees and shrubs to funnel breezes

Figure 15: Plant trees and shrubs to funnel breezes[22]

While plants are a natural way to reduce the temperature inside a greenhouse, we can reduce the temperature even further by installing a shade cloth over it (Fig. 16).

Schematic diagram for the greenhouse shaded at different locations

Figure 16: Schematic diagram for the greenhouse shaded at different locations[23]

It could be shown (Tab. 4) that with the right shading, the temperature can be reduced by up to 6°C or 10.8°F (Fig. 17).

Results of the spectro-radiometrical analysis of the experimental materials

Table 4: Results of the spectro-radiometrical analysis of the experimental materials[24]

Diurnal variation of air temperature difference between inside and outside the greenhouse (Tin‐Tout) as affected by the shading configuration

Figure 17: Diurnal variation of air temperature difference between inside and outside the greenhouse (Tin‐Tout) as affected by the shading configuration[25]

Conclusion

External shading reduced the thermal radiation by -21% and -15% day and night.

External shading can be adjusted through the necessary shading factor.

Internal shading increased the thermal radiation inside the greenhouse.

Side-wall shading reduces the transmitted solar radiation in the morning and afternoon (when the outside irradiance is low) and is useless around noon when the outside irradiance is extremely high[26].

Temperature reduction potential             Up to 6°C or 10.8°F

Strategy 3 – Earth-to-air heat exchanger (ETAHE)

The temperature of the earth at a depth of 1.5 to 2 m remains relatively constant throughout the year[27]. This temperature is called the earth’s undisturbed temperature (EUT).

The EUT remains higher than the ambient air temperature in winter and lower than the ambient air temperature in summer[28].

The diameter of the pipe, pipe length, and the number of tubes are the leading parameters to be determined. With an increase in the length of pipe, both pressure drop and thermal performance increase.

A longer pipe of smaller diameter buried at a greater depth and having lower airflow velocity results in an increase in the performance of the EAHE system[29].

There are two different types of ETAHE systems. The first shown in figure 18 and the second one is shown in figure 19.

In the first version, the heat exchange is between the outside and the inside (open loop), while in the second version, the heat exchange is between the inside and the ground underneath the greenhouse (closed-loop).

The only problem with the EAHE systems is that, due to the humid nature of the climate in the rainy season, condensation takes place within the pipes and damages the system[30].

Example of an earth-to-air heat exchanger

Figure 18: Example of an earth-to-air heat exchanger[31]

Pictorial representation of the ETAHE system

Figure 19: Pictorial representation of the ETAHE system[32]

I found on YouTube a very interesting video from someone who is using this method to heat his greenhouse in winter and cool it during the summer.

Conclusion

Installing an ETAHE system underneath the greenhouse can stabilize the temperature throughout the year. In the colder seasons, the temperature will be increased while during the warmer or hotter seasons, the temperature will be lowered.

Temperature reduction potential             Up to 5 to 6 °C or 9 to 10.8 °F

Strategy 4 – (Semi-) Open vs. closed subfloor

As mentioned earlier, the undisturbed ground temperature stays relatively stable throughout the year. The change in temperature from the surface until a depth of 20 ft (6.1 m) can be seen in figure 20.

While during the warmer season, the difference is small, during the wintertime, the temperature at 20 ft (6.1 m) is 15 °F or 8.3 °C warmer than the surface.

This means while the ambient temperature is around 60 °F or 15.5 °C, the ground temperature is at 20 ft or 6.1 m at approximately 77 °F or 25 °C.

monthly undisturbed ground temperature

Figure 20: Monthly undisturbed ground temperature[33]

If the ground temperature is lower than the ambient temperature, consider enclosing subfloors (Fig. 21) [34].

open subfloor vs enclosed subfloor

Figure 21: Open subfloor vs. Enclosed subfloor[35]

The open vs. enclosed subfloor has nothing to do with the open vs. closed greenhouse.

Conclusion

The undisturbed ground temperature can be used to stabilize the temperature inside a greenhouse.

If you’re living in a high humid region, consider an open subfloor to avoid problems with moisture.

Temperature reduction potential             Up to 10 °C or 18 °F (value has to be verified)

Strategy 5 – Slap or open subfloor

If the ground temperature contributes to the heat gain, consider open subfloors otherwise ground-coupled slabs (Fig. 22) [36].

earth coupled slab-on-ground vs open subfloor

Figure 22: Earth coupled slab-on-ground vs. open subfloor[37]

Conclusion

Undisturbed ground temperature can be used to stabilize the temperature inside a greenhouse.

If you’re living in a high humid region, consider an open subfloor to avoid problems with moisture.

Temperature reduction potential             Up to 10 °C or 18 °F (value has to be verified)

Strategy 6 – Open vs. closed greenhouse

While some authors[38] prefer a closed greenhouse, others recommend a semi-open greenhouse[39]. Both are right, but we have to know the context in which each of these greenhouses is used.

If you are running a greenhouse in the Northern Hemisphere, then a closed greenhouse saves you money[40]. But in the regions, I address in this article an open greenhouse is more suitable. Why?

Let’s take a look at the next two figures (23 and 24).

In the first figure, a greenhouse was set up, and the temperature, as well as the humidity during the day, were captured in different locations. At 15h, the temperature at the height of 4.5 m reaches 35°C while the humidity dropped down to about 48%.

It is important to note that at the height of 1.2 m, the temperature inside this greenhouse setting is about 29°C.

Dynamic response of the greenhouse configuration 1

Figure 23: Dynamic response of the greenhouse air temperature and relative humidity for configuration 1[41]

If we compare these numbers with figure 24, we see that at the same time 15h, the temperature is about 25°C and the humidity at 48%.

Same time, different temperatures. In the first configuration, the greenhouse was closed; in the third configuration, the greenhouse used natural and mechanical ventilation to bring the heat down.

What a difference.

Dynamic response of the greenhouse configuration 3

Figure 24: Dynamic response of the greenhouse air temperature and relative humidity for configuration 3[42]

Conclusion

If you run a greenhouse in warmer or even hot climate zones, then an open greenhouse is the way to go.

Temperature reduction potential             Up to 10°C or 18 °F

Strategy 7 – Room height

The height of your greenhouse has a direct impact on the inside temperature.

This effect could be shown in an experiment in which sensors are placed at different heights inside a greenhouse (Fig. 25). The greenhouse had a total height of 5.5 m. The highest placed sensor was at 4.5 m.

Wireless sensor network and horizontal and vertical positions of the sensors

Figure 25: Wireless sensor network and horizontal and vertical positions of the sensors[43]

If we look at figure 26, we see a temperature difference of around 5 °C or 9 °F between the two heights of 2.4 m and 4.5 m.

If, therefore, the greenhouse would have only a height of 2.4 m, we would measure the maximum temperature of 35 °C or 95 °F at that height. This is since warm air rises. This means a higher greenhouse gives the warm/hot air more room to expand and remove it from the crop.

Dynamic response of the greenhouse configuration 1

Figure 26: Dynamic response of the greenhouse air temperature and relative humidity for configuration 1[44]

Conclusion

Increasing the height of the greenhouse reduces the temperature at the crop level by pulling the warm/hot air away from it.

Temperature reduction potential             Up to 5 °C or 9 °F

Strategy 8 – Insulation

Sound insulation of the building helps to reduce the overall temperature swing inside it. To see the difference between a construction with no insulation and with insulation, let’s look at the following to figures (27 and 28).

In the first graph, we that the inside temperature rises almost at the same rate as the outside temperature increases. This is in stark contrast to the insulated building (Fig. 28).

Correlation between inside and outside temperature swing for a building with no wall insulation, timber floors and brick

Figure 27: Correlation between inside and outside temperature swing for a building with no wall insulation, timber floors and brick[45]                                                       

Here the rate is cut down roughly in half.

Correlation between inside and outside temperature swing for a building with no wall insulation, concrete slab and brick

Figure 28: Correlation between inside and outside temperature swing for a building with no wall insulation, concrete slab and brick[46]

Here are some recommendations I found in one of the articles:

“In climates that require only cooling or those with limited cooling needs, use multiple layers of reflective foil insulation in the roof instead of bulk insulation […]

Zone 1                  add bulk insulation around the room(s)

Zone 2                  Use bulk and/or reflective insulation to prevent heat loss and heat gain.

Zone 3                  High insulation prevents winter heat loss and summer heat gain.

Zone 4                  not mentioned in the article[47].”

Conclusion

Proper insulation helps to reduce the necessary cooling. But on the other side, the investment cost will increase. Therefore, there will be a tradeoff between the investment costs and the cost of cooling, which depends on the situation you are in.

Temperature reduction potential             Depends on the material you’re using.

Strategy 9 – False wall/ceiling

False wall

A false wall is an easy way to reduce the heat load of the building and can be installed on an existing building. A simple false wall consists of a metal cladding (Fig. 29), which is mounted with an air gap to the wall.

The colder air will enter the false wall at the bottom, rise behind the false wall due to the chimney effect, and will leave the false wall at the top.

By doing so, it provides insulation to the building and, therefore, reducing the heat load.

Example of a false wall

Figure 29: Example of a false wall[48]

False ceiling

Another strategy to reduce the heat load within a building is the use of a false ceiling. In a study, the author analyzed a building with a flat concrete roof with and without a false ceiling.

The temperature with the false ceiling could be dropped down from around 44 °C (111 °F) to 30 °C (86 °F) inside.

Variation of temperatures with time for the first (no FC) and second (with FC) cases of the model

Figure 30: Variation of temperatures with time for the first (no FC) and second (with FC) cases of the model[49]

Conclusion

False walls and or false ceilings are a good way to reduce the overall heat within a greenhouse.

Temperature reduction potential         Up to 4 °C or 7.2 °F (false wall); If the effect is similar to a solar chimney

Up to 14 °C or 25.2 °F (false ceiling)

Strategy 10 – Solar chimney

Solar chimneys are a good way to reduce the heat inside a (green)house. The first option is to cool the roof (Fig. 31), the second option to cool the room (Fig. 32).

Example of a solar chimney – roof ventilation

Figure 31: Example of a solar chimney – roof ventilation[50]

Example of a solar chimney – room ventilation

Figure 32: Example of a solar chimney – room ventilation[51]

One author compared different settings (number of solar chimneys) in different ambient air temperatures (Fig. 33).

System performance at different indoor and outdoor conditions

Figure 33: System performance at different indoor and outdoor conditions[52]

To achieve the best results a tilt angle of 60 ° is recommended (Fig. 34)[53].

Average performance comparative function for June, July, August and whole summer

Figure 34: Average performance comparative function for June, July, August and whole summer[54]

Conclusion

Solar chimneys alone or in conjunction with an earth-to-air heat exchanger are a good solution when it comes to cooling your fruiting chamber.

Temperature reduction potential             10 °C or 18 °F coupled with an EATHE

4 to 5 °C or 7.2 to 9 °F alone (EATHE provides 5 to 6 °C or 9 °F 10.8 °F of cooling)

Strategy 11 – Color of walls/cladding/roof

Any walls exposed to sunlight need to be a light color to reduce the heat absorption[55]”.  Or to paraphrase it differently. The darker the color the more heat will be absorbed which is indicated by the absorptance factor (Tab. 5).

K-Solar Absorptance for different colors

Table 5: K-Solar Absorptance for different colors[56]

How these numbers translate into heating and cooling can be seen in figure 35. The figure clearly shows that the higher the factor, the more cooling is needed and vice versa.

Solar absorption coefficient vs heating and cooling energy consumption

Figure 35: Solar absorption coefficient vs heating and cooling energy consumption[57]

To understand figure 35 even better, let’s take a look at the following graph (Fig. 36). The graph shows the correlation between the total solar reflectance and temperature increase.

Experimental correlation between TRS value and heat build-up

Figure 36: Experimental correlation between TRS value and heat build-up[58]

The more of the incoming radiation is reflected, the less heat will be absorbed. This correlation is shown in figure 37. 

Definition of reflection, absorption, and transmission

Figure 37: Definition of reflection, absorption, and transmission[59]

Between the two colors white (titanium oxide) and the black (carbon black) lies a factor of 2 or to be more practical, a delta of 25 °C (45 °F).

Conclusion

The color of the roof, walls, and cladding have a significant impact on the overall heat load of the building. The lighter the color, the less cooling is needed.

Temperature reduction potential             Up to 25 °C or 45 °F (in relation to black)

Strategy 12 – Ventilation capacity

The idea of using natural ventilation as a means to reduce the inside temperature can be found in many countries. In Iran, for example, they developed the so-called “WindcatchersYazd (Fig. 38).

Typical Iranian badgir

Figure 38: Typical Iranian badgir[60]

The next figure (39) shows a section of the badgir and the airflow throughout the building. The idea here is that the incoming air is forced down the tower, passing through the building and taking the heat with it when leaving the building through openings on the other side.

Section of a badgir

Figure 39: Section of a badgir[61]

The ventilation capacity strongly influences the inside temperature[62]. This means everything which blocks the airflow will lower the ventilation capacity. In regard to mushroom production, we have to think about the flyscreens we put in place.

Flyscreens help to control insects but do restrict the airflow[63]. The ventilation capacity without insect net should be, therefore, greater than 30 % and with insect nets greater 40 %[64].

While the standard procedure for greenhouses is to open the sidewalls, some author suggests that the ventilation should be done through opening the short sides of the greenhouse (fly screen) and the roof (fly screen) with a ventilator[65] (solar chimney) in the roof.

If we take both ideas together, we will end up with something which looks like the following figure (40).

New fruiting chamber design with wind catcher and solar chimney

Figure 40: New fruiting chamber design with windcatcher and solar chimney[66]

The new fruiting chamber design would use the natural forces caused by the pressure differences to cool itself. The advantage of this new design is that it should work in low wind/hot areas as well.

This idea is not new. Bansal analyzed the combination of a wind tower – solar chimney system[67].

He found that the combination would increase the airflow from 0.75 kg/s up to 1.4 kg/s at 700 W/m²[68] and a wind speed of 1.0 m/s.

As Impron[69] wrote, “A high ventilation capacity tends to make the climate between outdoor and indoor highly coupled, showing that passive control of greenhouse climate by natural ventilation can avoid a significant increase in TAir.”

Conclusion

Using natural ventilation to reduce the inside temperature is worth considering. Mainly because it is cheaper than using forced ventilation. The combination of a wind catcher and a solar chimney increases the airflow within the building and, therefore, reduces the overall temperature.

Temperature reduction potential             Up to 4 to 5 °C or 7.2 to 9 °F (solar chimney alone)

No values for the combination (it has to be tested).

Strategy 13 – Cooling (active vs. passive)

Only after we set a good foundation by applying all the strategies above, we start thinking about the cooling method.

Because, if we did a good job, there is almost nothing to cool off.

But let’s look at how you can reduce the temperature within a greenhouse be using the right cooling method.

Ventilation method

The first method is using fresh air, which we redirected through plants (strategy 1). The author of the next study analyzed different ventilation strategies. He used the following greenhouse design (Fig. 41).

Cross-section of the greenhouse

Figure 41: Cross-section of the greenhouse[70]

And the following ventilation methods (Tab. 6).

Scenario AO WC LC
Side vent Open Open Open
Roof Windward vent Open Closed Open
Roof Leeward vent Open Open Close

Table 6: Ventilation methods[71]

As figure 42 clearly shows, scenario WC resulted in a lower temperature inside the greenhouse. In this graph, the temperature goes from 32.5 °C (red) to 22.0 °C (blue). With scenario WC the inside of the greenhouse is a mixture of blue and green while in the other scenarios green and even yellow or red is present.

Temperature contour and air velocity vectors in transient analysis for the three scenarios at 2400s

Figure 42: Temperature contour and air velocity vectors in transient analysis for the three scenarios at 2400s[72]

As the above figure is the result of a simulation, we can stop it at any time and look at the temperature at different heights (Fig. xx). The chart (Fig. 43) shows these different temperatures at a height of 1.5 m and after 60 min of ventilation.

With the WC scenario, the temperature could be lowered by 3.5 °C or 6.3 °F.

Horizontal temperature profile at height of 1.5 m for the three scenarios at 60 min

Figure 43: Horizontal temperature profile at height of 1.5 m for the three scenarios at 60 min[73]

If we take a look at the next figure (44), we see that the third option lowered the temperature faster than the other two. For me, that would be a good starting point. Which means, I would first use configuration 3 (LC) and then after 500 s switching to configuration 2 (WC).

In this case, I can benefit from both scenarios. First, rapid cooling and second, the best cooling out of the three configurations.

Mean temperature trends in the cultivation area for the three opening configurations considered

Figure 44: Mean temperature trends in the cultivation area for the three opening configurations considered[74]

For greenhouses in tropical lowland, it is recommended to keep the ratio of the opening to floor greater than 60 %[75]. This allows us to maintain the temperature inside the greenhouse near the outside temperature.

  • The higher the wind speed, the higher the ventilation rate[76].
  • The larger the floor area, the lower the ventilation rate[77].

Evaporating Cooling

The most common method of evaporating cooling is the use of a pad system (Fig. 45). Here the water flows from top to bottom while air flows from outside through the cooling pad towards the crop by using fans.

Movable evaporative cooling pads

Figure 45: Movable evaporative cooling pads[78]

By using these systems, the temperature can be reduced (Fig. 46). Unfortunately, this reduction is not homogenous throughout the greenhouse. The further away from the cooling pad, the higher the temperature rises (Fig. 46).

This leads to a temperature gradient throughout the greenhouse of roughly 10 °C or 18 °F.

Temperature gradient inside the greenhouse

Figure 46: Temperature gradient inside the greenhouse[79]

Sprinkling on the roof

Studies showed that by sprinkling water on the roof, the water film evaporates and, therefore, reduces the temperature inside the greenhouse[80].

Figure 47 shows an example of this method. Here nozzles are placed above a second canopy and sprinkling water on it. By doing so, a thin water film is formed. Due to the evaporation of the water, the greenhouse gets cold.

Geometries of three different configurations tested for the natural ventilation

Figure 47: Geometries of three different configurations tested for natural ventilation[81]

In another test done by the same author, it could be shown that up to 13 °C or 23.4 °F temperature difference could be achieved with such a system (Fig. 48).

Test results of the NVAC cooling system

Figure 48: Test results of the NVAC cooling system (blue: outside conditions, orange: initial conditions, grey: NVAC conditions; green: difference between initial and NVAC conditions)[82]

Conclusion

All three cooling methods showed that a decrease in temperature is feasible.

Cooling method Temperature reduction potential (up to …)
Ventilation 3.5 °C or 6.3 °F
Evaporating cooling 3 °C or 5.4 °F
Sprinkling on the roof 3 to 6 °C or 5.4 to 10.8 °F

Strategy 14 – Heating (active vs. passive)

I know this strategy has nothing to do with cooling, but as there are regions with a dry summer and a cold winter (zone 4), we have, therefore, to talk about heating as well. In the following sections, I will give you a brief overview of 6 ways to heat your fruiting chamber.

Passive heating via

  • Water storage

One way of heating your fruiting chamber, aka greenhouse, is by using water storage as heat storage. This storage can be placed inside or outside of the room. If you place it outside, you need a heat-transfer fluid.

The storage itself can be made of plastic bags (Fig. 49) or containers (Fig. 50).

Heating via Water storage in plastic bags

Figure 49: Water storage in plastic bags[83]

Heating via water storage in containers

Figure 50: Water storage in containers[84] 

Temperature increasing potential            2-10°C higher than the ambient temperature

  • Latent heat storage

Another way to heat the room is the use of a liquid called chliarolithe-CaCl2 6 H2O, which has a melting temperature of 25°C and a latent heat of 154,900 kJ/m³.

The heat storage is placed underground, on a well-insulated area, or at the north sidewall.

Unfortunately, the latent heat material must be replaced every 1-2 years!

Heating via latent heat storage material

Figure 51: PSG with latent heat storage material[85]

Temperature increasing potential            no data available

  • Rock bed storage

An alternative solution to the liquid is the use of a rock bed as storage. The storage area is placed under the greenhouse at a depth varying between 40 and 50 cm.

Heating via rock bed storage

Figure 52: PSG with rock bed storage[86]

Temperature increasing potential            4-20°C higher than the minimum ambient air temperature

  • Soil storage with buried pipes (EATHE)

I described this method in strategy 4 but under the aspect of cooling. As mentioned, the soil temperature remains 2-3°C higher than the winter ambient air temperature, in depths only a few meters from the ground surface. 

Heating via buried pipes

Figure 53: PSG with buried pipes[87]

The warm air gives up its heat content to the pipe by condensation, where it is stored in the form of latent heat for up to 10-12 hours. The tubes are buried at a depth of 1.5 m.

Temperature increasing potential            2-4°C higher than the minimum outside air temperature

  • Other types of heat storage

A variation of the water container storage is the north storage wall. It is externally insulated and internally painted black. It is usually 60 cm or 24 in thick.

Heating via north wall storage

Figure 54: PSG with north wall storage[88]

Temperature increasing potential            1-20°C higher than the minimum outdoor air temperature.

Conclusion

It could be shown that passive heating is possible and provides a good alternative to other heat sources.

Temperature increasing potential            Up to 20 °C or 36 °F

Recommendation to Reduce the Heat inside the Greenhouse

The following recommendations in table 7 are the summary of the article.

If you just jumped here to get an idea I recommend that you go to the specific section an read more about the strategy you want to apply.

  Zone 1 Zone 2 Zone 3 Zone 4 Temperature reduction potential (up to …)
               Def.  


Strategies
High Humid Summer Warm Winter Warm Humid Summer Mild Winter Hot Dry Summer Warm Winter Hot Dry Summer Cold Winter
Orientation Short side to the south/north Short side to the south/north Short side to the south/north Short side to the south/north 2.5 to 5°C 4.5 to 9°F
Shape Vinery or Quonset Vinery or Quonset Vinery or Quonset Vinery or Quonset
Surrounding Trees south side Guiding the breeze Trees south side Guiding the breeze Trees south side/guiding the breeze, waterfront Trees south side/guiding the breeze, waterfront 6°C
10.8°F
Shading Yes (outside) Yes (outside) Yes (outside) Yes (outside)
Shading color Black Black Black Black
ETAHE Yes
With drainage
Yes
With drainage
Yes Yes 5 to 6 °C
9 to 10.8 °F
Semi-open vs. closed slap floor Semi-Closed Semi-Closed Open Closed 10°C
18 °F (?)
Slap vs. open Slap Open Open Slap
Open vs closed greenhouse Open Open Open Open 10 °C 18 °F
Room height 4 m (ft.) 4 m (ft.) 4 m (ft.) 4 m (ft.) 5 °C
9 °C
Insulation Yes Yes Yes Yes  
False wall Yes Yes Yes Yes 4 °C
7.2 °F
Solar chimney Yes Yes Yes Yes 10 °C
18 °F (coupled with ETAHE)
Ventilation capacity > 30 % no nets
> 40 % with nets
> 30 % no nets
> 40 % with nets
> 30 % no nets
> 40 % with nets
> 30 % no nets
> 40 % with nets
4 °C
7.2 °F (with solar chimney
Vent opening/floor ratio > 60 % > 60 % > 20 % > 20 % 1 to 2 °C
1.8 to 3.6 °F
Color of walls/cladding/roof Light color Light color Light color Light color 25 °C 45 °C (in relation to black)
Cooling Natural Ventilation Natural Ventilation Natural Ventilation plus Evaporating and roof sprinkling Natural Ventilation plus Evaporating and roof sprinkling 3.5 °C 6.3 °F  
3 to 5 °C 5.4 to 9 °F
Heating (during winter) No Yes or No depending on the winter No Yes heating potential up to 20 °C or 36 °F higher than ambient air
Construction Low thermal mass Low thermal mass (mild winter) High thermal mass (cold winter) High thermal mass High thermal mass  

Table 7: Summary of the recommendations to reduce heat inside the greenhouse for the zone 1 to zone 4; temperature reduction potential in regards to the reference values mentioned in the literature; text in red: parameters have to be verified[89]

Final Words

As shown in this article there are many strategies to lower the temperature inside your fruiting chamber.

If you want to dive deeper into a specific topic I put all the used literature in the next section.

Now I want to hear from you:

Which technique from this post are you most excited to try? Which technique do you currently use?

Let me know by leaving a quick comment.

Literature

Bureau of Meteorology, Australian Government

http://www.bom.gov.au/climate/data/index.shtml

Paul Stamets 1983

The Mushroom Cultivator https://amzn.to/2WRaR4v

Beagley 2011

http://coolmob.org/wp-content/uploads/2014/04/COOLmob_Design_Booklet.pdf

Hasan

https://www.sciencedirect.com/science/article/pii/S0196890408001751

Kumar 2009

https://www.sciencedirect.com/science/article/abs/pii/S0378778809001844

GERES 2004

http://www.solaripedia.com/files/1086.pdf (PDF)

Sethi 2009

https://www.sciencedirect.com/science/article/pii/S0038092X08001540

YourHome

https://www.yourhome.gov.au/passive-design/passive-cooling

Abdel-Ghany 2015

https://www.researchgate.net/publication/286418533_Radiometric_Characterization_Solar_and_Thermal_Radiation_in_a_Greenhouse_as_Affected_by_Shading_Configuration_in_an_Arid_Climate

Trilok 2015

https://link.springer.com/article/10.1186/s40517-015-0036-2

Sobti 2015

https://link.springer.com/article/10.1186/s40517-015-0034-4

Parker 2016

http://fsec.ucf.edu/en/publications/pdf/FSEC-CR-2042-16.pdf (PDF)

Lee 2010 https://etd.ohiolink.edu/!etd.send_file?accession=osu1274996517&disposition=attachment (PDF)

Zorzeto 2014

http://www.ipcbee.com/vol79/008-ICABT2014-L0026.pdf (PDF)

Baggs 2006

https://www.academia.edu/9106613/Ther_mal_Mass_in_Building_Design (PDF)

Razek 2014

https://www.researchgate.net/publication/282660536_THE_EFFECT_OF_USING_FALSE_CEILING_ON_ROOF_COOLING_LOAD?enrichId=rgreq-5baeba8108402b17203e17a1d164baba-XXX&enrichSource=Y292ZXJQYWdlOzI4MjY2MDUzNjtBUzoyODIzMDg0MjM3NjYwMTdAMTQ0NDMxODk4MTY1Mw%3D%3D&el=1_x_3&_esc=publicationCoverPdf

Maerefat 2010

https://www.sciencedirect.com/science/article/pii/S0960148110001059

Hamdy 1994

https://www.sciencedirect.com/science/article/pii/S0960148198000937

Passive Solar Industries Council

https://www.nrel.gov/docs/legosti/old/17252.pdf (PDF)

Yao 2011

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.891.2089&rep=rep1&type=pdf (PDF)

BASF

https://www.dispersions-pigments.basf.com/portal/streamer?fid=560474 (PDF)

El-Borombaly 2015

https://www.researchgate.net/publication/281282008_Adaptation_of_Vernacular_Designs_for_Contemporary_Sustainable_Architecture_in_Middle_East_and_Neotropical_region?enrichId=rgreq-12441a5be93b50e90918cced67ee9819-XXX&enrichSource=Y292ZXJQYWdlOzI4MTI4MjAwODtBUzoyNjc3NDUwNTcwNDY1OTFAMTQ0MDg0NjgwNTAzMQ%3D%3D&el=1_x_3&_esc=publicationCoverPdf

Champen 2005

https://www.ishs.org/ishs-article/691_50

Elings no Date

http://www.fftc.agnet.org/library.php?func=view&style=type&id=20180518105801

Bansal 1994

https://www.sciencedirect.com/science/article/pii/0360132394900086

Impron 2011

https://www.semanticscholar.org/paper/A-greenhouse-crop-production-system-for-tropical-Impron/c256f320b25a2f06b0775f3456e5318c94a21d78

Benni 2016

https://www.sciencedirect.com/science/article/pii/S0378778816303759

Perret 2005

https://www.researchgate.net/publication/228551655_HUMIDIFICATION-DEHUMIDIFICATION_SYSTEM_IN_A_GREENHOUSE_FOR_SUSTAINABLE_CROP_PRODUCTION

Yongxin 2002

http://www.paper.edu.cn/scholar/showpdf/MUT2ENwIMTj0Mxyh

Li 2018

https://www.researchgate.net/publication/326559118_Factors_affecting_greenhouse_microclimate_and_its_regulating_techniques_A_review

McCartney 2017

https://pdfs.semanticscholar.org/92da/ec60101250fbc0f43f97a8349095a35d745b.pdf (PDF)

Santamouris 1994

https://www.researchgate.net/publication/223451658_Passive_solar_agricultural_greenhouses_A_worldwide_classification_and_evaluation_of_technologies_and_systems_used_for_heating_purposes


[1] If they are edible. Be aware that there are poisonous mushrooms out there!

[2] abcb.gov.au

[3] basc.pnnl.gov

[4] Source (pdf)

[5] Own table

[6] Own figure based on Bureau of Meteorology, Australian Government

[7] Own figure based on Bureau of Meteorology, Australian Government

[8] Source

[9] Own figure based on Bureau of Meteorology, Australian Government

[10] Own figure based on Bureau of Meteorology, Australian Government

[11] Own table based on Stamets 1983

[12] Beagley 2011

[13] Beagley 2011

[14] Beagley 2011

[15] Hasan

[16] Kumar 2009

[17] GERES 2004

[18] Sethi 2009

[19] Sethi 2009

[20] Sethi 2009

[21] YourHome

[22] YourHome

[23] Abdel-Ghany 2015

[24] Abdel-Ghany 2015

[25] Abdel-Ghany 2015

[26] Abdel-Ghany 2015

[27] Trilok 2015

[28] Trilok 2015

[29] Trilok 2015

[30] Sobti 2015

[31] YourHome

[32] Sobti 2015

[33] Own figure based on Parker 2016

[34] YourHome

[35] YourHome

[36] YourHome

[37] YourHome

[38] Lee 2010

[39] Zorzeto 2014

[40] Lee 2010

[41] Zorzeto 2014

[42] Zorzeto 2014

[43] Zorzeto 2014

[44] Zorzeto 2014

[45] Baggs 2006

[46] Baggs 2006

[47] YourHome

[48] Beagley 2011

[49] Razek 2014

[50] YourHome

[51] YourHome

[52] Maerefat 2010

[53] Hamdy 1994

[54] Hamdy 1994

[55] Beagley 2011

[56] Passive Solar Industries Council

[57] Yao 2011

[58] BASF

[59] Own figure

[60] El-Borombaly 2015

[61] El-Borombaly 2015

[62] Champen 2005

[63] Beagley 2011

[64] Elings n.D.

[65] GERES 2004

[66] Own figure based on Bansal 1994

[67] Bansal 1994

[68] Bansal 1994

[69] Impron 2011

[70] Benni 2016

[71] Benni 2016

[72] Benni 2016

[73] Benni 2016

[74] Benni 2016

[75] Impron 2011

[76] Impron 2011

[77] Impron 2011

[78] Perret 2005

[79] Perret 2005

[80] Yongxin 2002, Li 2018

[81] McCartney 2017

[82] Own figure based on McCartney 2017

[83] Santamouris 1994

[84] Santamouris 1994

[85] Santamouris 1994

[86] Santamouris 1994

[87] Santamouris 1994

[88] Santamouris 1994

[89] Own table based on all the finding

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