A little concern about extravagant cooling costs and overheating of a metal shipping container home is completely understandable. The key to getting a comfortable temperature within your shipping container home is simply to keep the heat out by planning for it before the conversion process starts.
The Sun and ambient air are the two major agents of heat for your container home. To keep the home cool, we need to manage the effect of these two on the container first, and then insulate the container and add HVAC for further control. The table below indicates some of the ways to manipulate the two agents to your advantage to reduce your cooling load.
|Factor||To keep it cool|
|1||Orientation||Longer side away from the south.|
|2||Exposure to direct sun||Shading using overhangs, or oversized roof|
|3||Type of glass used||Glass with minimum heat transfer ( lower U value)|
|4||Site development||Landscape, water bodies along the wind direction|
|5||Insulation used||Highest R-value (depends on location)|
|6||Colour on the exterior||Light-coloured walls and roof, to reflect sun’s radiation|
|7||Roof treatment||Reflective paints or coatings.|
This article will elaborate on the aforementioned factors and help you to implement them correctly in your location. Keep reading to find some effective insulation and roof treatment types as well.
There are several passive and active ways that a shipping container home can be designed to reduce the load on your air conditioner and, ultimately, your pocket. Let’s dive into them in detail below.
· With respect to Sun
The modular rectangular quality of the shipping container makes this decision very easy. The sun essentially moves from east to west through the south. This means that our buildings are exposed to solar radiation from the south throughout the day, whereas east and west become indirect light zones in some parts of the day. Orienting your container home such that the longer side of the container is not exposed to day-long south radiation will effectively help reduce heat absorption and thus reduce the heating.
Also, if possible, plan the bedroom/ less occupied space towards the southern wall, as it is used mostly at night when the sun’s radiation is not a factor to worry about. Given the linear nature of a shipping container, this would be fairly easy to achieve.
However, despite these standards, make sure to observe the real south of your site and place it accordingly.
· With respect to wind
Every place has a wind pattern. Even though the wind directions keep changing throughout the year, analysing the prominent wind direction in summers can help you plan your home for cross ventilation, especially if you reside in a humid climate. With the vast satellite generated data on the internet, this would be fairly easy to find.
The major source of heat for any home is SUN. Metal actively absorbs the sun’s radiation and can get hotter than the ambient air, ultimately converting the inside into a hot oven. Protecting your shipping container from the sun’s rays can bring down the temperature by almost 20 degrees.
There are two ways to achieve this, based on your surroundings, site and budget.
- Building a secondary roof over the container home that extends beyond the container on all four sides. The roof shall block the sun’s radiation and thus reduce heating to some extent.
- Surrounding the container by tall shading trees: Surrounding by trees gives an added benefit of cooling the ambient air, which shall further help in reducing the ambient temperature.
- Thick-dark coloured curtains on the windows which get direct sun. These curtains act as a barrier for the sun’s radiation to directly enter the space through windows, therefore, reducing the heat to some extent. (post-conversion)
Doors and Windows
The goal when selecting the glazings in the house is:
Light in -> Heat out
Glass is a complicated material. Even though it is a bad conductor, it has a high capacity to absorb and transfer radiation and heat inside your home. Have you ever noticed that the air near your window on a hot day is significantly hotter? If not chosen carefully, it can substantially reduce the performance of your insulation. There are plenty of ways to ensure that doesn’t happen, and you can still incorporate large full height fenestrations into your home without any worries.
- Low E glass/ Low E films: Low E Glass stands for Low emissivity glass. Such windows have a coating that prevents UV and IR (Infrared) radiations to pass through them while allowing the majority of visible light. Controlling and blocking these radiations lessens the passage of heat through your window.
The best part is, if you’ve already installed your windows, you can still apply Low E Films on your existing window. They are also very effective and easy to apply. (post-conversion)
- DGU and TGU Windows: The DGU and TGU stand for double glazed units and triple glazed units. These windows comprise two and three layers of glass, with inert gasses like Argon between them. The multiple layers and the inert gas prevent heat transfer through the glass and allow maximum natural light. These windows are very effective in lowering the cooling loads and controlling the temperature.
- Understanding the standards– Three factors indicate the heat prevention performance of your window.
- U- Value: The lower the U value, the better the heat resistance.
- Solar Heat Gain coefficient (SHGC)– Te lower the SHGC value, the better
- Visible Transmittance (VT)- The higher the VT, the better performance.
The best way to keep cool within a space is to ensure the flow of air. If the hot air can escape and new air can enter the space, the temperature control will be more effective. An HVAC system does just that. It takes out the hot air and introduces the cooled air continuously.
If you intend to be energy efficient, you must introduce cross ventilation in your spaces so that you don’t need to use the energy-hungry HVAC throughout the day, but just at the hottest times.
- Install exhaust fans on both smaller ends of the container, which will allow your home to pull fresh air from the outside and eliminate the hot stale air, in summers (hot air rises), for non-extreme times.
- Plan your windows carefully, ensuring enough cross ventilation. Some vents at the top could allow the hot air to escape easily, maintaining the temperature within as Hot air rises. (The design of this, of course, may vary if you plan to seal the room for air conditioning.)
- Night cooling– As the sun sets, it takes its radiation away with it. Thus, the nights tend to be cooler and, hence, can withdraw heat out of your home. Night cooling works when the windows and fenestrations are opened at night to allow the hot air to escape, and then close them right before the sun rises to prevent heating again. This method can significantly control indoor temperature. Of (Of course, this is effective only if you are an early riser!)
These tricks might not be the best if you reside in a hot and humid environment, but for an arid and hot and dry region, this is a lifeline—both for eyes and body.
Site development has a major role in passive cooling. If you have the resources, site and budget, investing in it pays off in the long term. Surrounding your home with some native plant species allows them to cool the air that enters your home when it passes through their perspiring leaves. They also provide a good shade from the sun and filter its radiation before it enters the home.
Moreover, introducing a small pond, fountain or swimming pool in the landscape, along the prominent wind direction, can significantly lower the temperature of ambient air that enters your home.
As discussed above, the sun’s radiation is the major source of heat for a container home. Therefore, reducing the ability of the roof of the container to absorb the heat from these radiations shall significantly affect the heat transfer.
Today, there are various kinds of roof treatments and coatings available in the market. Generally, if the roof is painted white, it can reflect most of the radiation and prevent the interior from heating up. But white paint is not the most durable, and therefore effective only for a short time.
These reflective coatings are wear resistant and more viscous, thus are more durable. These have certain particles that reflect the sun’s heat radiations and provide the added benefit of using a range of colours for aesthetics instead of just white. Thus, investing in it is the right choice. (post-conversion)
However, if you build an oversized roof over your container, this step can be eliminated, as there is no direct sun to reflect anymore.
Major types of reflective coatings available in the market include:
- Acrylic roof coating- These are effective and economical coatings and can reduce temperatures by 20 degrees. But here are some drawbacks
- It weathers and becomes thinner at very high temperatures.
- Not ponding proof
- High cure time- need to be protected by water or snow during the curing period
- Silicone roof coating- This one is also an effective option. It is weather and wear-resistant, allows ponding water, and has a lesser curing time. However, it has some drawbacks
- It is Expensive
- Holds dirt on the surface, thus can reduce reflectivity
- Installation requirements are a little complicated.
- Polyurethane coatings- These offer the best impact/ weather resistance and high reflectivity. They come in two types, aliphatic and aromatic. These are typically used in combination as a base and topcoat. Aromatic is the base coat for its durability but has low UV resistance, and aliphatic is the topcoat for its UV resistance and stays clean and longer. Its drawbacks are:
- It is Expensive
These coatings are easy to apply. Its application process is very similar to paint.
Since the shipping container is a metal box, insulation remains the key to a reduced cooling load and energy bills even if you do all the above steps. Insulating a shipping container is easy but needs efficient installation and a good investment. Don’t wait or cut off in this process. There are various types of insulation available in the market. The performance of insulation is judged by the R-value it offers. Even though that is not always accurate, because the performance can be hindered by the air gaps, fluff and improper installation of the insulation, but R-value is the only standard available. The higher the R-value, the better. Of course, this decision depends on your location and the highest temperatures.
There are a few aspects to consider while deciding on the insulation for your shipping container home.
- The R-value- The R-value depends on thickness, density and type of insulation. However, It is crucial to retain the value of any insulation for it to work effectively. In many cases, improper installation, compression or thermal bridging can lead to an undesirable heat transfer, affecting the insulation and air conditioning performance.
- Space within your container- Most bat insulations such as glass fibre, stone wool etc., occupy a thicker part of the wall section, as their performance is based on the air gaps within them. Compressing them can reduce their R-value greatly. It can also lead to a loss of almost 12 inches, including the covering and drywall in your narrow 8 ft wide shipping container. So, thinner but effective options need to be explored.
- Condensation- As the temperature of the metal walls is very high compared to the insulation, condensation is a common threat in shipping containers. In such cases, with normal bat or roll insulation, another layer of vapour retarder will be needed, which is an added expense.
Pertaining to all these factors, the closed-cell spray foam is the best kind of insulation, as it has the highest R-value, requires less space, and works as a vapour retarder as well. It gives a per inch value of R-7 if installed correctly, compared to R- 3. To R 3.5 / inch of most other types of bat insulation.
All these methods mentioned above are effective but need to be planned before beginning the conversion of your shipping container home. These factors will have a big chunk on your bills, but these are the things that will ensure that your shipping container home is comfortable without ripping you off on energy bills later.