Choosing the Right Solar Heating- Passive, Active & Open Loop


Solar heating system is a device that collects heat from solar energy and supplying our home with hot water. The device is eco-friendly and also an excellent option for us to reduce heating cost.

Basically, there are many types and options of solar water heating system that available in the market today. Perhaps the variety of types and options make us confuse and difficult to choose. In this article we shall discuss on some basic concept of how it work, their benefits and also some complications of the system. Later in the next coming articles we shall go further on other types of the solar heating system.

Good Solar Location

Solar insolation map

Solar insolation map

The main criterion for solar heating installation is your location. A location is consider a good location if it receives good solar energy that is enough to produce heat for the system to work. Fortunately, most parts of the world are potential for good installation.

Below are few free references that available on internet from governmental websites. We cannot find much free information to list it here. Readers also could obtain information in your country from governmental departments or maybe universities. Further you could also find paid information that available on internet not free but extremely accurate with current data.

 Renewable Energy Incentives

Many governments worldwide provide special incentives for renewable energy installation. Here are incentives for the United States and the United Kingdom.

Open Loop and Passive System

Sometimes it is called thermosyphon

Sometimes it is called thermosyphon

Open loop system or also known as direct system is the simplest solar water heater system that available in the market. It uses flat-plate solar collector. The system is not as efficient as the others, however very reliable because of less components and last longer. The system is named open loop because the water is openly flows from our home to the system in and out.

The system is suitable for any climates; however during freezing temperature water inside the system could freeze and damage the system parts. The main reason is water expands its volume when become ice.

Water in a collector which is open to a clear sky can freeze when the ambient air temperature reach 40 degrees Fahrenheit or 4-5 degree Celsius. This situation is called night sky radiation. For cold climate application, the best practice is to use only in three seasons or two seasons depends on your climate behaviours. Stop using the system during winter or cold time by drain all the water from the system.

Open loop system has two variations either to use a pump or without a pump. The system which has no pump is called passive system because it has no other components that move water inside the system.  It works entirely by thermosyphon or liquid convective heat transfer. The cold water moves naturally towards hot water (or solar collector) to reach equilibrium. The process works continuously as long as water inside the solar collector is warmer than the cold water.

Open loop and passive is a good option because you don’t need to waste electricity for the pump. You just need to be careful with the ambient temperature so that it won’t reach 40 degrees Fahrenheit or 4-5 degree Celsius. Nevertheless, there is one disadvantage of the passive system which is the tank is located at the top of the solar collector and install outside your home. The chances of heat loss are possibly larger than if it is being installed inside our home.

Open loop, passive solar heating system

Open loop, passive solar heating system

Open Loop and Active System

Active system is more costly than the passive system because it incorporates pump, controller, sensor and other options such as drain back tank. Some system offers even solar PV to power the pump, controller and other electronics parts in the system.

Although it is more expensive, however it has a number of benefits such as it could be integrated with backup gas or electric heater. The system also has wide ranges of smart mechanisms because the system is driven by electronics.

The system is more efficient than the passive system because it is controlled by electronics. However it’s very difficult to judge totally whether this system is better than the passive one because it’s depend on your climate and applications.

Open loop, active solar heating system

Open loop, active solar heating system

2nd Part: Choosing the Right Solar Heating- ICS & Close Loop Basics

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One thought on “Choosing the Right Solar Heating- Passive, Active & Open Loop

  1. This system looks really nice. I’m all for finding ways to lower our energy bills and sticking it to the man. Thank you for those links because I was able to see if my state is a good enough place to get solar.

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