Hot Gas defrost system
Hot Gas defrost system
All freezer systems form ice on the evaporators and occasionally require some form of defrost. Electric defrost systems with electric resistance heater elements are very popular because of their relative easiness. However, electric resistance heat uses a more of energy. Some systems are intended to use hot discharge gas from the compressor to defrost evaporators and accomplish the task much more efficiently than electric resistance heaters. Hot gas defrosting uses less energy because it is takes less energy to transfer heat than it does to create heat.
The Hot Gas Defrost process uses the superheated vapour from the compressor release (on high pressure and high temperature) as the heat source. This vapour is distracted on a third system line, bypassing the condenser and the increase valve, directed through the unit cooler coil, warming it from the inside.
The main benefit of this process is the energy saving component. Since the entire coil warms up, about 70% of the heat from the hot gas is fixed to the ice block, exit only 30% of thermal energy spread as additional load on the cold room.
This feature allows a shorter defrost period (frequently around 10 minutes for each defrost), allowing the compressor an extended operation time during the day. In some cases, it is possible to use a smaller compressor on a parallel cold room with electric defrost, for the system will have more time to cool it down, making it less liable to temperature variations during defrost periods. The hot gas defrost has a small possibility to increase the moisture rate on the cold room.
Industrial refrigeration systems mostly use natural refrigerants, mainly ammonia and more recently CO2. Energy efficiency and the effective operation of those systems are the significant factors for operators of the plants. Hot gas defrost is one of the most effective ways to melt the frost formed on an evaporator. As there is an increased focus on the saving of energy consumption, performing a quick and efficient defrost is important to achieving overall energy consumption goals of the refrigeration system. In maximum cases, it would be also the most profitable way when compared to e.g. brine defrost. This article primarily focuses on valves and controls configurations that could be applied for such systems as well as the ways to optimize the process.
Gas defrost uses the system’s internal energy to defrost the evaporator, utilizing the naturally happening high temperature release vapour to add the necessary heat required to complete the defrost cycle. Through the years, refrigeration systems have working some different methods for introducing the hot gas to the evaporator. These include: reverse cycle, three pipe and reverse flow. Each of these methods has been perfected further as different manufacturers have refined the operation to suit their needs.
The profession off with hot gas defrost is the increase in difficulty and increase in electro-mechanical parts that must be trusted on. None the less some systems are key candidates for using hot gas defrosts rather than electric defrost. A heat pump system previously has all the switch over capability essential to create a hot gas defrost system. Heat pumps merely required a control system to initiate and dismiss the defrost sequence. That type of defrost is also known as a reverse cycle defrost. Ice cubes are another prime candidate for hot gas defrost. That’s because they have a massive demand for defrosts as they produce ice then immediately require heat to free up the cubes from the evaporator. Since this process repeats constantly, energy efficient defrost are required. Very large systems also are candidates for hot gas defrost systems because defrosting large evaporators takes a lot of heat and once again energy ingesting becomes an issue.