How It Works
Our Organic Rankine Cycle Solutions
ElectraTherm has two organic Rankine cycle solutions available to the public. The first is the Power+ Generator, our heat to power generating system designed for upcycling waste heat – such as the jacket water and exhaust gases from engines – into clean electricity.
The second (and what the team at HQ is most excited about) is the Active Cooler, the world’s only net-zero power cooling solution that not only saves energy but creates it. If you are expelling large amounts of heat – then this state of the art cooler could be the ultimate radiator replacement.
Although these two products seemingly perform very different tasks, they are in fact one in the same. This is because the basis of design for the Active Cooler is the Power+ Generator.
- Working fluid is pumped to a higher pressure and transferred to the preheater.
- The temperature of the working fluid is increased in the preheater and sent to the evaporator.
- Heat captured by the evaporator boils the working fluid into a high pressurized vapor.
- Vapor flows through the twin screw expander, spinning an electric generator to produce power.
- The vapor is cooled and condensed back into a liquid and the cycle repeats.
TWIN SCREW EXPANDER
The POWER+ uses a twin screw expander as its power block; which effectively is a compressor operating in reverse. The twin screw expander design is robust and simple. The operating speed is relatively low (<5000 RPM) and does not require a gearbox to drive the generator.
A significant advantage of the twin screw expander is the ability to operate in two phase, or “wet” conditions. This two phase operation means that the refrigerant does not have to be 100% vapor. The ability to operate in a range of working fluid conditions from superheat to wet vapor allows the POWER+ to follow variable heat loads and produce power over a wide range of input conditions. This is particularly important when load following internal combustion engines through different speed and load conditions.
An induction generator is electro-mechanically similar to an induction motor. In the case of our systems, the induction generator is based on a 70-100 horsepower (about 50-75 kW) squirrel cage motor with some optimizations to the internal construction to make it more efficient as a generator. In the event of a loss of grid, the unit will automatically shut down, and cannot be re-started until line conditions return to normal.
BRAZED PLATE HEAT EXCHANGERS
The superior brazed construction of the heat exchangers used in our offerings have no gaskets or loose parts, improving their reliability while minimizing maintenance costs. Brazed plate heat exchangers are considered one of the most efficient ways to transfer heat – they provide unmatched performance with lower life-cycle costs – amounting to savings in space, energy, and maintenance.
The working fluid that is used is the compound HFC-245fa (1,1,1,3,3 pentafluoropropane). HFC-245fa is an EPA-approved member of the hydro fluorocarbon (HFC) family of refrigerants, permitted under the Montreal Protocol. This non-flammable, low-toxicity, environmentally-safe fluid boils at approximately 15.5°C at atmospheric pressure. HFC-245fa is ozone safe and generally safe to handle. The oil used for lubrication is contained in the working fluid as part of ElectraTherm’s proprietary in-process lubrication.
The Power+ Generator offers two condensing options—air-cooled and water-cooled. The use of an air cooled condenser condenses the working fluid outside the Power+ Generator . On the other hand, when a water cooled condenser is used, the working fluid is condensed in the water cooled condenser which is located inside the Power+ Generator. Water cooled condensers can be utilized as cooling towers and closed liquid loop radiators.
Site conditions, such as the system delta T (which is affected by ambient air temperature and temperature of heating/ cooling water) and available thermal heat all affect ORC performance.
SYSTEM DELTA T
System delta T is the ΔT temperature differential between the hot source and condensing source, and is also the primary driving force behind increased efficiency in ORC systems. The temperature ranges for TH and TC that low grade heat ORC systems typically operate in will dictate lower efficiencies than high grade heat ORC systems because of the higher heat source temperature TH. The Power+ system is limited by delta T temperature because of the physical properties of liquid water.
The Power+ Generator’s location influences the ambient air temperature conditions. In locations with hot climates, such as Africa and the Equator, Power+ net power output will be lower than net power outputs produced by machines that are installed in cold climate locations, such as Northern Europe, even at the same hot water input temperature. This discrepancy is due to a lower system delta T (difference between the hot water input and condensing temperature) in hot climates versus that in cold climates.
AVAILABLE HEAT / THERMAL POWER
Available thermal power is the rate of BTUs/hr or kWth that is continuously produced by the waste heat source and available to be consumed by the Power+ Generator. Available thermal power affects the performance of the Power+ because the Power+ Generator converts thermal power into electricity. Simply put, less thermal power equates to less electrical output.
HEAT ENGINE EXAMPLE
A heat engine is a simple engine that converts thermal heat into mechanical work. A heat engine operates by extracting heat from a hot reservoir and moving it over to a cold reservoir, generating work in the process.
In order to maximize the amount of work a heat engine can produce, the temperature of the hot reservoir needs to be increased as much as possible, whereas the temperature of the cold reservoir needs to be reduced.
An ideal (theoretical) heat engine operates at the Carnot efficiency. The Carnot efficiency is the maximum possible efficiency that any engine can achieve, regardless of size, complexity, money spent or the amount of time allowed for the engine to perform work. Carnot efficiency can be calculated by the expression:
W is energy exiting the system as work, or in our case, electricity.
QH is heat put into the system.
TC is the absolute temperature of the cold reservoir (the cooling source temperature).
TH is the absolute temperature of the hot reservoir (the hot water supply temperature).
When calculating the Carnot efficiency, all temperatures are given with respect to absolute zero, i.e. for Celsius temperatures you must add 273.15 to convert to Kelvin scale.
Carnot efficiency is a theoretical efficiency that cannot be accomplished in reality. In reality, the efficiency of any heat engine is significantly reduced by various factors such as heat loss, pressure drops, and frictional losses.