1.1 Scope
Organic Rankine Cycle (ORC) Heat Recovery Equipment covers products that are specifically designed to convert low to high grade waste heat to electrical power by means of a closed thermodynamic power cycle that does not involve the internal combustion of fuel.
In ORC units, the captured waste heat is used to heat a working fluid. Vapour is produced, which is used to mechanically drive an electricity generator by means of an expander (e.g. turbine or screw). The low-pressure vapour is then condensed (rejecting its heat to a lower temperature heat sink) and pumped back to the higher pressure, to complete the cycle. The waste heat may be captured directly, by means of an internal or external heat exchanger, or indirectly, by means of a secondary heat recovery system. Heat rejection to the lower temperature ambient heat sink may be directly rejected to the air using a heat exchanger, or via a secondary cooling medium (e.g. cooling water).
1.2 Definitions
Organic Rankine Cycle (ORC) Heat Recovery Equipment covers products that are specifically designed to convert low to high grade waste heat waste heat to electrical power by means of a closed thermodynamic power cycle that does not involve the internal combustion of fuel.
ORC Heat Recovery Equipment is available in a range of efficiencies. The Energy Technology List (ETL) Scheme aims to encourage the purchase of higher efficiency products, which can realise substantial reductions in carbon emissions by generating more electricity from the waste heat and thereby reducing the power requirements from fossil fuel based plants.
The ETL scheme covers three categories of product:
- Remote, secondary-cooling type. These products include a complete, closed circuit for the working fluid, contained within the unit. The condensing heat-exchanger is supplied with open connections for a secondary cooling circuit (e.g. cooling water), for connection on site.
- Integral cooling type. These products include a complete, closed circuit for the working fluid, contained within the unit. The condenser rejects its heat directly or indirectly to the air, via a heat exchanger (contained within the unit). The heat exchanger may use dry air cooling, evaporative or adiabatic cooling.
- Split-circuit type. ‘Split’ type products have separate heat collection and rejection units specifically designed to be connected together during installation by pipework to create the closed circuit for the working fluid, forming a single functional unit. The main assembly includes the heat capture heat-exchanger, expander and power generator. The second unit includes the condensing heat- exchanger, for rejection of heat to the air, using dry air cooling, evaporative or adiabatic cooling.
To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.
1.3 Requirements
1.3.1 Eligibility requirements
To be eligible, products shall:
- Consist of a factory-built packaged unit or split system (comprising a main assembly and a matched heat-rejection unit, designed for connection together on site).
- Be designed to generate electricity or produce mechanical power in the ORC shaft from waste heat.
- Be rated for continuous operation with an electrical power output not exceeding 10 MWe.
- Not incorporate any form of combustion equipment, including boost burners.
- Not use water, ammonia or any water based solution as a working fluid.
- Be designed for, and include fittings for, permanent installation.
- Have an appropriate Conformity Assessment mark.
1.3.2 Performance requirements
Eligible products shall meet or exceed the minimum adjusted net efficiency set out in Table 1.1, according to the maximum temperature of waste heat that the product is designed to capture:
Table 1.1 Adjusted net efficiency thresholds for ORC Heat Recovery Equipment
|
|
Maximum design waste heat temperature (°C) |
<= 150°C |
> 150°C and <= 250°C |
> 250°C and <= 300°C |
> 350°C |
|
|
Product Category |
Minimum adjusted net efficiency, ?̅ |
|||
|
1. |
Remote, secondary-cooling type |
>= 10% |
>= 12.5% |
>= 20% |
>= 22% |
|
2. |
Integral cooling type |
>= 7% |
>= 8.9% |
>= 17% |
>= 20% |
|
3. |
Split-circuit type |
>= 7% |
>= 8.9% |
>= 17% |
>= 20% |
"<=" means "less than or equal to"
">=" means "greater than or equal to"
“>” means “greater than”
Where:
$$Net\ Efficiency,\ ƞ= \frac{Electrical\ output (kW)-Electrical\ input (kW)}{Thermal\ input (kW)}$$
And adjusted net efficiency ?̅ is defined in 1.4.1.1 below.
The electrical input applies to 100% of the electrical consumption of the product, including any pumps and fans contained within it. However, for remote, secondary-cooling type (category 1) products, the energy use of pumps and fans associated with the secondary cooling circuit should not be included as electrical input, and are not included in the net efficiency calculation.
1.4 Measurement and calculations
1.4.1 Measurement Standards and Test Requirements
The required minimum performance shall be determined using Methods A or B, as set out in 1.4.1.1. and 1.4.1.2 below.
Products can either be tested in an accredited laboratory or on-site as part of a user acceptance testing process. For the purposes of compliance and verification with the ETL requirements user acceptance testing reports shall be considered along with the manufacturers and supplier’s internal user-acceptance testing procedure. This may or may not include references to elements of BS EN 60953-2: 1996: Rules for steam turbine thermal acceptance tests. Wide range of accuracy for various types and sizes of turbines.
1.4.1.1 Method A – Direct Measurement
Under this test method, product performance shall be demonstrated by calculating the net efficiency (as defined above), from measurements of thermal input, electrical output and electrical input, in the application and at the rated capacity, for which it is designed.
The reference test conditions, which depend on the maximum temperature of waste heat (up to 350°C) that the product is designed to capture, are set out in Table 1.2 below.
Table 1.2 Reference test conditions
|
Maximum design waste heat temperature (°C) |
<= 150°C |
> 150°C and |
> 250°C and |
|
|
Reference test conditions |
||||
|
T1 – inlet temperature of the captured waste heat source |
150°C |
250°C |
350°C |
|
|
T2 – inlet temperature of the heat rejection sink |
Remote, secondary cooling type products |
30°C |
30°C |
30°C |
|
Integral cooling type products |
20°C |
20°C |
20°C |
|
|
Split-circuit type products |
20°C |
20°C |
20°C |
|
At the reference conditions, the adjusted net efficiency, ?̅, is equal to the net efficiency ?, as defined above.
For temperature of waste heat greater than 350°C, the adjusted net efficiency, ?̅, shall be calculated on the actual temperatures T1 and T2, and is equal to the net efficiency ?, as defined above
Where the application does not make it feasible for tests to be carried out at the conditions above, then alternative inlet temperatures T1 and T2 can be used. In such cases, the adjusted net efficiency, ?̅, should be calculated as defined in Table 1.3 below.
Table 1.3 Adjusted net efficiency for alternative inlet temperatures (for temperature of the waste heat less than 350°C)
|
Maximum design waste heat temperature (°C) |
<= 150°C |
> 150°C and <= 250°C |
> 250°C and <= 350°C |
|
T1 (allowable range) |
<= 150°C |
> 150°C and <= 250°C |
> 250°C and <= 350°C |
|
Remote, secondary-cooling type products Adjusted net efficiency, ?̅= |
$$ƞ(\frac{150-30}{T1- T2})(\frac{273.15+T1}{273.15+150})$$ |
$$ƞ(\frac{250-30}{T1- T2})(\frac{273.15+T1}{273.15+250})$$ |
$$ƞ(\frac{350-30}{T1- T2})(\frac{273.15+T1}{273.15+350})$$ |
|
Integral cooling and split circuit type products Adjusted net efficiency, ?̅= |
$$ƞ(\frac{150-20}{T1- T2})(\frac{273.15+T1}{273.15+150})$$ |
$$ƞ(\frac{250-20}{T1- T2})(\frac{273.15+T1}{273.15+250})$$ |
$$ƞ(\frac{350-20}{T1- T2})(\frac{273.15+T1}{273.15+350})$$ |
Note: T1 and T2 above are defined in Table 1.2 and expressed in degrees Celsius.
The adjusted efficiency, ?̅, shall meet or exceed the associated minimum adjusted net efficiency threshold defined in Table 1.1.
For example, a category 1 ORC product designed for a maximum waste heat temperature of 200°C, with a net efficiency of 10.8% (T1 = 200°C and T2 =30°C), will have an adjusted net efficiency of 12.6%, and therefore deemed eligible.
The assessment of thermal input, electrical input and electrical output shall be made by the manufacturer testing using harmonised standards or other reliable, accurate and reproducible state-of-the-art methods. This may or may not include references to elements of BS EN 60953-2: 1996: Rules for steam turbine thermal acceptance tests. Wide range of accuracy for various types and sizes of turbines.
1.4.1.2 Method B - Validated Design Calculations
Under this test method, product performance shall be demonstrated by calculating net efficiency (as defined above), from design calculations.
The accuracy of these calculations shall be confirmed by interpolation and extrapolation of measurements obtained from tests (carried out according to Method A above) of at least two units of the same basic design as the product, i.e.:
- Use the same working fluid as the product
- Use the same thermodynamic cycle
- Have the same expander type – i.e. manufacturer, method of expansion (e.g. reciprocating, turbine, or screw)
- Use the same heat exchanger types – for both waste heat capture and heat rejection to the ambient heat sink;
- Use the same method of rejecting heat to the ambient heat sink – i.e. water-cooled; or dry or evaporative air-cooled.
The product shall have a rated maximum electrical output of no more than 20% greater or smaller than one of the tested products.
The test report shall include (or be accompanied by):
- Details of the methodology and calculations used to determine product performance
- A copy of the published performance data for the product
- Manufacturer’s design data for the product
- The following data for the tests carried out according to Method A and for the design conditions of the product:
I. Details of the composition, specific heat capacity, inlet and outlet temperatures, and flow-rates of:
- The captured waste heat source
- The low-temperature heat sink
II. Electricity output and input
III. Calculated net efficiency and adjusted net efficiency
- Details of main components of the tested units and (where these are not identical to the product) calculations demonstrating that their performance can be used to validate that of the product, including:
I. Heat exchangers
II. Expander
III. Alternator
1.4.2 Rounding
For the avoidance of doubt, test data should be presented to one decimal place. As an example, a remote, secondary-cooling type product designed to capture waste heat with a temperature of 125°C, with an adjusted net efficiency of 6.9%, would be deemed to be a fail.
1.5 Verification for ETL Listing
Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:
- Witnessed testing
- Independent testing
- User Acceptance tests or Field Trials (see Method A – 1.4.1.1)
- Representative testing (see Method B – 1.4.1.2)
Further information regarding the first three routes can be found in the ETL Testing Framework.
1.6 Conformity testing
Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.
1.7 Review
1.7.1 Indicative review date
This specification is scheduled to be reviewed during the 2024/25 review cycle.
1.7.2 Illustrative future direction of the requirements
The next technical review will consider:
- Increasing performance thresholds
- Introduction of newer refrigerant and their GWP requirements