Condensing economisers are a type of heat exchanger that enables some of the sensible heat and latent heat from boiler flue gases to be recovered. This heat is normally used to preheat the boiler’s feedwater and to supply low grade heating requirements. Typically, a condensing economiser will improve boiler net thermal efficiency (expressed in percentage terms) by at least 9 percentage points (i.e. a boiler with efficiency of 84.0% is improved to at least 93.0%). The Energy Technology List (ETL) aims to encourage the purchase of higher efficiency condensing economisers.
To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.
Condensing Economisers are products specifically designed to improve boiler net thermal efficiency by recovering both sensible and latent heat from boiler flue gases.
1.3.1 Performance requirements
The product shall increase the net thermal efficiency of the boiler system to which it is designed to be fitted by at least 9.0%p., when the boiler system is operating at the test points set out in Table 1.1.
Table 1.1 Performance test points for condensing economisers
|Test point % MCR||Increase in net thermal efficiency of bioler system|
">=" means "greater than or equal to"
“%p.” means “percentage point”
Where MCR is the maximum continuous rating (MCR) of the boiler system for which the product is designed.
1.4 Measurement and Calculations
1.4.1 Measurement Standards and Test Requirements
The required minimum performance shall be demonstrated using Methods A, B or C, as set out in 126.96.36.199, 188.8.131.52 and 184.108.40.206 below:
220.127.116.11 Method A – Indirect measurement
Under this test method, product performance shall be demonstrated by measuring the improvement in net thermal efficiency of a test boiler resulting from the addition of the condensing economiser. Net thermal efficiency shall be measured at test points that are equivalent to 30%, 50% and 100% of the maximum continuous rating (MCR) of the boiler system for which the product is designed.
Boiler net thermal efficiency shall be measured in accordance with the procedures set out in BS 845-1:1987, BS EN 303-3:1999 or BS EN 304:2017.
Where BS 845-1:1987 is used, the standard test conditions are: a maximum ambient air temperature of 25 degrees Centigrade and an excess combustion air level of not less than 15%.
18.104.22.168 Method B – Direct measurement
Under this test method, product performance shall be demonstrated by calculating the improvement in boiler net thermal efficiency that will occur at 30 %, 50 % and 100 % of the maximum continuous rating (MCR) of the boiler system for which the product is designed.
This calculation shall be based on an assessment of the transfer of heat power that will occur at each of these test points.
The assessment of transfer of heat power shall be done in accordance with the procedures set out in BS EN 305:1997, BS EN 306:1997 and/or BS EN 308:1997.
22.214.171.124 Method C – validated design calculations
Under this test method:
- The product’s performance is determined from design calculations. The calculations should assess the improvement in the net thermal efficiency of a boiler system that the product will deliver at the full and part load conditions specified in Table 1.1 when tested in accordance with the procedures and test conditions specified in Method A.
- The accuracy of these design calculations shall be confirmed by interpolation and extrapolation of measurements of the improvement in net thermal efficiency actually realised by the product. The measurements shall be obtained using an indirect method (flue gas loss method) from one of the test standards specified in Method A:
a) At least one test point between 60% and 100% MCR, and:
b) At least one test point between 20% and 40% MCR.
- To be eligible, the improvement in the net thermal efficiency of the boiler system at the full and part load conditions realised by fitting the product to the boiler system shall exceed the performance thresholds specified in Table 1.1.
The test report shall include (or be accompanied by):
- a) Details of the calculations used to determine product performance.
- b) A copy of the published performance data for the product.
- c) Manufacturer’s design data for the product.
- d) The following test data, which shall be obtained with the product operating under stable conditions at each selected test point before and after fitting the product:
- I. Analysis of flue gas composition, including as a minimum, the levels of oxygen (or carbon dioxide) and carbon monoxide in the flue gas.
- II. Ambient and flue gas temperatures.
- III. Net thermal efficiency of the boiler system.
- e) Details of the boiler system used during the test.
For the avoidance of doubt the increase in net thermal efficiency of the boiler system shall be presented to one decimal place. As an example, a condensing economiser that delivers an increase in net thermal efficiency of 8.94% at 100% of the maximum continuous rating (MCR) of the boiler system for which the product is designed 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:
- In-house testing – Self-certified
- In-house testing – Self-tested and verified or cross-checked by an independent body
- Witnessed testing
- Independent testing
- Representative testing (see clause 1.5.1)
Further information regarding the first four routes can be found in Guidance Note 5 on the ETL product testing framework1.
1.5.1 Representative testing
Where applications are being made for condensing economiser products of the same constructional design to be included on the ETL, test data may be submitted for a single representative model provided that the maximum rated output of the products being applied for is not more than twice, or less than half, the maximum rated output of the product tested. Where the range of rated outputs exceeds these limits, products should be grouped into size ranges that comply with these rules, and test data submitted for one representative model for each group.
It should be noted that:
- If a manufacturer voluntarily removes a representative model from the ETL then other products linked with that representative model may or may not be permitted to remain on the ETL.
- If any product submitted under these representative model rules is later found not to meet the performance criteria when independently tested, then all products based on the same representative models will be removed from the ETL.
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.
1.7.1 Indicative review date
The next technical review is scheduled for 2023-24.
1.7.2 Illustrative future direction of the requirements
Future changes to the Specification may include:
- Absolute value of boiler system efficiency
- Requirements regarding condensate