Copper vs Test Results Show Impact on Performance and Costs
Table of Contents Introduction... 2 Test Information... 2 Cylinder Information... 3 Theory... 4 Heat-Up Test... 5 Apparatus... 5 Procedure... 6 Initial Heat-Up Procedure... 6 Continuous Heat-Up Procedure... 6 Test Results... 7 Discussion... 12 Costing Comparison... 13 Conclusion... 14 References... 14 Figures Figure 1: Cylinder Design... 3 Figure 2: Conversion Equation (m 3 kwh)... 4 Figure 3: Conversion Equation (ft 3 kwh)... 4 Figure 4: Heat-Up Test Apparatus... 5 Figure 5: Initial Heat-Up Tests - Hot Water Draw Temperature... 8 Figure 6: Continuous Heat-Up Tests - Hot Water Draw Temperature... 9 Figure 7: Initial Heat-Up Tests - Water (Thermostat Pocket) Temperature... 10 Figure 8: Continuous Heat-Up Tests - Water (Thermostat Pocket) Temperature... 11 Tables Table 1: Heat Exchanger Materials & Thermal Conductivity... 2 Table 2: Cylinder Details... 3 Table 3: Calorific Values of Gas Supplied... 4 Table 4: Heat-Up Tests Temperature Results... 7 Table 5: Heat-Up Tests Gas Consumption Results... 7 Table 6: Cylinder Comparison - Heat-Up Time and Gas Consumption... 12 Table 7: Average Fuel Cost per Cylinder... 13 Table 8: Total Average Money saved between Cylinders... 13 Table 9: Money Saved per Year, compared to... 14 Page 1
Introduction Copper and are the 2 most common materials used for hot water cylinders and their heat exchangers, due to their similar properties such as resistance to corrosion. Arguably, between the 2 materials, Copper is seen as the more beneficial to use, mainly due to its high thermal conductivity as well as other properties 1, such as its Antimicrobial properties 2. Below are some other examples of materials used in Heat Exchangers and their thermal conductivities; Material Thermal Conductivity 3 (Btu/(hr-ft-F)) (W/m.K) Copper 233 386 Aluminium 118 204 Titanium 13 232 26 45 Table 1: Heat Exchanger Materials & Thermal Conductivity Due to recent increases in the price of the material, copper cylinders have become more expensive to manufacture and more customers start to look towards cheaper options. Some opt for a Stainless Steel cylinder, due to the lower initial price. However, whilst both cylinder types are highly efficient for providing customer hot water needs, this report proves Copper cylinders to be faster, more efficient and more cost effective than Stainless Steel cylinders. Ultimately meaning that a Copper cylinder is better value in the long term. Test Information The following report details the Heat-Up tests set up to compare 3 similar cylinders; a (Copper) Cylinder from our range of Unvented Cylinders, an Cylinder, and a premium Cylinder. Each test is carried on each cylinder individually. The Heat-Up tests objective is to time how long a cylinder takes to heat up the stored water from cold (8-12⁰C) to an approximate temperature of 60⁰C, and how much gas is consumed. There are 2 types: Initial Heat-Up and Continuous Heat-Up. The Initial Heat-Up test starts with the boiler initially switched off, so both the cylinder coil and stored water are cold. This is to reflect an initial heat-up of a newly installed Hot Water Storage cylinder. The Continuous Heat-Up test will start with the boiler already switched on, but the water stored in the cylinder is cooled to its lowest temperature. This is to reflect the standard heatup of an already installed Hot Water Storage cylinder. 1 http://www.mcdonald-engineers.com/copper-facts 2 http://www.microgroove.net/press/copper-helps-shanghai-bus-users-breathe-easy 3 http://www.engineersedge.com/properties_of_metals.htm Page 2
Cylinder Information For the following tests, 3 similar cylinders were selected to compare. The 4 (Copper) and cylinders are indirect unvented heating cylinders with a storage capacity of 210 Litres. The cylinder is the same cylinder used in testing, but the coil has been replaced with a 3m sq. finned copper coil to improve the cylinders heating efficiency. These additional features are available for all other cylinders. Further details of each cylinder can be viewed in Table 2 below. Figure 1: Cylinder Design A B C D E E1 E2 Cylinder Body Incoming Mains Thermostat Pocket Hot Water Draw Coil Coil Heating Flow Coil Heating Return 5 Cylinder Code C77 -- -- Overall Height 1550 mm 1550 mm 1500 mm Overall Diameter 550 mm 550 mm 550 mm Insulation Thickness 50 mm 50 mm 50 mm Storage Capacity 210 Litres 210 Litres 210 Litres Cylinder Type Indirect Indirect Indirect Vented/Unvented Unvented Unvented Unvented Table 2: Cylinder Details 4 http://www.mcdonald-engineers.com/products/unvented-hot-water-cylinder 5 http://www.mcdonald-engineers.com/products/powerflow/specifications-sizing Page 3
Theory For this comparison between Hot Water Cylinders, it is crucial to monitor the gas consumption of all cylinder types. The boiler used for testing has a metric meter installed to give the gas readings, which are to be recorded at the start and end of each test. The amount of gas consumed will be the difference between both readings. With a Metric meter all gas readings are in cubic meters (m 3 ), whereas with an Imperial meter all gas readings are in cubic feet (ft 3 ). To estimate the average gas bill for each cylinder, the gas readings must be converted into kilowatthours (kwh) using the formulas below. For Metric Meters: Gas Consumed (kwh) = Gas Volume (m3 ) Calorific Value (MJ m 3 ) 1.02264 3.6 For Imperial Meters: Legend 6 Figure 2: Conversion Equation (m 3 kwh) Gas Consumed (kwh) = Gas Volume (ft3 ) 2.83 Calorific Value (MJ m 3 ) 1.02264 3.6 Conversion Factor (ft 3 m 3 ) = 2.83 Conversion Factor (m 3 kwh) = 3.6 Correction Factor = 1.02264 Calorific Value 7 = See Table Below 8 Figure 3: Conversion Equation (ft 3 kwh) Charging Zone Calorific Value (MJ/m 3 ) East Midlands 39.7 Eastern England 39.2 Northern England 39.9 Scotland 39.5 Southern England 39.5 Wales North 40.2 Wales South 39.4 West Midlands 39.7 Table 3: Calorific Values of Gas Supplied 6 http://www.britishgas.co.uk/business/help-and-advice/glossary.html 7 For all calculations in this report, Calorific Value = 39.5 MJ/m 3 (Scotland) 8 Calorific Value Report (17/02/2017) found at: http://www2.nationalgrid.com/uk/industry-information/gastransmission-operational-data/report-explorer/ Page 4
Heat-Up Test Apparatus Important Notes All [X] labels refer to Figure 4. All cylinders are installed and tested by on-site plumbers before apparatus can be set-up. The Data Logger [B], connected to the laptop [A], consists of 6 probes to measure following temperatures every 15 seconds: Incoming Mains / Cold Feed [B1] Room Temperature [B2] Thermostat Pocket [B3] Hot Water Draw Off [B4] Primary Coil Flow [B5] Primary Coil Return [B6]. The room temperature probe [B2] is attached to a pole and placed away from the cylinder, whilst the Thermostat probe is placed within the thermostat pocket [B3] of the cylinder, along with the Thermostat. Additional T-section piping was installed at the Incoming Mains [B1], Hot Water Draw [B4], and Primary Coil Connections [B5, B6] for the remaining probes to sit in. This will give more accurate temperature readings. Figure 4: Heat-Up Test Apparatus A B B1 B2 B3 B4 B5 B6 C Laptop Data Logger Temperature Probe: Incoming Mains Temperature Probe: Room Temperature Temperature Probe: Thermostat Pocket Temperature Probe: Hot Water Draw Off Temperature Probe: Coil IN Temperature Probe: Coil OUT Hot Water Cylinder Page 5
Procedure Important Notes Testing procedure and component labels refer to Figure 4. Each cylinder is tested individually with the following procedures. Initial Heat-Up Procedure 1. All valve connections to cylinder must be checked to be open. 2. Set Thermostat dial to 60⁰C. 3. Record the gas reading on boiler. 4. Switch on boiler and start the data logger [B]. 5. Leave Cylinder to heat up, until Thermostat cuts off at 60⁰C. 6. Switch off the boiler and stop the recording. 7. Record gas reading on boiler. 8. Save all recorded data. 9. Run hot water until cold (approx. 20 minutes). 10. Once water temperature (Stat Pocket Temperature) has been cooled to the lowest possible temperature, repeat steps 4 9 for following tests. 11. Once all test have been completed, close cold feed valves and drain cylinder. Continuous Heat-Up Procedure 1. All valve connections to cylinder must be checked to be open. 2. Set Thermostat dial to 60⁰C and switch on the boiler. 3. Run hot water tap to keep Hot Water Draw [B4] and the Stat Pocket [B3] temperatures cool. 4. Whilst tap is running, monitor cylinder until Coil Heating flow in [B5] temperature has reached approximately 60 70⁰C. 5. Once temperatures have stabilised, close hot water tap and start the data logger [B]. Record gas reading on boiler. 6. Leave cylinder to heat up, until Thermostat cuts off at 60⁰C. 7. Stop the recording, and record both gas reading on boiler. 8. Save all recorded data. 9. Run hot water until cold (approx. 20 minutes). 10. Repeat steps 4 9 for following tests. 11. Once all tests have been completed, close cold feed valves and drain cylinder. Page 6
Test Results Cylinder Test Number Heat Up Time Thermostat Pocket (B3) Hot Water Draw Off (B4) Test Start Test End Test Start Test End (minutes) (⁰C) (⁰C) (⁰C) (⁰C) Initial 1 48.25 10.01 60 9.99 58.9 Initial 2 45.75 12.03 60.02 11.97 60.06 Cont. 1 42.5 12.25 60.15 12.63 60.36 Cont. 2 42.5 12.44 60.14 12.14 60.05 Initial 1 40 9.22 59.39 16.11 60.4 Initial 2 41.75 9.22 60.02 10.49 59.19 Cont. 1 37.25 12.16 60.07 18.01 58.95 Cont. 2 37.5 12.31 60.02 16.63 58.59 Initial 1 53.75 8.94 59.75 9.25 49.99 Initial 2 54.5 8.2 60.11 12.84 50.5 Cont. 1 51.25 12.72 60.11 10.66 51.78 Cont. 2 51.25 12.2 60.45 10.3 51.9 Table 4: Heat-Up Tests Temperature Results Cylinder Gas Reading (Metric) Test Heat Up Time Gas Consumed Number Test Start Test End (minutes) (m 3 ) (m 3 ) (m 3 ) (kwh) Initial 1 48.25 93.353 94.674 1.321 14.822 Initial 2 45.75 163.667 164.98 1.313 14.733 Cont. 1 42.5 161.174 162.378 1.204 13.51 Cont. 2 42.5 165.045 166.244 1.199 13.453 Initial 1 40 82.19 83.504 1.314 14.744 Initial 2 41.75 129.383 130.688 1.305 14.643 Cont. 1 37.25 125.456 126.603 1.147 12.87 Cont. 2 37.5 126.844 127.997 1.153 12.937 Initial 1 53.75 130.853 132.334 1.481 16.618 Initial 2 54.5 133.809 135.311 1.502 16.853 Cont. 1 51.25 138.374 139.709 1.335 14.979 Cont. 2 51.25 141.297 142.633 1.336 14.991 Table 5: Heat-Up Tests Gas Consumption Results Page 7
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 70 Hot Water Draw Temp. ( C) - Initial Heat-Up Tests 60 50 40 30 20 10 0 TIME (MINUTES) Initial Test 1 Initial Test 2 Initial Test 1 Initial Test 2 Initial Test 1 Initial Test 2 Figure 5: Initial Heat-Up Tests - Hot Water Draw Temperature Page 8
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Hot Water Draw Temp. ( C) - Continuous Heat-Up Tests 70 60 50 40 30 20 10 0 TIME (MINUTES) Cont. Test 1 Cont. Test 2 Cont. Test 1 Cont. Test 2 Cont. Test 1 Cont. Test 2 Figure 6: Continuous Heat-Up Tests - Hot Water Draw Temperature Page 9
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 70.00 Water (Stat Pocket) Temp. ( C) - Initial Heat-Up Tests 60.00 50.00 40.00 30.00 20.00 10.00 0.00 TIME (MINUTES) Initial Test 1 Initial Test 2 Initial Test 1 Initial Test 2 Initial Test 1 Initial Test 2 Figure 7: Initial Heat-Up Tests - Water (Thermostat Pocket) Temperature Page 10
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Water (Stat Pocket) Temp. ( C) - Continuous Heat-Up Tests 70 60 50 40 30 20 10 0 TIME (MINUTES) Cont. Test 1 Cont. Test 2 Cont. Test 1 Cont. Test 2 Cont. Test 1 Cont. Test 2 Figure 8: Continuous Heat-Up Tests - Water (Thermostat Pocket) Temperature Page 11
Discussion Besides the Continuous Heat-Up tests proving to have a faster heat-up time than the Initial Heat-Up tests, the results show that from the fastest to slowest cylinders; the had heated up the fastest and consumed the least amount of gas, then the standard, and the slowest was the which had consumed the most gas during heat-up. This is shown in the table below. Cylinder Difference Heat-Up Test Heat-Up Time Average Gas Consumption (Minutes) (m 3 ) (kwh) vs. Stainless Initial 7.13 0.175 1.958 Steel Continuous 8.75 0.134 1.504 vs. Stainless Initial 13.25 0.182 2.042 Steel Continuous 13.88 0.186 2.081 vs. Initial 6.13 0.008 0.084 Continuous 5.13 0.051 0.578 Table 6: Cylinder Comparison - Heat-Up Time and Gas Consumption Comparing the Test End temperatures from Table 4, the Hot Water Draw (B4) temperature was lagging behind the Thermostat (B3) temperature for the cylinder. This had occurred throughout every Heat-Up test, meaning the water temperature was cooler at the top of the cylinder compared to the centre by approximately 10⁰C. It was not until the hot water tap was running for 1 minute that the 60⁰C water had risen to the cylinder top and the hot water draw off pipe. This could be due to the s coil, which was located at the bottom of the cylinder. Comparatively both the and coils cover a larger area inside the cylinder, giving more equal heat distribution to the water volume. This is why both the Thermostat (B3) temperature and Hot Water Draw (B4) temperature (top of cylinder) were approximately the same temperature for the and cylinder, and shows that both these cylinders stored more heat than the. Additionally, from Figure 7 and Figure 8, the Thermostat temperature rise for the fluctuates noticeably in comparison to the and. This could be due to the s Thermostat pocket being a bigger size than the Thermostat used in testing. Comparatively the pocket on the is smaller, giving more accurate readings of the water temperature for the Thermostat (B3). Page 12
Costing Comparison Taking into account the average gas consumed, and assuming an average number of 2 Heat-ups per day (1 Initial heat-up and 1 Continuous heat-up) for 1 year (365 days), the following tables show an estimate of the average fuel cost for each cylinder and money saved between cylinder usage, based on the average fuel prices of Scotland/England/Wales (4.18 pence/kwh) and Northern Ireland (4.08 pence/kwh) 9. Note: The following costs do not include standard tariff or VAT. Cylinder Type Scotland, England, Wales Northern Ireland Heat-Up Average Gas Consumption Heat-Up Cost Total Cost Heat-Up Cost Total Cost (m 3 ) (kwh) (Per day) (Per year) (Per day) (Per year) Initial 1.317 14.778 0.62 0.60 431.15 Continuous 1.202 13.482 0.56 0.55 420.84 Initial 1.309 14.693 0.61 0.60 421.05 Continuous 1.150 12.904 0.54 0.53 410.97 Initial 1.492 16.736 0.70 0.68 483.96 Continuous 1.336 14.985 0.63 0.61 472.39 Table 7: Average Fuel Cost per Cylinder Cylinder Difference Scotland, England, Wales Saved Total saved (Per day) (Per year) Northern Ireland Saved (Per day) Total saved (Per year) vs. 0.14 52.81 0.14 51.55 vs. 0.17 62.91 0.17 61.41 vs. 0.03 10.10 0.03 9.86 Table 8: Total Average Money saved between Cylinders 9 http://www.energysavingtrust.org.uk/about-us/our-calculations Page 13
Conclusion From what the Heat-Up tests have shown, both of the Copper cylinders ( and ) have proven to heat up faster, store more heat and consume less gas than the premium Stainless Steel cylinder. Between the 2 Copper cylinders, the proved to be the fastest and most efficient hot water cylinder, heating up the quickest and consuming the least amount of gas for each test. In terms of cost, more money would be saved per year using either of the 2 Copper cylinders compared to the cylinder, as shown in the table below. Money Saved per Year Cylinder Scotland, England, Wales Northern Ireland Standard Copper 52.81 51.55 62.91 61.41 Table 9: Money Saved per Year, compared to So whilst the initial cheaper cost of a stainless steel cylinder seems better at supplying all heating needs, it is more beneficial in the long run to invest in a copper cylinder to provide efficient heating for the household and save more money on the gas bill for the end of the year. References http://www.mcdonald-engineers.com/copper-facts http://www.microgroove.net/press/copper-helps-shanghai-bus-users-breathe-easy http://www.engineersedge.com/properties_of_metals.htm http://www.mcdonald-engineers.com/products/unvented-hot-water-cylinder http://www.mcdonald-engineers.com/products/powerflow/specifications-sizing http://www.britishgas.co.uk/business/help-and-advice/glossary.html http://www2.nationalgrid.com/uk/industry-information/gas-transmission-operationaldata/report-explorer/ https://www.ukpower.co.uk/home_energy/gas_meter_readings http://www.energysavingtrust.org.uk/about-us/our-calculations Page 14