1 ................................................................................................................................21 Acknowledgements Manilka Abeysuriya for expert advice on flow calculations William Dowell for help in our planning stages and various figures aiding our calculations Christopher Edwards for sourcing components and tutoring us in creating our PIC Hannah Williams for mentoring us from the start...........................20 Appendices.....................................................................................3 Weekly plans.....................................................6 Analysis of current products...........................................................................................................................................................................................................................................................7 Plan.................4 Our School and Team..............................................................................................................................................................................................................................19 Bibliography............................................................................................................................Contents Acknowledgements............9 Creating our testing rig.............................................................6 Showers...................................................................................................................5 Research.........................................................................................................................................................................................................................................................................................................................................................................................................................6 Domestic Plumbing......................................................................................................................3 Introduction........................................11 Display Model.................................................................17 Conclusions.......................................................................18 Recommendations....................................................2 Time Management........................................................................................................................................1 Summary..........................9 Results..........................................................................4 Brief.......................................................4 Situation....4 Our Company – Pera..............................................................8 Implementation......................................................... providing advice (and common sense!) throughout and critiquing this report 2 ................................................................................................................................................................................................................................................................................................................................................................ Summary 3 . Gantt Chart See Appendix B 4 .Time Management Weekly plans Mark Pollock creates a weekly plan detailing the exact objectives of each member of the team for each session we have. See Appendix A for an example. from manufacturing through to the consumer. Product Development. GUI design. Will Alexander and Max Jones. fluids) and microwave work (heating/drying. It is located in Oakham. Once a product is designed. Pera Technologies has many groups of staff to tackle their extremely varied work. this heat is experienced briefly and some is imparted on the air and the user. (Around 4.18J is needed to heat 1 gram (and thus 1cm) of water by 1C. offering.) In showers. Government Services and Workplace Training. heat is transferred by conduction to the colder fluid. respectively. When a hot fluid flows in one pipe and a cold fluid flows in the other. Pera Consulting and Pera Training. Pera Technologies can also construct supply chains of partners to get the product onto the market. The team is made up of four students. It was Pera Technologies that provided us with our task and their support. works in their Informatics and PMM groups and so covers With informatics: control systems. A heat exchanger runs two pipes made of a good thermal conductor alongside each other. but the majority remains in the waste water and is lost down the drain. details of which are found in the bibliography. communications. thermal. Rutland. desktop/web applications. Our link engineer. radar) Our School and Team Oakham School is a coeducational boarding and day school for ages 10-18 that offers both the International Baccalaureate and A-Levels in its Upper School. Manilka Abeysuriya. they work on a huge range of products and have specialised engineers covering many areas of physics and mechanics. Furthermore. meaning a lot of energy is required to raise its temperature. databases With PPM: Modelling (structural. of all sizes. 15 – 20% of domestic energy is used for heating water for ablution processes. Situation Note: Bracketed numbers indicate the source used. They are a leading product development contractor and work with companies across Europe. This is due to the large volumes heated and because water has a high specific heat capacity. A heat exchanger can be used to recycle some of this heat. To increase the efficiency of a 5 . Mark Pollock. these being Pera Technologies. material processing. tested and approved. Our supporting teacher is physicist Miss Hannah Williams.Introduction Our Company – Pera Pera is a company with three main branches. all currently studying AS level physics: Harry Smith. the hot waste water is run in one pipe while cold. This reduces the amount of hot. The end product is desirable as it provides a way to reduce the large cost of showering. namely. They wanted us to take up the project and .find potential improvements to their initial concept. shooting to ₤918 if a power shower is used. mains water is run through the other.shower (from 0% . as fossil fuels are burnt to either directly heat water or to create the electricity used to heat water. To do this. 5.as hopefully we would look at it from a different point of view . thereby reducing the energy used.3% of the UK’s energy is used to heat water and any reduction in this could have huge positive environmental impacts. becoming slightly heated. This warmer water is directed to the shower and mixed with the hot input. 6 . to be fitted when new showers are installed 2) The cost of the system plus the cost of retrofitting it to existing showers Ideally. Two separate costs need to be considered: 1) The cost of the system on its own. the typical UK home spends ₤416 per year on showers. We must find out if the energy recouped is too small to warrant the cost of a heat recovery system. (1) Brief We have been tasked with testing the viability of the method of re-using the hot water from showers using heat exchangers. we want a system where this second set of costs is outweighed by the savings of the system. boiler water required per shower. reduction in CO2 emissions. Pera had already been experimenting with this idea using different configurations to determine whether this is a viable option for domestic use.usually no heat is recycled). we must design a heat recovery system (that should be retrofit-able) and then create a method of testing its energy savings. On a larger scale. ) Also on the market are various 7 . the statistics provided by the Standard Assessment Procedure quoted on the Shower Save website (and included above) are questioned by Which? who give far lower figures for the systems’ efficiencies.Research How a heat exchanger works We started out. presumably like the majority of the public. unaware of what exactly a heat exchanger is or how it works. for a reasonably small increase in efficiency. FIGURES??? Doubt as to their claimed sales figures is furthered on this site: http://www. RT-1 by Shower Save: A large. This is improbable. system A involves removing a mains water feed from one of the shower or boiler and directing one feed into both appliances. for cost reasons.03 for a BETTE shower tray if your own does not accommodate the Recoh Tray. having been warmed by the heat exchanger travels to both the shower and the boiler with a claimed 47% efficiency. Cost: £680. circular heat exchanger system. Analysis of current products Recoh-Tray.89 . This is much more labour intensive than either B or C and will raise the installation price.£294. However. See Appendix C for flow diagrams of their three systems. given the nature of heat exchangers: they divide heat between two water feeds.uk/microsite/shower-heat-exchange-and-recovery-system Who claim that using a string of another of Shower Save’s products.00 (not including labour) (plus £216. use systems B or C. the Recoh Vert RV-3 they have created a 45-50% efficient system. increasing the pay back time. while Shower Save claim a rating of 66% efficiency for one of these.co. B) Warmed water travels just to the shower with a claimed 39% C) Warmed water travels just to boiler with a claimed 41% efficiency. so the output feeds should each have 50% of the heat at best. Furthermore. on top of inserting the heat exchanger into the system. They propose three systems for their heat exchanger: A) Mains water. This reduces the appeal of the product as its peak ability may not be seen by many users who.wholebuild. (2) However. A diagram of a Yorkshire joint versus a Compression fitting is below: (PICTURES TO BE TAKEN) 8 . Quite possibly. A typical shower (8 minutes long) using a regular shower uses 62 litres (1). we were quite lucky that local supply dictated that only 'Yorkshire joint' style.Showers Types: As mentioned in the situation section. while a power shower uses 136 litres (this second figure is almost twice as much a bath) (1). However. Total usage depends on the number of people using the shower and the number of showers they have per day. Use: Daily usage – The average shower length is 8 minutes. Waste pipe diameter – 40mm diameter pipe (Various plug diameters. (5) Fittings: As there is a plethora of different types of domestic plumbing fittings. We will test a range of temperatures and record the efficiency of the system at each. Greatest savings will come with the greatest use of a shower. Our final solution may need to be adapted for use in such circumstances. then we were restricted to compression fit fittings.60C (2) Parameters: Shower tray depth – 100/90/6 cm (2) Therefore we have very limited space with which to work with. a custom built heat exchanger may need to be developed. for an eventual product. the 1 bar minimum is not assured for apartment blocks as the height water is required to be raised diminishes the pressure. Average mains cold temperature – 15C (varying through the year around this point) (2) (and our own measurements using temperature sensors and a data logger are another source) Average boiler water temperature . (1) Average shower temperatures – Between 35 and 40C (based on internet research (4) and the team’s own recordings). or Conex Compression fit were available. As the laboratory that we were in for the majority of the plumbing did not have blowtorch facilities. but almost all lead to a 40mm waste pipe) (2) Domestic Plumbing Pressure: 1 bar gauge pressure is certified by the nation’s water companies. pressures in excess of 4 bar are usual. 40. regular and power showers use very different amounts of water. 50 or 90. has a temperature of 15°C. less energy is wasted and the shower is more efficient.2. we feel this is an over-simplification of the diagram. temperature of the cold input will equal roughly half that of the hot input. See Figure 1. the lack of a cold input causes the shower pump to work too hard to draw in water that isn’t there.3 mixed in to provide normal shower temperature. the hotter the cold input gets as a increasingly hot shower output. This means less heat is wasted.1 Firstly. on average. there is flaw to this layout. However. we have found a number of problems with the original ideas. the longer the shower runs. The mixing valve was already included in the shower assembly so we were tasked with finding a suitable pump and heat exchanger combination to make this system an improvement over a normal shower.3. and while probably created assuming that “mains water supply” covers both hot and cold. and a cold input that travels through the heat exchanger. due to increased cold input temperature. However. the ‘cold’ Figure 1.1. Our engineer decided a pump was necessary to ensure the flow rate and pressure are great enough to reach the mixing valve and be powerful enough shower. Using a simple siphoning process. us for a company’s Figure 1. Also. it appears to lack a mains hot water input.Plan The initial flow diagram for the system Pera have provided is seen in Figure 1. Due to all cold water passing exchanger. Our other problem with the Pera diagram is the presence of an additional pump after the heat exchanger. gaining heat in the process that joins the hot input pipe before the mixing valve. (Mains cold water. at first we hadn’t thought about this. It wasn’t until we tested the flow rate of water through our heat exchanger that we realised a pump wasn’t necessary. potentially damaging some models of shower. the cold water un- Our solution is similar to Harry’s. See Figure 1. Therefore result less one major through the heat result of Eventually. Mains water 9 . and a cold input that travels through the heat exchanger. a hot input straight from mains to the mixing valve. This also worked (despite the manufacturer’s instructions) regardless of what orientation the heat exchanger was in. the shower would only ever use cold water.2 is already warmed slightly and as a hot water has to be used. Therefore the ‘cold’ is already warmed slightly and as a result less hot water has to be Figure meaning 1. In fact. scalding hot shower up to 60 degrees Celsius. If Figure 1 was followed blindly. creating one very cold and undesirable shower!) Our initial solution was to have a hot input straight from mains to the mixing valve. we have established that flow through the heat exchanger is almost unrestricted. gaining heat in the process. meaning no heat can be recovered by the heat exchanger and the proposed hot input remains cold. assuming that the Pera’s testing had shown this to be the correct layout. creating an adjustable. No can be mixed with this as it has already been used. 4) enough.4 In conclusion. Thus the foreseen viability of our solution has increased dramatically. the pump uses more energy getting warmed water back to the shower than the energy saved. water For testing and display purposes. The removal of the pump means that any recovery of energy by the heat exchanger is 100% energy saved – our system does not use any electrical energy to recover the thermal energy. Simple testing has shown a secondary pump is not necessary – mains pressure will be sufficient for the circuit to flow.e. at minimum. to provide sufficient pressure. to ensure the cold mains travels through the heat exchanger and up to the mixing valve. 1 bar (see research). This is easily in an eventual saleable product. (See Figure 1. our final shower layout is this: Cold mains water travels through the heat exchanger and increases in temperature. 10 . we plan to use a pump. It removes the possibility that our system will INCREASE energy usage per shower – i. It reaches the mixing valve/ shower and is mixed with mains hot water.pressure is. Figure 1. where we do not have mains pressure and rely on gravity. We built a frame from wood (See Appendix D) over many hours that would be strong enough to hold up our water tanks and attached our shower unit and two 36L storage containers to it.) The group visited a builders’ merchant store and acquired 3m of 15mm copper pipe and various fittings for the plumbing of our own test rig. Drilling a hole in our shower tray (another storage container) and inserting (without creating leaks!) the sink fitting. compression-female thread tap connectors and tank flanges. using a mixture of 15mm copper piping and associated fittings and flexible hoses. Figure 2. 90 degree elbows. The team started with. The fittings included: taps. a sink fitting for our shower tray. We removed one unit from the frame and began to create our own specialised testing rig.1. See Figure 2. The completed test rig is shown below in Figure 2. two shower units attached to a frame that had been used for comparing brushed to brushless motors in showers. 22-15mm reducers. due to the limitations of our test rig. Connecting the right hand storage container (designated our cold water source) to first the pump. We also bought.1 We used this pre-made set up to measure the flow rate produced by the shower. We had to hand craft a reducer so that we were able to connect the sink to flexible hose. During our time at Loughborough University. at a later date. this same flow was not achieved. 3 way elbows.Implementation Creating our testing rig We began our implementation by gathering materials for creating a shower setup to test the efficiency of our recovery system. Connecting our ‘shower tray’ (and thus our waste water) to one end of the heat exchanger and then out to a waste bucket. using flexible hoses. we worked on the plumbing of the rig. Running water through the above assembly to detect leaks and then reassembling those parts of our plumbing. end stops (to act as tank drain cocks). then to the other end of the heat exchanger (so that we get efficient counter-current exchange) then out to the cold water input of the shower.2 11 . This involved: Connecting the left hand storage container (designated our hot water source) to the hot water input of the shower using 15mm copper piping and associated fittings. (Later. courtesy of Mark’s parents’ engineering work. it was found to be equal to the flow rate from regular mains. making fittings tighter and using PTFE tape as a sealant. Figure 2.2 Hot water source Cold water source Shower unit Shower tray with waste pipe Note: The heat exchanger and the pump are located behind the shower unit 12 . 3 1. To measure the temperatures of the water inside sections of copper piping (in the supply of cold water to the heat exchanger and.9 3.9 *all tests were completed with the washing machine hose at the same level as the heat exchanger.9 7.9 2.3 3. These were connected to a homemade PIC microcontroller for display.8 2.3 1.5 1 7.9 3. (PIC stands for programmable/peripheral interface controller. in the warmed water coming from the heat exchanger towards the shower unit) we inserted.2 2.1 2.9 7. After some research we found that while this is not the normal quoted ‘shower temperature’ this is actually the normal temperature of the shower water going down the drain.0 6.0 2.8 3.1 2.9 5. our most important measurement.9 5.0 6. The water that leaves the shower head is typically at 45˚C (4) but there is a 10˚C loss in temperature before the water reaches the drain.2 3.9 2.2 2.3 1.7 2.0 5.0 2. These show the efficiency of our heat exchanger. using epoxy.9 6.2 2. Table 2: Temperature measurements (all in C) These measurements are our core data. These measurements are focused around a temperature for shower water of 35˚C.3 1.) Flow rate – Between the heat exchanger and the cold water input to the shower unit.6 3.Results The quantities we had to measure throughout the experiment were: Temperature – At various points.9 7.1 6.9 7. They are all average values taken from at least three repeats. We have used thermal probes connected to a data logger to measure the temperatures of water in the exposed areas: The hot and cold water sources and the waste water in the shower tray.9 2. Using a flow rate meter connected to the same PIC Time – Using a lab stop-clock Table 1: Flow rate measurements Pum p N/A N/A Waste Feed* Heat Washing Machine Exchanger hose yes yes no N/A Pum p yes yes yes no no no Cold Feed* Heat Washing Machine Exchanger hose yes no no N/A yes yes yes no no N/A yes yes Flow Rate (litres/minute) 1 2 3 4 Averag e 2. thermocouples into modified TRV valves.9 Flow Rate (litres/minute) 2 3 4 Average 6.9 5.3 1. 13 .0 6.9 2. of cold (C) Time to full efficiency Temp. of 20 cold (°C) Time to 90 full efficiency Temp. of warmed water (°C) 10 20 20 21 30 21 40 21 50 22 60 22 70 23 80 23 90 24 100 24 110 24 120 24 130 24 140 24 150 24 160 24 (onwards) For 35C shower water Time (s) Average temp of warmed water (C) 10 16 20 16 30 18 40 20 50 21 60 23 70 24 80 25 90 25 100 25 110 26 120 26 130 27 140 27 150 28 160 28 (onwards) For 45C shower water Time (s) Average temp of warmed water (C) 10 22 20 23 30 23 40 24 50 25 60 27 70 30 80 32 90 33 100 34 110 35 120 35 130 35 140 35 150 35 160 35 (onwards) Temp.Shower water 25 30 35 40 45 Cold water source before HE 18 18 18 18 18 Warmed water after HE 24 27 29 31 33 Waste water after HE Increase in temperature on cold feed 6 9 11 13 15 Decrease in temperature on waste feed Table 3: Change in temperature recovery over time At the start of a shower. of cold (C) Time to full efficiency 16 150 18 110 Mathematical analysis of the empirical results (Table 1) 14 . They are the average of several measurements. For 25°C shower water Time (s) Average temp. These measurements were taken to time how long it takes for our system to reach maximum efficiency. The temperature of shower water would change as the experiment progressed. only cold water flows so recovery of heat is zero. so these should be considered accurate with an uncertainty of ±3˚C. We will use two equations: Bernoulli’s Equation and the continuity equation both of which are given below. Mathematical analysis of the empirical results (tables 2 and 3): 15 . Knowing that a depth of water of 10cm (the height under the shower tray) produces 0.31mbar 0. we can remove the gh value. we get: p (¿ ¿ 2− p1 ) 2 2 500 ( v 1 −v 2 ) =¿ We can then calculate that the pressure across the following components is: Heat Exchanger: Washing machine hose input: Washing machine hose output: Washing machine hose total: Negligible pressure drop 0.01 bar. g = gravitational field strength. By rearranging and cancelling out some of the rho values. we can calculate that we are losing about 15% of the pressure we would theoretically have just through the use of two washing machine hoses. We also know that since the Bernoulli Equation is equal to a constant. h = height lost/gained. v 21 p1 v 22 p 2 + = + 2 ρ1 2 ρ2 2 2 v 1 ρ1 ρ 2+2 p1 ρ2=v 2 ρ1 ρ2+2 p2 ρ1 We know that rho = 1000kg/m3 for water. These are both simplified versions of the true equations. we can then assume that the density does not change across the heat exchanger/ washing machine pipe.37mbar 0. The pipes can easily be changed so it is not a concern. These are often flexible hoses that are narrowed in places and are far longer than necessary. This is a reasonable assumption to make – temperature does not influence it greatly.We are trying to work out whether there is a pressure drop across the heat exchanger or washing machine hose and if so what its value is. Since h was limited to 0 (we tried as much as possible to do so). 2 v p + + gh=constant 2 ρ p1 A 1=p 2 A2 Where: v = velocity. we can put it in a similar form to the continuity equation.68mbar Therefore we can come to the conclusion that we do not need a pump in our system even if our prototype implies that we do because it is not our heat exchanger that is causing a large decrease in pressure it is in fact our pipes and their fittings. p = pressure. ρ = density. A = cross-sectional area. the total energy saved in a year becomes**: Total energy saved =270 J × 103 × 6 × 4 ×365 Total energy saved =2365200000 J ≈ 2. Assuming a 35˚C shower run for 7 minutes. The cost benefit to the consumer of having a heat exchanger in place 4. Therefore the payback time of the heat exchanger system The main equation we will use for efficiency: q=mc ∆ T Where: m = mass of water (g).4 ×109 =670 kWh 3. Cold feed energy in (kJm-1) Waste water energy out (kJm-1) Efficiency* (%) 25˚C 150 30˚C 220 35˚C 270 40˚C 320 45˚C 370 ¿ × 100 Waste water energy out ¿ Efficiency=¿ Cold feed energy ∈ Therefore the average efficiency of the heat exchanger is: ____ MEASUREMENTS ARE NEEDED The average time taken for the heat exchanger to reach maximum efficiency is (taken from table 3): 120s or 2 minutes. 4 times a day by a family of 4. c = specific heat capacity (4.We now wish to calculate: 1.6× 106 Utility prices state that for the first 500 kWh they cost 12p each. The time taken for the heat exchanger to reach maximum efficiency 3. fig .) 100 16 . The efficiency of our heat exchanger 2.18kJ -1g-1 for water). The energy required to heat the water on the cold feed to the measured increase in temperature (see table 2) at different shower temperatures and the energy lost by the waste water at different shower temperatures are shown below.4 × 109 J Total energy saved = 2. ΔT = change in temperature (˚C). q = energy change (J).00(¿ 2 sig . Therefore the conversion from kWh saved to money saved is as follows: Total money saved= 670 ×12 p =£ 80. Since we know the flow rate (l/m) we can simply say this is equal to kg/m and then be able to calculate energy transferred per minute. The energy saved in that is equal to one minute at full efficiency. 1 hour and 12 minutes.9lmin-1. So. 17 . then the payback time for the heat exchanger system is: 5 months 1 week. Cold water from mains (18˚C) Shower Temperature (35˚C) Heating therefore requires 420kJmin-1. **Due to the time taken for the heat exchanger to reach maximum efficiency being 2 minutes. you have to take away two minutes from the time the shower is running because the heat exchanger is not recovering all the energy at this point.9lmin-1.Given that our heat exchanger cost about £34. still needed to heat water: 150kJmin-1 at a flow rate of 5. at a flow rate of 5. leaving you with a 5 minute shower.90. below is the normal energy requirements for using a shower per minute. To put our savings into context. However we can assume that efficiency increases at a linear rate and hence taking the average of this we can say that the heat exchanger runs for 2 minutes at half the efficiency. thus we can add 1 minute to 5 minutes giving us the value shown above for a 6 minute shower.9lmin-1 Therefore using these calculations we come up with a rudimentary calculation for the efficiency of our entire system: Energy saved by HE ×100 = Efficiency for whole system Total energy used by a normal shower This equation means that if the efficiency were 100%. Cold water from mains (18˚C) After HE temperature (29˚C) Shower Temperature (35˚C) Energy saved by HE: 270kJmin-1 at a flow rate ofEnergy 5. How much energy saved is shown below. our system saves a considerable amount of energy. then we would never need to heat any water for a running shower. in the heat exchanger and in any pumping systems.Efficiency for whole system= 270 kJ min−1 ×100 =64 420 kJ min−1 This value takes into account all loses in the shower. in the pipes. This shows that our system compared to other energy saving systems is very efficient. 18 . using a power drill.Display Model We decided to develop our test rig before it goes on display. cut a hole large enough for the hot and cold feed pipes of the shower to fit through. cutting tiles to the appropriate dimensions (see Appendix E (2)). See Appendix E (1) We tiled the plywood surfaces and the top of the frame using spare bathroom tiles and tile adhesive from a property renovation. See Appendix E (3) Tiled display model after grouting.) Holes were drilled in the sides to allow piping to enter and leave. remember – will sit outside this frame. See Figure 3. including a trim of smaller tiles and grouting all of this. leaving the wooden frame bare. we: Disassembled the plumbing completely. making it more compact and improving its aesthetics. It was later wiped down to remove excess grout. this frame simulating the space under a shower tray required to house piping and our heat exchanger. This enabled us to measure out and affix three plywood boards to the sides and front of the frame. (The pump – needed only for the display.1 19 . With access to only our own resources. The plywood was first painted white. a box for shower tray simulation was being created. The shower tray storage container rests on top of a rectangle of interlocking plywood pieces. We then.1 Meanwhile. Figure 3. Normally one would expect the flow rate to be closer to 10lmin-1 20 .Conclusions Will/max remember to write about limitations of our prototype system. for example: A major limitation of these calculations is that the flow rate of our shower is about half that of a normal shower. in reality. This study has been cited by BBC news and Which?. In addition. be pumping cold water through the heat exchanger. However. (2) John Cox.co. this will not have affected our results.unilever. lending it reliability.Recommendations Use a larger drainage pipe for shower tray. not wide enough to remove water from the shower tray as needed to prevent pooling. Bibliography (1) http://www. plumber 21 .600 showers by Unilever.uk/media-centre/pressreleases/2011/sustainableshowerstudy. We used a sink fitting.aspx A study of 2. our waste pipes were 32mm or 20mm. Use a more powerful pump to better simulate the mains pressure that would. net/recoh-tray-rt-1/ (4) Average temperature statistic???? (5) William Dowell.(3) http://www. “Week 5 Spring Term” refers to 02/02/15 to 09/01/15 22 . physics technician at Oakham School Appendices Appendix A: An example of a weekly time plan.showersave. Appendix B: Insert Gantt Chart 23 . Appendix C: Diagrams to show the three systems Shower Save propose for the use of the RecohTray RT-1 24 . Appendix D: A CAD model of the wooden frame used as the skeleton for our testing rig Appendix E: Display model photos 1) 25 . The tiles were cut so that the hole was not covered.The hole bored in the plywood to allow for plumbing. 2) 2) 26 . 2) 3) The whole team worked on tiling – it required many man hours. Painting parts of the plywood shower tray frame 27 .