ContentsAcknowledgements.................................................................................................................1

Summary.................................................................................................................................2

Time Management..................................................................................................................3

Weekly plans.......................................................................................................................3

Introduction.............................................................................................................................4

Our Company – Pera...........................................................................................................4

Our School and Team.........................................................................................................4

Situation..............................................................................................................................4

Brief....................................................................................................................................5

Research..................................................................................................................................6

Analysis of current products...............................................................................................6

Showers...............................................................................................................................6

Domestic Plumbing.............................................................................................................7

Plan.........................................................................................................................................8

Implementation.......................................................................................................................9

Creating our testing rig.......................................................................................................9

Results...............................................................................................................................11

Display Model.......................................................................................................................17

Conclusions...........................................................................................................................18

Recommendations.............................................................................................................19

Bibliography.........................................................................................................................20

Appendices............................................................................................................................21

AcknowledgementsManilka 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, providing advice (and common sense!) throughout and critiquing this report

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Summary

2

Time Management

Weekly plansMark 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.

Gantt ChartSee Appendix B

3

Introduction

Our Company – PeraPera is a company with three main branches, these being Pera Technologies, Pera Consulting and Pera Training, offering, respectively, Product Development, Government Services and Workplace Training.

It was Pera Technologies that provided us with our task and their support. They are a leading product development contractor and work with companies across Europe, of all sizes. Furthermore, they work on a huge range of products and have specialised engineers covering many areas of physics and mechanics. Once a product is designed, tested and approved, Pera Technologies can also construct supply chains of partners to get the product onto the market, from manufacturing through to the consumer.

Pera Technologies has many groups of staff to tackle their extremely varied work.Our link engineer, Manilka Abeysuriya, works in their Informatics and PMM groups and so covers With informatics: control systems, GUI design, desktop/web applications, databases With PPM: Modelling (structural, thermal, fluids) and microwave work (heating/drying, material processing, communications, radar)

Our School and TeamOakham 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. It is located in Oakham, Rutland.

The team is made up of four students, all currently studying AS level physics: Harry Smith, Mark Pollock, Will Alexander and Max Jones. Our supporting teacher is physicist Miss Hannah Williams.

SituationNote: Bracketed numbers indicate the source used, details of which are found in the bibliography.

15 – 20% of domestic energy is used for heating water for ablution processes. This is due to the large volumes heated and because water has a high specific heat capacity, meaning a lot of energy is required to raise its temperature. (Around 4.18J is needed to heat 1 gram (and thus 1cm) of water by 1C.) In showers, this heat is experienced briefly and some is imparted on the air and the user, but the majority remains in the waste water and is lost down the drain.

A heat exchanger can be used to recycle some of this heat. A heat exchanger runs two pipes made of a good thermal conductor alongside each other. When a hot fluid flows in one pipe and a cold fluid flows in the other, heat is transferred by conduction to the colder fluid. To increase the efficiency of a shower (from 0% - usually no heat is recycled), the hot waste water is run in one pipe while cold,

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mains water is run through the other, becoming slightly heated. This warmer water is directed to the shower and mixed with the hot input. This reduces the amount of hot, boiler water required per shower, thereby reducing the energy used.

Pera had already been experimenting with this idea using different configurations to determine whether this is a viable option for domestic use. They wanted us to take up the project and - as hopefully we would look at it from a different point of view - find potential improvements to their initial concept.

The end product is desirable as it provides a way to reduce the large cost of showering; the typical UK home spends ₤416 per year on showers, shooting to ₤918 if a power shower is used. On a larger scale, 5.3% of the UK’s energy is used to heat water and any reduction in this could have huge positive environmental impacts, namely, reduction in CO2 emissions, as fossil fuels are burnt to either directly heat water or to create the electricity used to heat water. (1)

BriefWe have been tasked with testing the viability of the method of re-using the hot water from showers using heat exchangers. We must find out if the energy recouped is too small to warrant the cost of a heat recovery system. Two separate costs need to be considered:

1) The cost of the system on its own, to be fitted when new showers are installed2) The cost of the system plus the cost of retrofitting it to existing showers

Ideally, we want a system where this second set of costs is outweighed by the savings of the system.

To do this, we must design a heat recovery system (that should be retrofit-able) and then create a method of testing its energy savings.

5

Research

How a heat exchanger worksWe started out, presumably like the majority of the public, unaware of what exactly a heat exchanger is or how it works.

Analysis of current productsRecoh-Tray, RT-1 by Shower Save: A large, circular heat exchanger system. They propose three systems for their heat exchanger: A) Mains water, having been warmed by the heat exchanger travels to both the shower and the boiler with a claimed 47% efficiency. B) Warmed water travels just to the shower with a claimed 39% C) Warmed water travels just to boiler with a claimed 41% efficiency. See Appendix C for flow diagrams of their three systems.

However, system A involves removing a mains water feed from one of the shower or boiler and directing one feed into both appliances, on top of inserting the heat exchanger into the system. This is much more labour intensive than either B or C and will raise the installation price, increasing the pay back time, for a reasonably small increase in efficiency. This reduces the appeal of the product as its peak ability may not be seen by many users who, for cost reasons, use systems B or C.

Furthermore, 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. FIGURES??? Doubt as to their claimed sales figures is furthered on this site: http://www.wholebuild.co.uk/microsite/shower-heat-exchange-and-recovery-systemWho claim that using a string of another of Shower Save’s products, the Recoh Vert RV-3 they have created a 45-50% efficient system, while Shower Save claim a rating of 66% efficiency for one of these. This is improbable, given the nature of heat exchangers: they divide heat between two water feeds, so the output feeds should each have 50% of the heat at best.

Cost: £680.00 (not including labour) (plus £216.89 - £294.03 for a BETTE shower tray if your own does not accommodate the Recoh Tray.)

Also on the market are various

ShowersTypes:

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As mentioned in the situation section, regular and power showers use very different amounts of water. A typical shower (8 minutes long) using a regular shower uses 62 litres (1), while a power shower uses 136 litres (this second figure is almost twice as much a bath) (1).

Use: Daily usage – The average shower length is 8 minutes. Total usage depends on the number of people using the shower and the number of showers they have per day. Greatest savings will come with the greatest use of a shower. (1)Average shower temperatures – Between 35 and 40C (based on internet research (4) and the team’s own recordings). We will test a range of temperatures and record the efficiency of the system at each.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 - 60C (2)

Parameters: Shower tray depth – 100/90/6 cm (2) Therefore we have very limited space with which to work with. Quite possibly, for an eventual product, a custom built heat exchanger may need to be developed.Waste pipe diameter – 40mm diameter pipe (Various plug diameters, 40, 50 or 90, but almost all lead to a 40mm waste pipe) (2)

Domestic PlumbingPressure: 1 bar gauge pressure is certified by the nation’s water companies. However, pressures in excess of 4 bar are usual. (2) However, the 1 bar minimum is not assured for apartment blocks as the height water is required to be raised diminishes the pressure. Our final solution may need to be adapted for use in such circumstances. (5)Fittings:

As there is a plethora of different types of domestic plumbing fittings, we were quite lucky that local supply dictated that only 'Yorkshire joint' style, or Conex Compression fit were available. As the laboratory that we were in for the majority of the plumbing did not have blowtorch facilities, then we were restricted to compression fit fittings. A diagram of a Yorkshire joint versus a Compression fitting is below:

(PICTURES TO BE TAKEN)

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Figure 1.1

Figure 1.2

Plan

The initial flow diagram for the system Pera have provided us is seen in Figure 1.1.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. 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 for a shower. However, we have found a number of problems with the company’s original ideas.

Firstly, it appears to lack a mains hot water input, and while probably created assuming that “mains water supply” covers both hot and cold, we feel this is an over-simplification of the diagram. If Figure 1 was followed blindly, the shower would only ever use cold water, meaning no heat can be recovered by the heat exchanger and the proposed hot input remains cold. (Mains cold water, on average, has a temperature of 15°C, creating one very cold and undesirable shower!)

Our initial solution was to have a hot input straight from mains to the mixing valve, and a cold input that travels through the heat exchanger, gaining heat in the process that joins the hot input pipe before the mixing valve. See Figure 1.2. Therefore the ‘cold’ is already warmed slightly and as a result less hot water has to be used. However, there is one major flaw to this layout. Due to all cold water passing through the heat exchanger, the longer the shower runs, the hotter the cold input gets as a result of increasingly hot shower output, due to increased cold input temperature. Eventually, the temperature of the cold input will equal roughly half that of the hot input. No cold water can be mixed with this as it has already been used, creating an un-adjustable, scalding hot shower up to 60 degrees Celsius. Also, the lack of a cold input causes the shower pump to work too hard to draw in water that isn’t there, potentially damaging some models of shower.

Our solution is similar to Harry’s; a hot input straight from mains to the mixing valve, and a cold input that travels through the heat exchanger, gaining heat in the process. See Figure 1.3. Therefore the ‘cold’ is already warmed slightly and as a result less hot water has to be mixed in to provide normal shower temperature. This means less heat is wasted, meaning less energy is wasted and the shower is more efficient.

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Figure 1.3

Figure 1.4

Our other problem with the Pera diagram is the presence of an additional pump after the heat exchanger. In fact, at first we hadn’t thought about this, assuming that the Pera’s testing had shown this to be the correct layout. It wasn’t until we tested the flow rate of water through our heat exchanger that we realised a pump wasn’t necessary. Using a simple siphoning process, we have established that flow through the heat exchanger is almost unrestricted. This also worked (despite the manufacturer’s instructions) regardless of what orientation the heat exchanger was in. Mains water pressure is, at minimum, 1 bar (see research). This is easily enough, in an eventual saleable product, to ensure the cold mains water travels through the heat exchanger and up to the mixing valve. 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. It removes the possibility that our system will INCREASE energy usage per shower – i.e. the pump uses more energy getting warmed water back to the shower than the energy saved. Thus the foreseen viability of our solution has increased dramatically. (See Figure 1.4)

For testing and display purposes, where we do not have mains pressure and rely on gravity, we plan to use a pump, to provide sufficient pressure.

In conclusion, our final shower layout is this: Cold mains water travels through the heat exchanger and increases in temperature. It reaches the mixing valve/ shower and is mixed with mains hot water. Simple testing has shown a secondary pump is not necessary – mains pressure will be sufficient for the circuit to flow.

Implementation

Creating our testing rigWe began our implementation by gathering materials for creating a shower setup to test the efficiency of our recovery system.

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The team started with, courtesy of Mark’s parents’ engineering work, two shower units attached to a frame that had been used for comparing brushed to brushless motors in showers. See Figure 2.1. We used this pre-made set up to measure the flow rate produced by the shower, it was found to be equal to the flow rate from regular mains. (Later, due to the limitations of our test rig, this same flow was not achieved.)

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. The fittings included: taps, 3 way elbows, 90 degree elbows, end stops (to act as tank drain cocks), 22-15mm reducers, compression-female thread tap connectors and tank flanges.

We also bought, at a later date, a sink fitting for our shower tray.

We removed one unit from the frame and began to create our own specialised testing rig. 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. During our time at Loughborough University, we worked on the plumbing of the rig. 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. Drilling a hole in our shower tray (another storage container) and inserting (without

creating leaks!) the sink fitting. We had to hand craft a reducer so that we were able to connect the sink to flexible hose.

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.

Connecting the right hand storage container (designated our cold water source) to first the pump, 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, using a mixture of 15mm copper piping and associated fittings and flexible hoses.

Running water through the above assembly to detect leaks and then reassembling those parts of our plumbing, making fittings tighter and using PTFE tape as a sealant.

The completed test rig is shown below in Figure 2.2

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Figure 2.1

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

Figure 2.2

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ResultsThe quantities we had to measure throughout the experiment were:

Temperature – At various points. 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. To measure the temperatures of the water inside sections of copper piping (in the supply of cold water to the heat exchanger and, our most important measurement, in the warmed water coming from the heat exchanger towards the shower unit) we inserted, using epoxy, thermocouples into modified TRV valves. These were connected to a homemade PIC microcontroller for display. (PIC stands for programmable/peripheral interface controller.)

Flow rate – Between the heat exchanger and the cold water input to the shower unit. Using a flow rate meter connected to the same PIC

Time – Using a lab stop-clock

Table 1: Flow rate measurements

Waste Feed* Flow Rate (litres/minute)Pump Heat Exchanger Washing Machine hose 1 2 3 4 AverageN/A yes yes 2.8 2.9 3.0 2.9 2.9N/A no N/A 3.2 3.6 3.8 3.3 3.5

Cold Feed* Flow Rate (litres/minute)Pump Heat Exchanger Washing Machine hose 1 2 3 4 Averageyes yes no 7.0 6.9 7.1 7.0 7.0yes no N/A 6.9 7.0 6.9 6.9 6.9yes yes yes 5.7 5.9 6.0 5.9 5.9no yes no 2.2 2.1 2.2 2.1 2.2no no N/A 2.3 2.3 2.3 2.3 2.3no yes yes 1.9 1.9 1.9 1.9 1.9

*all tests were completed with the washing machine hose at the same level as the heat exchanger.

Table 2: Temperature measurements (all in C)These measurements are our core data. These show the efficiency of our heat exchanger. They are all average values taken from at least three repeats. These measurements are focused around a temperature for shower water of 35˚C. 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. 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.

Shower water Cold water Warmed water Waste water Increase in Decrease in

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source before HE

after HE after HE temperature on cold feed

temperature on waste feed

25 18 24 630 18 27 935 18 29 1140 18 31 1345 18 33 15

Table 3: Change in temperature recovery over timeAt the start of a shower, only cold water flows so recovery of heat is zero. These measurements were taken to time how long it takes for our system to reach maximum efficiency. They are the average of several measurements. The temperature of shower water would change as the experiment progressed, so these should be considered accurate with an uncertainty of ±3˚C.

For 25°C shower water For 35C shower water For 45C shower waterTime (s) Average temp. of

warmed water (°C)Time (s) Average temp of

warmed water (C)Time (s) Average temp of

warmed water (C)10 20 10 16 10 2220 21 20 16 20 2330 21 30 18 30 2340 21 40 20 40 2450 22 50 21 50 2560 22 60 23 60 2770 23 70 24 70 3080 23 80 25 80 3290 24 90 25 90 33100 24 100 25 100 34110 24 110 26 110 35120 24 120 26 120 35130 24 130 27 130 35140 24 140 27 140 35150 24 150 28 150 35160 (onwards)

24 160 (onwards)

28 160 (onwards)

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Temp. of cold (°C)

20 Temp. of cold (C)

16 Temp. of cold (C)

18

Time to full efficiency

90 Time to full efficiency

150 Time to full efficiency

110

Mathematical analysis of the empirical results (Table 1)

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. We will use two equations: Bernoulli’s Equation and the continuity equation both of which are given below. These are both simplified versions of the true equations.

v2

2+ p

ρ+gh=constant

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p1 A1=p2 A2

Where: v = velocity, p = pressure, ρ = density, g = gravitational field strength, h = height lost/gained, A = cross-sectional area.

Since h was limited to 0 (we tried as much as possible to do so), we can remove the gh value. We also know that since the Bernoulli Equation is equal to a constant, we can put it in a similar form to the continuity equation.

v12

2+

p1

ρ1

=v2

2

2+

p2

ρ2

v12 ρ1 ρ2+2 p1 ρ2=v2

2 ρ1 ρ2+2 p2 ρ1

We know that rho = 1000kg/m3 for water, we can then assume that the density does not change across the heat exchanger/ washing machine pipe. This is a reasonable assumption to make – temperature does not influence it greatly. By rearranging and cancelling out some of the rho values, we get:

500 (v12−v2

2 )=( p¿¿2−p1)¿ We can then calculate that the pressure across the following components is: Heat Exchanger: Negligible pressure dropWashing machine hose input: 0.31mbarWashing machine hose output: 0.37mbarWashing machine hose total: 0.68mbar

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. These are often flexible hoses that are narrowed in places and are far longer than necessary. The pipes can easily be changed so it is not a concern.

Knowing that a depth of water of 10cm (the height under the shower tray) produces 0.01 bar, 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.

Mathematical analysis of the empirical results (tables 2 and 3):

We now wish to calculate:1. The efficiency of our heat exchanger2. The time taken for the heat exchanger to reach maximum efficiency3. The cost benefit to the consumer of having a heat exchanger in place4. Therefore the payback time of the heat exchanger system

The main equation we will use for efficiency:

q=mc ∆ T

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Cold water from mains (18˚C)

Heating therefore requires 420kJmin-1, at a flow rate of 5.9lmin-1.

Shower Temperature (35˚C)

Where: m = mass of water (g), c = specific heat capacity (4.18kJ-1g-1 for water), q = energy change (J), ΔT = change in temperature (˚C). 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 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.

25˚C 30˚C 35˚C 40˚C 45˚CCold feed energy in (kJm-1) 150 220 270 320 370Waste water energy out (kJm-1)Efficiency* (%)

¿ Efficiency=Cold feed energy∈ ¿Waste water energy out

× 100%¿

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.

Assuming a 35˚C shower run for 7 minutes, 4 times a day by a family of 4, the total energy saved in a year becomes**:

Total energy saved=270 J ×103 ×6× 4 × 365

Total energy saved=2365200000 J ≈ 2.4 ×109 J

Total energy saved=2.4 × 109

3.6 ×106 =670kWh

Utility prices state that for the first 500 kWh they cost 12p each. Therefore the conversion from kWh saved to money saved is as follows:

Total money saved=670 ×12 p100

=£ 80.00(¿2 sig . fig .)

Given that our heat exchanger cost about £34.90, then the payback time for the heat exchanger system is: 5 months 1 week, 1 hour and 12 minutes.

To put our savings into context, below is the normal energy requirements for using a shower per minute.

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Cold water from mains (18˚C) Shower Temperature (35˚C)After HE temperature (29˚C)

Energy saved by HE: 270kJmin-1 at a flow rate of 5.9lmin-1.Energy still needed to heat water: 150kJmin-1 at a flow rate of 5.9lmin-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, leaving you with a 5 minute shower. 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. The energy saved in that is equal to one minute at full efficiency, thus we can add 1 minute to 5 minutes giving us the value shown above for a 6 minute shower.

So, our system saves a considerable amount of energy. How much energy saved is shown below.

Therefore using these calculations we come up with a rudimentary calculation for the efficiency of our entire system:

Energy saved by HETotalenergy used bya normalshower

×100 %=% Efficiency for whole system

This equation means that if the efficiency were 100%, then we would never need to heat any water for a running shower.

% Efficiency for whole system=270 kJ min−1

420 kJ min−1 ×100 %=64 %

This value takes into account all loses in the shower, in the pipes, in the heat exchanger and in any pumping systems. This shows that our system compared to other energy saving systems is very efficient.

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Display ModelWe decided to develop our test rig before it goes on display, making it more compact and improving its aesthetics. With access to only our own resources, we: Disassembled the plumbing completely, leaving the wooden frame bare. This enabled us to measure out and affix three plywood boards to the sides and front of

the frame. We then, using a power drill, cut a hole large enough for the hot and cold feed pipes of the

shower to fit through. See Appendix E (1)

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We tiled the plywood surfaces and the top of the frame using spare bathroom tiles and tile adhesive from a property renovation, cutting tiles to the appropriate dimensions (see Appendix E (2)), including a trim of smaller tiles and grouting all of this. See Figure 3.1

Meanwhile, a box for shower tray simulation was being created. The shower tray storage container rests on top of a rectangle of interlocking plywood pieces, this frame simulating the space under a shower tray required to house piping and our heat exchanger. (The pump – needed only for the display, remember – will sit outside this frame.) Holes were drilled in the sides to allow piping to enter and leave. The plywood was first painted white. See Appendix E (3)

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. Normally one would expect the flow rate to be closer to 10lmin-1

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Figure 3.1Tiled display model after grouting. It was later wiped down to remove excess grout.

Recommendations Use a larger drainage pipe for shower tray. We used a sink fitting. In addition, our waste pipes

were 32mm or 20mm, not wide enough to remove water from the shower tray as needed to prevent pooling. However, this will not have affected our results.

Use a more powerful pump to better simulate the mains pressure that would, in reality, be pumping cold water through the heat exchanger.

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Bibliography(1) http://www.unilever.co.uk/media-centre/pressreleases/2011/sustainableshowerstudy.aspx

A study of 2,600 showers by Unilever. This study has been cited by BBC news and Which?, lending it reliability.

(2) John Cox, plumber(3) http://www.showersave.net/recoh-tray-rt-1/ (4) Average temperature statistic????(5) William Dowell, physics technician at Oakham School

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AppendicesAppendix A: An example of a weekly time plan. “Week 5 Spring Term” refers to 02/02/15 to 09/01/15

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Appendix B: Insert Gantt Chart

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Appendix C: Diagrams to show the three systems Shower Save propose for the use of the Recoh-Tray RT-1

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Appendix D: A CAD model of the wooden frame used as the skeleton for our testing rig

Appendix E: Display model photos

1)

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2)

25

2)

The hole bored in the plywood to allow for plumbing. The tiles were cut so that the hole was not covered.

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2) 3)

Painting parts of the plywood shower tray frame

The whole team worked on tiling – it required many man hours.