Pressure Shower

This invention of mine makes use of the fact that water held under pressure boils at a higher temperature. This enables a small quantity of water to be kept ‘on the boil’ and mixed with cold water at shower time. Mathematically I have demonstrated that it can be used to adequately provide a shower off a 13amp mains supply. A 13amp mains supply is often available whereas the more typical 32amp supply, required for an electric shower, often involves too much disruption to install. Additionally I have mathematically shown how a 32amp shower can be improved by using the same principle of water held under pressure. In the latter case I have demonstrated how, theoretically, the water flow of a 32amp electric shower can be increased to that of a power shower.

The following is the patent, filed in 2003. As it could potentially reduce carbon use, you are free to develop this idea.

1.1 Background

Two problems exist with a typical electric shower. Firstly an electric shower typically requires a 32amp electric supply which is often impractical or too disruptive to install. Secondly a typical 32amp electric shower is often criticised for not having sufficient rate of flow of water through the shower.

This invention makes use of a pre-heated fluid, typically water but not restricted to being water, to either fully provide, or to enhance the performance, of a shower. The fact that a fluid when held under pressure has an increased boiling point is used to increase the performance.

1.2 Mains Electric (typically 13amp) Pressure Shower

A typical electric shower requires a 32amp electrical supply to be able to allow a shower to be taken at adequate comfortable temperature and water flow. In some houses it is either impractical, or too disruptive, to install a 32amp cable to the point of where a shower is required. However, often it is the case that a 13amp electric supply is available near to where the shower is required.

At present a shower running off a13amp supply does not generate enough heated water for a user to enjoy a comfortable shower.

In this description, by way of example, a comfortable shower will be described as one that supplies 90 grams of water per second heated to 36.8 degrees centigrade (typical body temperature).

A 13amp electrical supply will generate 3120 watts. This equates to 3120 Joules per second of power. The specific heat of water is 4.186 Joules per gram per degree centigrade rise. In other words it takes 4.186 Joules to raise 1 gram of water by 1 degree centigrade. Given a comfortable shower flow is 90 grams of water per second, then it follows that a supply of 3120 Joules per second will raise 90 grams of water per second by:

3120/(4.186*90) = 8.3 degrees centigrade.

Given that ambient water temperature is typically 20 degrees centigrade then it follows that a 13amp supplied shower would raise the temperature of the water to 28.3 degrees centigrade. Given a comfortable shower requires the water temperature to be 36.8 degrees centigrade this is somewhat inadequate.

Conversely the shower could be ran at 36.8 degrees centigrade with a much reduced flow rate. The grams of water per second that can be raised in temperature by 16.8 degrees centigrade (the difference between 36.8 degrees centigrade and ambient) can be calculated as:

3120/(4.186*16.8) = 44.4 grams of water per second

Either way we can conclude that a standard 13amp-supplied shower, for instantaneous water heating, is inadequate.

At normal atmospheric pressure pure water boils at 100 degrees centigrade. As the pressure increases water will boil at a higher temperature. In part this invention employs this fact to enable a quantity of water, in liquid form, to be kept at above 100 degrees centigrade. Further this water will be used to either mix with or heat, by means of a heat exchanger, incoming cold water to create a shower running off a smaller electrical supply e.g. 13amp at 240 Volt AC.

Where the shower water is heated by a heat exchanger the quantity of fluid held to be heated, when the shower is not in use, does not have to be water. Something with a higher specific heat than water could be used.

A limitation of this first stage of the invention is the fact that the pre-heated water will run out during the shower. However an average shower requires 30 litres of water (information supplied by Southern Water energy saving WEB site article under www.southernwater.co.uk) and with careful design this invention could generate a supply of 30 litres at 90 grams per second heated to 36.8 degrees centigrade where the ambient temperature is 20 degrees centigrade. It should be noted that 30 litres of water supplied at 90 grams per second would give a shower duration of 5 minutes and 33 seconds. Beyond that time it is proposed that this invention would allow the shower to continue by employing instantaneous heating whereby the flow rate, while maintaining the temperature of 36.8 degrees would be reduced to 44.4 grams per second as given above.

For illustrative purposes the following shows how this invention could be designed to give a theoretical maximum of a shower lasting 6 minutes and 31 seconds with water heated to 36.8 degrees centigrade supplied at 90 grams per second. In this example the pre-heated water is 3 litres held at 120 degrees centigrade. This temperature has been chosen for illustrative purposes because it is the typical temperature of a domestic pressure cooker.

The deployable energy stored in the 3 litres of water is:

(Water Temperature – Ambient Temperature)

* Weight in grams of water

* Specific heat of water

This equates to:

(120 – 20) * 3000 * 4.186 = 1255800 Joules.

We now calculate how much water this could heat from 20 degrees (ambient temperature) to 36.8 degrees:

1255800 = (36.8-20)*grams of water*4.186

This gives the grams of water to be 17857.142

At a flow rate of 90 grams of water a second this would give a supply of water at 36.8 degrees for 198.4 seconds. As yet we have not included the fact that the pre-held water will be subject to reheating during the showering phase. This will make the showering phase greater than 198.4 seconds. We will return to this but in the meantime we will use an alternative way to confirm that if we took 90 grams of water per second for 198.4 seconds we’d have 17857.142 grams of water at 36.8 degrees centigrade. If we take enough water to mix with the 3 litres (3000 grams) at 120 degrees centigrade we’d require 14857.142 grams of cold water. This 14857.142 grams of water at 20 degrees centigrade (ambient temperature) added to the 3000 grams of pre-heated water would yield 17857.142 grams. What would the mean temperature become per gram of water?

((14857.142* 20) + (3000 * 120))/(14857.142 + 3000) = 36.8

This equates to 36.8 degrees centigrade which indicates that the formula holds up.

As mentioned above the 13amp supply (by way of a 3120 watt element) would still be heating the 3 litres, whilst the 3 litres of water heated the shower output, then the temperature of the shower outlet would be maintained for longer than the 198.4 seconds calculated above. We can recalculate how long an initial 3 litres of 120 degrees water will last when trying to supply at 36.8 degrees at 90 grams per second whilst being reheated by a 13amp element. The time is in T seconds:

Total power available = Heat energy supplied to shower water

The Total Power Available (TPA) can be expressed as:

TPA = Initial energy held by 3 litres of water at 120 degrees centigrade

+ Power Available During the shower Duration

TPA = ((120 – 20) * 3000 * 4.186) + (T * 3120)

TPA = 1255800 + 3120T

The amount of energy required to heat the shower water (90 grams of water per second for T seconds raised from 20 to 36.8 degrees centigrade) will be:

(36.8-20)*T*90*4.186

Thus we can conclude that:

1255800 + 3120T = (36.8-20)*T*90*4.186

1255800 + 3120T = 6329.232T

T = 391.3 seconds.

T = 6 minutes and 31 seconds.

Thus we have shown that the theoretical maximum shower duration for a 3 litre pre-heated (to 120 degrees centigrade) water volume discharged at 90 grams of water per second at 36.8 degrees centigrade is 6 minutes and 31 seconds. This is approximately one minute longer than what Southern Water define as an average shower. (Their figure is based on an average shower consuming 30 litres of water which when discharged at 90 grams per second would last for 5 minutes and 33 seconds). It should be restated that once the 6 minutes and 31 seconds were up the shower could continue at the same temperature but a reduced flow of 44.4 grams of water per second.

The following table details the maximum theoretical shower times based on the pressure rating and a pre-heated water volume of 3 litres being discharged at 90 grams per second:

Again it should be noted that when the shower time has expired the shower could continue at the same temperature but a reduced flow of 44.4 grams of water per second.

It should be noted, from the above table, that after the shower the initial 3 litres of water will need to be reheated. For the example, given above, of the 3 litres of water heated to 120 degrees this would be 6 minutes and 42 seconds. This is probably adequate for a multi person household where the first user would still be occupying the shower space to dry themselves.

It should be noted that the stored pre-heated water should be stored within an insulated container.

1.3 Power Shower Water Pressure From A Typical Electric Shower

For certain consumers the main downside of an electric shower is that it lacks sufficient water flow. This is as a consequence of the rate at which the electric supply, typically 32amp, can heat sufficient quantities of water.

If the shower contained a pre-heated supply of water then this could be used as a power boost for part of the shower cycle. This would be useful for rinsing shampoo from hair or for the revitalising effects that a more powerful shower offers.

As a current electric shower can be regarded as adequate then any increase in water flow will be a bonus. Therefore it follows that a pre-heated supply of water, held within the shower, does not necessarily have to be kept under pressure to give a greater temperature and hence greater water flow when mixed with incoming cold water. However, the following calculations give the water flow increases for both water held under pressure and water held at normal atmospheric pressure as there are benefits in still maintaining the water under pressure.

It should be noted that an assumption is being made that the cold water will have sufficient pressure to be able to force this additional water through at the desired rate. If it is found that, for example, the cold water pressure is inadequate then this can either be relieved by the use of a pump or the user can accept a not so high flow rate during the power shower cycle.

The first thing to consider is the increase in water flow required to give the effect of a power shower for part of the showering cycle. The user would either select this, by way of example, using a button or a control knob. The Three Valleys Water web site (www.3valleys.co.uk) agrees with the Southern Water web site that a standard electric shower uses about 30 litres of water. It gives further information that a power shower uses 60-100 litres. For the sake of this illustration we will take a power shower to use 90 litres and therefore be three times the water flow as an electric shower. As we took the flow rate of a standard electric shower to be 90 grams per second we need to increase this to 270 grams per second. This indicates that the pre-heated supply of water needs to supply sufficient water to mix with the cold water supply to create180 grams per second at 36.8 degrees centigrade.

The following table is a calculation of the amount of time a power shower cycle could be engaged during a normal electric shower. Note that as the stored hot water would be heated by the same power supply, and optimally the same heating element, as the heating of the normal electric shower this phase can only be a one off during the shower. The exception to this would be where the shower user chooses a lower temperature during normal showering and spare heating capacity could be fed through to reheat the stored water.

At first sight these base numbers may appear a little small. But if we stay conservative and say that only a 120 degrees centigrade pressure heater is practical but assume that 2 litres of stored water is practical and furthermore take it that doubling the water flow of an electric shower, instead of tripling it as in the above figures, is satisfactory then the length of the power shower cycle would be two minutes twelve seconds.

Furthermore a final implementation of this may well offer a control knob to allow the shower user to adjust the power of the shower boost. It may also be possible for this to be controlled, by the user, such that the increased pressure is enjoyed for the full shower cycle. By way of example we can take the above derived average shower length (based on Southern Water figures) of 5 minutes and 33 seconds and calculate the additional flow rate we’d obtain for 2 litres of pre-heated water at 120 degrees centigrade.

The deployable energy stored in the 2 litres of water is:

(120-20) * 4.186 * 2000 = 837200 Joules

Over 5 minutes and 33 seconds this gives 2514.11 Joules per second. The amount of water that can be heated from ambient to 36.8 degrees centigrade by 2514.11 Joules is:

2514.11 = weight of water * 4.186 * (36.8 – 20)

Weight of water = 35.75 grams

Thus the rate of flow would be increased from 90 grams per second to 125.75 grams per second for the entire 5 minutes 33 seconds. This is an increase in flow rate of about 40%.

It should be noted that the stored pre-heated water should be stored within an insulated container.

CLAIMS

A shower fully, or partially, heated by a pre-heated fluid that is held under some factor of atmospheric pressure making use of the fact that as a fluid is held under pressure its boiling point increases.
A shower as claimed in claim 1 where the fluid is water the shower can be made by either mixing the pre-heated water with the incoming cooler water or the incoming cooler water can be heated by way of a heat exchanger.
A shower as claimed in claim 1 where the pre-heated fluid is not water the heating of the incoming cooler water will always be made by the use of a heat exchanger.
A shower as claimed in claim 1 may have pre-heated fluid that may or may not be re-heated during the shower.
A shower as claimed in claim 1 using sufficient fluid held, above atmospheric pressure, just below its boiling point, heated by a standard electrical supply (typically rated at 13amps), can be combined with the cold water supply, at ambient temperature, to produce a shower.
A shower as claimed in claim 1 using sufficient fluid held, at or above atmospheric pressure, just below its boiling point, can be combined with water heated by a shower (typically supplied by a 32amp power source) to produce increased water flow, whilst maintaining a stable temperature, and the increase and duration of the increase can be selected by the shower user.
A shower as claimed in claim 1 using sufficient fluid held, at or above atmospheric pressure, just below its boiling point, can be combined with water heated by a shower (typically supplied by a 32amp power source) to produce increased temperature whilst maintaining a stable water flow, and the increase and duration of the increase can be selected by the shower user.
A shower as claimed in claim 1 using sufficient fluid held, at or above atmospheric pressure, just below its boiling point, can be combined with water heated by a shower (typically supplied by a 32amp power source) to produce both increased temperature and water flow, and the increase and duration of the increase can be selected by the shower user.

ABSTRACT

Pressure Shower

To be able to increase the performance of an electric shower, of any power rating, by the use of pre-heated stored fluid held under a factor of atmospheric pressure. Examples of implementation could include the ability to provide a shower which adequately functions off a 13amp mains electricity supply or to be able to operate a 32amp electric shower with the performance of what is commonly referred to as a power shower.