Chapter 4 Hot water, Lighting and electrical devices

4.1 Basic Concepts

4.1.1 Electrical Potential

\[P = U\times I\]

Where:

\(P\) : Power (Watt)

\(U\): voltage (volts)

\(I\): current (Amperes)

4.1.2 Power Factor, Voltage and current phase relationship

4.1.2.1 Power triangle

Where:

\(S\): Apparent Power (measured in VA)

\(P\): Real Power (measured in Watt)

\(Q\): Reactive Power (measured in VAR)

4.1.2.2 The Powe factor is given by

\(cos\phi\)

\(Power \ Factor \ (cos\phi)=Real \ Power(W)\)

\(Apparent \ Power \ (VA)\) \(|S|^2=P^2+Q^2\)

\(|S|=\sqrt{P^2+Q^2}\)

\(cos\phi=PS\)

4.1.2.3 Voltage and current phase relationships

Electrical loads can be classified according to their nature as Resistive or Reactive (either can be Capacitive or Inductive and combination).

A purely resistive load gives a voltage and current waveform output similar to the figure on the right and a partially inductive load give a voltage and current waveform output similar to the figure on the left.

Notice the orange line (left figure) goes negative for a period of time, the positive bit is energy flowing to the load and the negative bit is energy flowing back from the load.

4.1.2.4 Resistive Load

cos\(\phi=0^\circ\) (purely resistive)

E.g.Incandescent light bulbs, kettles, irons, electric water heaters, electric cookers

Resistive loads consume electrical power in such a manner that the current wave remains in phase with the voltage wave. That means power factor for a resistive load is unity.

They use all the energy given to them. They are resistive loads which means their current draw is equal to the voltage divided by their resistance (Ohm’s Law).

4.1.3 Reactive Loads (Q)

However, some appliances take in a certain amount of energy, then release some energy back into the mains supply. These have inductive or capacitive components in addition to the resistive component.

The other thing to consider is that the voltage and current waveforms have been shifted apart. Imagine charging a fairly large capacitor with a resistor in series (so that it can’t charge instantly): To start with, the capacitor is discharged. The supply voltage rises and is higher than the voltage on the capacitor, so current flows into the capacitor (the positive direction on the graph), which causes the capacitor voltage to rise. The supply voltage falls. Now, the voltage across the charged capacitor is higher than the supply voltage. Current starts to flow back in the direction of the supply (the negative direction on the graph). This causes the current waveform to appear as if it is shifted, as depicted in the graph (this is referred to as phase shift).

4.1.3.1 Capacitive Load

\(S = P - jQc\)

\(cos\phi=-90^\circ\) (purely capacitive)

A capacitive load causes the current wave to lead the voltage wave. Thus, the power factor of a capacitive load is leading.

E.g.: capacitor banks, buried cables, capacitors used in various circuits such as motor starters etc. Inductive Load

\(S = P + jQi\)

\(cos\phi=90^\circ\) (purely inductive)

An inductive load causes the current wave to lag the voltage wave. Thus, the power factor of an inductive load is lagging.

E.g. transformers, motors, coils etc.

4.1.3.2 Power triangle in Inductive and Capacitive Circuits

Total Reactive Power (Q) is the difference between inductive (Qi) and capacitive (Qc) elements

\(Qi > Qc -> Inductive\)

\(Qc > Qi - > Capacitive\)

4.1.3.3 Example

Consider the following building:

City hall (Paços do Concelho), in Lisbon

This is the energy consumption of the city hall (Paços do Concelho), in Lisboa, on the 30th of October 2013

4.1.3.3.1 Lisbon City Hall (Paços do Concelho)

As you can observe it changes along the day.


So consider 3 different points, with different moments of the day:

Timedate Active Power (kW) Reactive Power (Capacitive Load) (kVAR) Reactive Power (Inductive Load (kVAR)
03:00 13 4 0
06:15 21 3 2
09:00 76 0 11

  1. Calculate P, Q and S

  2. Calculate the Power Factor (Pf ) at 6:15 A.M

4.2 Hot water modeling

Formulas:

Changing Product Temperature - Heating up the Product with Steam

The amount of heat required to raise the temperature of a substance can be expressed as:

\(\Delta U = m cp \Delta T\)

Where:

\(\Delta U\) = quantity (difference) of energy or heat (kJ)

\(m\) = mass of substance (kg)

\(cp\) = specific heat of substance (kJ/kg K)

\(\Delta T\) = temperature (difference) rise of substance

\(Cp\) 4.18 kJ/kg.K

4.3 Electrical Appliances

An important part of the energy consumption of these appliances is the hot water generation, which could and should be included in the hot water service. In any case, part of the cycles, like the centrifugation or drying are always electric. Then, there are some appliances related to cleaning that are also electrical, like vacuum cleaners, iron machines, clothes dryers. All these appliances are in general appliances that work directly with AC.They also have losses in the conversion, but it depends on the type of electric elements that they use in their circuits.

The use of these appliances can be classified in three categories:

the continuous operation (e.g.fridges), perate continuously, 24 hours 7 days a week without interruption

interruptible operation (e.g. water heaters) whose operation can be interrupted for some period without affecting the service

non-interruptible operation (e.g. dish washers) when switched on, they should conclude their operating cycle until the end.The service provided by an electric appliance is therefore defined by the activity requirement (which is related to the power), and the time period during which is required.

All these devices are in general electronic devices which means that they are devices that require low voltage Direct Current (up to 24 V) and they all include a power source to convert from AC to DC, which means that there is an efficiency loss in its use just due to the power conversion. We also have other types of appliances that are in general electric, though theoretically their service could be provided by other energy forms.

4.3.0.1 REFIT Electrical Load Measurements Dataset (example)

4.3.0.1.1 Household Information
House Occupancy Construction Year Appliances Owned Type Size
1 2 1975-1980 35 Detached 4 bed
4.3.0.1.2 Appliances
Item Brand Model
1 Fridge Hotpoint RLA50P
2 Freezer(1) Beko CF393APW
3 Freezer(2) Unknown Unknown
4 Washer Dryer Creda T522VW
5 Washing Machine Beko WMC6140
6 Dishwasher Bosch Unknown
7 Computer Lenovo H520s
8 Television Site Toshiba 32BL502b
9 Electric Heater GLEN 2172
Metadata summary
Design Type(s) observation design; time series design
Measurement Type(s) whole house energy consumption; appliance-by-appliance energy consumption
Technology Type(s) wireless transmitter; plug-in individual appliance monitors
Factor Type(s)
Sample Characteristic(s) United Kingdom ; building
4.3.0.1.3 Timestamp

2013-10-09 14:47:17 - 2013-10-10 14:47:17 UTC

4.3.0.2 Fridges and freezers for food conservation

4.3.0.3 Fridges and freezers for food conservation

Though the first refrigerators in the XIX century as we know today were not electrical, most of them are today technology based on electrical appliances. Regarding food preparation, electrical appliances are being used more and more, especially in developed countries. Apart from the coffee machines and tea electric kettles, we have an increasing use of microwaves, electric ovens and stoves.

4.3.0.3.1 Food Conservation

In the case of food conservation, it is important the volume required to store food and the temperature at which will be stored (for example: 5 ºC for a fridge, -18ºC for a freezer). In this case, the time period of use is 24 hours a day. The energy consumption is related to the volume (more volume requires more powerful compressors) and with temperature (lower temperatures require in general more power).

4.3.0.4 Clothes washers and dishwashers

4.3.0.4.1 Clothes washer

Clothes washers, the activity level is defined not only by the water temperature that is going to be used in the cycle (for example 40 ºC for colored clothes, 60 or 90 ºC for white clothes) but also the volume of clothes that is washed (7 or 8 kgs).

In the particular case of clothes washer, although the power of the appliance is always the same (and it is defined by the electrical resistance that is used to heat the water), the amount of energy varies depending on the type of cycle (mostly because of the temperature, but also because of the duration of the cycle). So, in these cases it is more common to have an energy consumption per cycle and the time period is in general the number of cycles per unit of time that the service is done (for example 4 cycles per week or one cycle every two days).

4.3.0.5 House keeping

  • Dehumidifier = 785 W
  • Clothes iron = 1000–1800 W
  • Vacuum cleaner = 1000–1440 W

4.3.0.6 Entertainment

  • Radio (stereo) = 70–400 W

  • Televisions(color)

  • 19" = 65–110 W

  • 27" = 113 W

  • 36" = 133 W

  • 53" - 61" Projection = 170 W

  • Flat screen = 120 W

  • VCR/DVD = 17–21 / 20–25 W

4.3.0.7 Working

There are many energy services that can only be provided by electrical appliances. Perhaps the most important example is the computation service, which is defined here as a service that includes gathering, storing and processing data to generate and display information. Today, all departments in all organizations in all economic sectors resort to computers and computational tools to develop most of their activities.

Computers and monitors are eventually today the most used appliances in offices.

A closely related service is the communication services, as most of the communications today between organizations and people is based on email and internet, which requires the use of routers - a device responsible to exchange data packages between computer networks.However, even traditional communication devices like telephones are today devices that require electricity. We also have general office equipment like printers, photocopy machines, scanners and then specific appliances depending on the activity that is performed, like for example the cameras and displays in this studio. We also have entertainment appliances like TV and consoles, radios and music-players, DV’s and others.

4.3.0.7.1 Personal computer

  • CPU

  • awake 120 W

  • asleep = 30 W

  • Monitor

  • awake 150 W
  • asleep = 30 W

  • Laptop = 50 W

4.3.0.7.2 Printers

  • Inkjet

  • Laser

4.3.0.7.3 Scanner

Copy

4.3.0.8 Communication

4.3.0.8.1 Router
4.3.0.8.2 DataShow

Computing power is usually measured in FLOPS (Floating-points operations per second). The time period can be for example a working day (8 hours or 24 hours).

We can see that the power consumed by a processor is related to the computational power measured in FLOPS. The communication service is measured in the number of bits that can be exchanged per second (MBits). We can see that different communication technologies have different service levels and that the power consumption of the devices is more related to the type of technology than the activity itself: for example wireless routers might consume less than Ethernet routers, which have the same communication capacity.

4.3.0.9 Others

  • Coffee maker = 900–1200 W

  • Kettle=1500-2000 W

  • Hair dryer = 1200–1875

  • Toaster = 800–1400

  • Toaster oven = 1225

  • Water pump (deep well) = 250–1100

4.4 Lighting Concepts

The lighting service is fundamental to develop productive activities (like reading, writing,cooking, sewing) whenever the natural light is not sufficient because it is evening or when these activities are developed in dark indoor spaces.

Lighting is also used to make an environment more comfortable, where comfortable might mean that is looks safer or cleaner.The most important example is the public lighting networks developed in the XIX and early XX century that contributed to reduce significantly the crime rates in large cities.

But, what is light?

Light or visible light is the part of the electromagnetic spectrum radiation that is captured by the human eye. The frequency band lays between 430 and 770 THz (or is the radiation with the wavelength between 390 to 700 nm) and is the radiation between the infrared and the ultraviolet radiation.It is also the frequency band where the radiation emitted by the sun, which covers basically all the electromagnetic spectrum, is strongest.Like any object that behaves like a wave, light is an electromagnetic wave that can be reflected, refracted or transmitted and absorbed.

Reflection means that when the light reaches a surface it can change the direction, in general with the same angle as the incident angle of the radiation. That is what happens in mirrors and metal surfaces.

Refraction (or transmission) means that the light when reaches a surface it is able to enter the surface, though the velocity and direction might change.

Finally, light can also be absorbed, which means that the wave energy is absorbed by the electrons that compose the surface material and changes the surface properties (for example it may increase the temperature).

This is the case, in general, of dark opaque surfaces, like wood.

As waves, it is also important to notice that the superposition principle apply for light waves emitted from different sources on the same point, which means that waves can be summed so the effect can be amplified or canceled.

Natural light is the light emitted by the sun.However, we can use the other sources of light, which we call artificial light as opposed to natural light of sun.

The main difference is the bandwidth of the emitted radiation and its power density. Let’s look to the power spectrum of two of the most common artificial light technologies supplied by electricity: incandescent lamps and fluorescent lamps. The incandescent lamps power spectrum has more power density around 600nm, which is the frequency band around the dark yellow-orange colors, so it means that our eyes will see this lamp with that particular color.

Now, the frequency band shows that the lamp also emits at higher frequencies which correspond to the infrared spectrum, which means that, in general, this type of lamp is also a heat generator. So these lamps not only generate visible light but they also generate heat, which for the purpose of providing lighting service is useless.

The fluorescent lamps power spectrum is different from the incandescent lamps. Usually the frequency band has a wider bandwidth and is less smooth spectrum. This means that the lamp emits radiation in many wavelengths, from lower frequencies (like blue), brighter yellow or even green frequencies, and also higher frequencies (like orange and red). So in general, this lamp is perceived by our eyes as white, because it is a mix of different colors.

But how do we measure light, or the quantity of light or quality of light?

4.4.1 Lighting Concepts

For that we will introduce some concepts: the luminous flux, the luminous intensity and the illuminance.

Let’s assume that we have a system that generates light, meaning that emits a radiation spectrum with frequencies within the visible light: an incandescent or fluorescent light, a candle, or even the sun. This body generates light in all directions and this light is captured by some surface at a certain distance. The luminous flux is the quantity of light that is emitted by this luminous source in all directions.

Luminous Flux (\(\Phi\ : lm\setminus m^2\))

It is basically a measure of the perceived power of the light captured by the human eye. The measurement unit is lumens.As the body radiates in all directions, when we look to a particular area around the source (to a particular solid angle around the source), we can measure the luminous flux per area of the solid angle.

This is called the luminous intensity and its measured in candelas (where one candela is one lm per sr (steradian or square radian), the SI unit of solid angles).

When the light reaches a certain surface, we can measure the luminous flux per unit of surface area. This is called the illuminance and it is measured in lux (lm per square meter, the unit of area). The illuminance is an important measure because it is relatively easy to measure and from which it is easy to define quality requirements for lighting.

The equipment that is used to measure illuminance is called the light meter and provides a quick, cheap and relatively accurate measurement of the light available in a surface to develop the productive activities like reading or writing. In general, we have the characteristics of light sources like the luminous flux of a certain lamp.

How do we measure the illuminance available on a certain surface?

For that we need to know the luminous flux, the distance to the light source and the incidence angle between the light source and the surface. So the illuminance E at a certain point, is given by the product between the luminous flux times the cos of the angle of incidence divided by the distance.So the greater the distance between the light source and the surface, the smaller the illuminance is because the flux is less dense.

Again, remember that if we have two light sources we can add the illuminance effect of two light sources (for example natural and artificial light sources).

4.4.2 Lighting Conditions

4.4.2.1 Lighting

Light design (natural + artificial)

  • Light impacts directly on
  • Visual Comfort
  • Productivity
  • Energy Consumption
  • These objectives are sometimes conflicting

4.4.2.2 Measuring “Light”

  • Luminous Flux – quantity of light emitted by a luminous source in all possible directions (lm)
  • Luminous intensity – Luminous flux per unit of solid angle (cd)
  • Luminous Efficacy – Ration between the luminous flux and the power of the source (lm/W)
  • Illuminance – ration of luminous flux by the area of incidence (lux=lm/m2)
  • Luminance – ration between luminous intensity emitted in a given direction and the apparent area of the luminous

4.4.2.3 Illuminance

  • Type of space
  • Activity

4.4.2.4 Natural lighting strategies

4.4.2.4.1 Artificial light
  • Incandescence
  • Simples
  • Reflector

  • Halogen

  • Fluorescent
  • Tubular

  • Compact

  • LED

4.4.3 Visual comfort

Visual comfort is a subjective impression related to the quantity, distribution and quality of light.It depends on the age, the gender, the eye sensitivity, which means that for the same conditions of light, different people will feel differently.

One of the most important parameters that define visual comfort is having the right level of illuminance required to develop a certain task, as having too much light or not enough light to develop a certain activity impacts on the productivity and the accuracy of the task.

So what are the required illuminance levels to perform a certain activity?

In general, the greater the precision and concentration required to develop a task,the greater is the required illuminance.

Sometimes the illuminance levels are not described by activity but by the type of space, which is in generally strongly correlated with the activity. For example, walking in corridors or going to the toilet requires a certain amount of light that is enough to recognize the environment shapes and the objects even if it is not enough to detect small details.

In general, 100 Lux is considered the minimum illuminance level for these type of activities.

Eating in a cafeteria or refectory requires more illuminance (200 Lux),for example to distinguish different types of food, detecting if they are clean or fresh or well cooked, or to handle food, like detecting bones or fishbones. If we are developing activities that require reading and writing, like office places or class rooms or libraries, 300 Lux is enough to develop these activities. However, if we are working with a computer, our illuminance at the desk should be around 500 Lux.

And the greater precision the task requires, like handling samples in chemical labs, or welding components in electronic labs, the higher the illuminance should be (e.g. between 750 and 1500 Lux).

However, and this has for sure happened to you, even if the illuminance level is correct for the task that is being performed, people react differently to the light colors.

The light processed by our eyes participates in the regulation of our internal clock watch, which means that our body functions are executed and processed by the human brain depending on the light conditions. As an example, the light helps to control biological cycles like regulating body temperature, sleep and even our mood.

But, have you ever thought why light in cozy restaurants, or in our living room and bedrooms, is, in general, yellow?

The reason is that for most people, yellow colors creates a sensation of relaxation (just like the sun colors at the sunset).

In office spaces, classrooms or kitchens the lights should be always white, as in general, white colors create in us the sense of cleaning spaces and active spaces (just think about the white light color at midday).

Thus, the light color (and consequently the light technology) is an important variable for the lighting service. There is another important concept which is the color temperature of a light source.

As described by the Wien Law, in any body (black body) the frequency of the radiation with highest energy density depends on the temperature of the body (measured in Kelvin).

4.4.4 Wien’s displacement law

Wien’s displacement law shows how the spectrum of black-body radiation at any temperature is related to the spectrum at any other temperature. If we know the shape of the spectrum at one temperature, we can calculate the shape at any other temperature. Spectral intensity can be expressed as a function of wavelength or of frequency.

A consequence of Wien’s displacement law is that the wavelength at which the intensity per unit wavelength of the radiation produced by a black body is at a maximum, \(\lambda_\max\), is a function only of the temperature:

\[\lambda_{\max}={\frac{b}{T}}\]

Where:

\(T\) is the absolute temperature in kelvins. \(b\) is a constant of proportionality called Wien’s displacement constant, equal to 2.8977729(17)×10-3 m⋅K

Planck’s law was also stated above as a function of frequency. The intensity maximum for this is given by

\[\upsilon_{\max} = T \times 58.8 GHz/K\]

Often the lamps in supermarkets indicate the temperature of the lamp.Thus, a lamp is a system that radiates visible light at a certain temperature, depending on the color of the light that is emitting.In this case, the higher temperatures correspond to the bodies that emit yellow light, and the lower temperatures correspond to the bodies that emit white and blue lights.

This is somehow the opposite of the common sense feeling that the cold colors are the white and blues and the warm colors are the yellow colors (for the reasons explained in the previous slides).

4.4.5 Glare

Glare is the effect caused by the difficulty to see in the presence of bright light, such as direct sunlight reflected in computer screens or even the pages of a book, or the artificial light from cars headlamps, camera flashes or a light fixture directly above on our desk. This means that too much incident light may also be disturbing for the human eye.So, at the end, providing the correct lighting service on indoor requires a balance between natural and artificial light but also between direct and indirect light.

The elements of control of light are therefore not only the lamps (or light fixtures) and its location relatively to the places where the activities have been developed, but also the windows location and the shading systems (like blinds, curtains and others). The control of all these variables may cause significant impacts on other dimensions. If, on one hand, the lighting control has a direct impact on the visual comfort, it may also impact on the thermal comfort.

A very simple example is the fact that in the summer, the use of natural light, though good for visual comfort, may be bad for the thermal comfort, as the people near the window will feel much hotter than the rest.

Then, the option between using direct light or artificial light, or increasing the thermal gains to decrease artificial lights may have a significant impact also on the energy consumption.For example, on the use of artificial light vs natural light and on the need to cool more a space that uses more direct sunlight.

This relation between visual and thermal comfort is therefore very important for the management of lighting and space heating and cooling services, but also for the design of buildings. For example, buildings with high glazed areas have often a lighter appearance, which is important from the esthetic point of view.

It is also good for daylight availability, though it may impact on the visual comfort due to glare, and it is also good in winter to increase the solar gains. However, in summer, it may increase significantly the cooling needs.

4.4.6 Illuminance from a Light Source

\[E = \frac{lcos\Phi }{d^2}\]

Where: \(E\) : illuminance from a certain place (lux)

\(d\) : distance to the light source

\(\Phi\) : Angle from the light source

\(I\): light source luminous intensity (lm)

4.5 Lighting Service (L)

The first step is to determine the activity that is going to be performed in a certain space, or identify the type of space that needs to be illuminated: if it is a space where people walk, or eat or develop some working activity, and from those, which level of precision of the task will be required.

Then, we need to characterize the area that needs to be illuminated. This includes not only the actual size of the area where the activities are being developed, but also the number of tables or workstations or lab benches that will be distributed. Another important aspect is during how much time the space needs to be illuminated. This is in general related to the occupancy of the space by the users.

In fact, how many hours are they supposed to walk through this area, how many hours will take them to eat, or how many hours they will work in this space.

In conclusion, the lighting service consists basically in describing for how long a certain activity will be developed in a certain area.So, conceptually, it is the illuminance level required in a certain area during a certain period, or the luminous flux required during a certain time interval.And remember that at this point,it does not really matter if the lighting services is supplied by natural or artificial light.

Amount of time that the activity takes place

\[L = E\times A\times \Delta T(lm. s)\]

Where:

\(E\) : Required level of illuminance in a certain place (lux)

\(A\) : Area which requires a certain level of illuminance (\(m^2\))

\(\Delta\) : time period

4.5.1 Inverse Square Law

(The intensity of illumination produced by a point source varies inversely as square of the distance from the source.)

\[E = \frac{I}{d^2}\]

Where:

\(I\): intensity of illumination

\(d\): distance from the source

4.5.2 Cosine Law (Lambert’s Law)

\[E_H = \frac{I}{d^2}\cos\Theta\]

\(I\): intensity of illumination

\(d\): distance from the source

\(\Theta\): angle from the light source

4.5.3 Cosine Cubed Law

\[E_H = \frac{I}{d^2}\cos^3\Theta\]

4.5.4 Useful Lumen Output (ULO)

\[ULO = (n\times N\times F)\times(UF)\] Where:

\(n\): lamp number per fixture

\(N\): total fixture number

\(F\): Individual Lamp Lumem output

\(UF\):utilisation factor

4.5.5 Illumination Average Area

(rate of the portion of Lumen Output with influence in the lighting of an area)

\[E = (n\times N\times F \times UF \times LLF)/A\]

Where:

\(E\): Illuminance Average (in lux)

\(n\): lamp number per fixture

\(N\): total fixture number

\(F\): Individual Lamp Lumem output

\(UF\):utilisation factor

\(A\):Area

\(LLF\): Light Loss Factor

4.5.6 Efficacy Index

\[P(W)/100 (lux)/m^2\]

(it shoud be \(<5\))