163 Lo3.2

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• Solar

–Still requires booster element

–8-10 year pay back period

–May require extra roof support.

–Does the roof face the required direction?

–Is the roof corrugated asbestos / fibro?

Other water heaters

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Other water heaters

91 Revision01• Heat pump HWS

Other water heaters: heat pump HWS

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• Three possible: Continuous Tariff 11

•Available all the time

•Cost: Reduces with increased usage

–Cost for initial kWh’s = 18c

–Usually it averages out to about 12c per kWh

•All light and power is on this tariff

•Many HWS are on this tariff also

Tariffs

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–Controlled load Tariff 33

•Available a minimum of 18 hours per day

•Cost per kWh approx. 7c

•May require a bigger HWS as it is only on for 18 hrs/day

Tariffs

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–Off peak Tariff 31

•Available a minimum of 8 hours per day

•Cost per kWh approx. 5c

•Requires bigger HWS as it is only on for 8 hours per day

•Requires bigger element to heat this larger amount of water in the shorter time.

Tariffs

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• Types:

–High Temperature radiators

–Low temperature panels and convection units

–Thermal storage systems

–Heat pumps (reverse cycle air conditioners)

Space heating

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Space heating

• Types:

–High Temperature radiators

•Fixed radiators

–They radiate about 50% of the heat produced.

•Strip heaters

• IR lamps

–Require no warm up time.

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Space heating

• Types:

–Low temperature panels and convection units

•Under-carpet / under concrete heaters (MIMS in concrete slab)

–Can be operated using cheaper power at night

•Blower heaters

•Oil filled floor heaters

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• Types:

–Thermal storage systems

•Heat is stored in an insulated heat storage core, and extracted by a fan which is controlled by a thermostat.

•They draw electrical energy on a controlled load tariff.

•They can use water, or solid bricks

•Water is good because it requires more heat per kilogram to change its temperature than most other materials.

–It is also used in A/C systems on high rise buildings to cool each floor from an A/C plant on one floor.

•They require a ducted air system

Space heating

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Space heating• Types:

–Heat Pumps

•Same as reverse cycle air conditioners.

•More efficient than radiators.

–ie. More heat output than power taken from supply.

•They dissipate any power taken from supply as heat in the room AND pump heat from outside the house into the house.

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• Stoves (ranges):

–Four types of cooktops:

•Solid element

•Coiled element

• “Ceramic” cooktop

• Induction cooktop

Cooking

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Cooking

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•Cooktops:

•Solid

–Subject to corrosion on the surface. Looks bad!

–Slow to heat and cool.

Cooking

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Cooking

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• Cooktops:

•Coiled

–Stoves with these are, in general, cheap (why they are chosen)

–Good general purpose element

–Some have poor contacts that can fail

–More difficult to keep clean

Cooking

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Cooking

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• Cooktops:

•“Ceramic”

–They look good (why they are chosen)

–Quick heat

–Easy to clean

–Most expensive of the commonly used elements

Cooking

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Induction Cooktops

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• Cooktops:

•Induction

–Three times the price of a normal electric cooktop

–Heats a saucepan 3-4 times quicker than gas

–Cooktop does not get hot, so easier to clean

–Can only use steel (magnetic) pans

–With no saucepan on, the “element” will not work or get hot

Cooking

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• How induction cooking works

–When the cooker is switched on, an alternating current with a frequency of between 25,000 and 40,000 Hz flows through the induction coil underneath the hob, generating a rapidly alternating magnetic field. When a pan with a magnetic base is placed on this alternating field, the strong eddy currents generated in the base of the pan will cause it to heat up almost instantly.

Induction cooking

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Stove wiring: single phase

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Stove wiring: two phase

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Wiring: integral oven and cooktop range/stove

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Wiring: two circuitsseparate wall oven and cooktop (hob)

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Wiring: one circuitseparate wall oven and cooktop (hob)

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Cable current ratingDomestic: use 2/3 full load rating of stoveCommercial/industrial: use full load rating

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Microwave ovens

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• Microwave ovens bombard food with electromagnetic radiation at 2.45GHz

Microwave ovens

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• Microwave ovens bombard food with electromagnetic radiation at 2.45GHz

• Water absorbs the energy. The molecules vibrate and get hot.

Microwave ovens

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• Microwave ovens bombard food with electromagnetic radiation at 2.45GHz

• Water absorbs the energy. The molecules vibrate and get hot.

• The oven will dissipate the same energy in the cavity no-matter what. (eg. 800W)

Microwave ovens

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• Microwave ovens bombard food with electromagnetic radiation at 2.45GHz

• Water absorbs the energy. The molecules vibrate and get hot.

• The oven will dissipate the same energy in the cavity no-matter what. (eg. 800W)

• Small quantities will cook faster. Large quantities cook slower.

Microwave ovens

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• Microwave ovens bombard food with electromagnetic radiation at 2.45GHz

• Water absorbs the energy. The molecules vibrate and get hot.

• The oven will dissipate the same energy in the cavity no-matter what. (eg. 800W)

• Small quantities will cook faster. Large quantities cook slower.

• Metal reflects the microwaves

Microwave ovens

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• Microwave ovens bombard food with electromagnetic radiation at 2.45GHz

• Water absorbs the energy. The molecules vibrate and get hot.

• The oven will dissipate the same energy in the cavity no-matter what. (eg. 800W)

• Small quantities will cook faster. Large quantities cook slower.

• Metal reflects the microwaves

• If a microwave oven is left empty, the microwaves will reflect back into the magnetron and heat it up. This destroys the magnetron.

Microwave ovens

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• Key components:

–Magnetron

–HV Transformer

–Diode

–Capacitor

• The rest is all the trimmings

Microwave ovens

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Microwave ovens

• Faults:

–Magnetron gets “tired”.

•Test with water and calculate power dissipated.

–Capacitor / diode dies.

•Test with meter.

–Magnetron dies.

•Buy another microwave oven.

–Fuse blows.

–If not working…

•Check fuse, diode, capacitor, in that order.

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• Electrical heating in industry and manufacturing is widespread because:

–It is clean

–Lower risks

–More precise control

–More compact than other forms of heating

–Automation is relatively easy

–Higher temperatures are easily obtainable

Process heating

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Process heating

• Electrical heating in industry and manufacturing uses: