How
Much Does Your Hot Water Cost?
How
much does it actually cost to make hot water? An often asked question.
Firstly it depends greatly on what system is used and the price
of the fuel to run it! To answer this question properly, let's look
at it in more detail
The
energy required to heat water is the same, regardless of what method
is chosen. This is because the laws of physics dictate the energy
requirement, not the type or brand of product. Every liquid has
a "Specific Heat Capacity" value. In the case of water
that value is 4.187kJ / kg K.
This
means that 4.187 Kilojoules of heat energy is required to raise
the temperature of one kg mass (one litre) of water by one degree
C at standard temperature and pressure.
The
ability of any particular system to deliver this heat energy is
governed by its efficiency. If a system requires twice as much energy
to what can be extracted (in the form of hot water equivalent) then
the system has an efficiency of only 50%.
Some
common forms of water heating are:-
- Electricity
- Gas
(Natural or LPG)
- Heat
Pump
- Solar
- Combination
of some of the above
The
efficiency of systems within these groups can be generalised as
follows:-
| System |
Heater
Type |
Efficiency |
| Electric |
Storage |
70%
- 80% |
| Electric |
Instantaneous |
99% |
| Gas |
Storage |
49%
- 66% |
| Gas |
Continuous |
79% |
| Solar |
Storage
with Elec Boost |
75%
Elec Eff.
Ave |
Total
Sys. 249% |
| Solar |
Storage
with Gas Boost |
60%
Gas Eff.
Ave |
Total
Sys. 200% |
| Quantum |
Heat
Pump
Air Sourced |
Day
325% |
Ave
309% |
| Night
289% |
* The above figures are based on average Sydney conditions.
From the above
figures it will be evident that no system can exceed 100% efficiency
unless it can get some of its energy input from a free source that
does not cost any resource to produce.
In the case
of a solar flat plate heater, that source is the sun (direct or
diffuse radiation).
In
the case of a Quantum Compact Heat
Pump, that source is the heat energy in the environment
(sun, wind, rain & air).
In
the case of a Quantum Air Sourced
Heat Pump, that source is the heat energy in the
air.
The formula
to calculate the energy required to produce hot water is:-

There are 3.6
MJ in a kWh
The cost to
produce this energy requirement is arrived at by multiplying the
MJ or kWh by the purchase price for the fuel.
e.g.
$0.0676
/ kWh for off peak 2 electricity
$0.0127 / MJ for natural gas (small
volume user)
The
fuel costs per unit of energy are listed in the table below. These
are average for the Sydney / Newcastle region of Australia (June
2000). Although fuel prices may have changed since time of writing
or other regions may have different costs per kWh, the ratios are
still the same.
| Fuel
Tariffs |
| Fuel |
Tariff
(Example only) |
Electric Off Peak 1 |
$0.0372
/ kWh |
Electric Off Peak 2 |
$0.0676
/ kWh |
Electric Domestic |
$0.1025
/ kWh |
Gas (Large Volume User) |
$0.00962
/ MJ |
Gas (Small Volume User) |
$0.01270
/ MJ |
The
following table shows the cost to produce 1000 litres of hot water
at 45°C temperature rise, using the tariffs shown above for
the various water heating methods previously mentioned.
| Cost
Per 1000 Litres Of Hot Water |
| System |
Cost |
| Electric Storage Off Peak 1 |
$2.78 |
| Electric Storage Off Peak 2 |
$4.72 |
| Electric Storage Domestic Full Rate |
$6.70 |
| Electric Instantaneous Domestic Full Rate |
$5.42 |
| Gas Storage Standard Efficiency |
$3.70 |
| Gas Storage High Efficiency |
$2.75 |
| Gas Continuous High Efficiency |
$2.29 |
| Solar Storage With Electric Boost Off Peak 2 |
$1.42 |
| Solar Storage With Electric Boost Full Domestic
Rate |
$2.15 |
| Solar Storage With Gas Boost |
$1.20 |
| Quantum Heat Pump Air Sourced Off Peak 2 |
$1.14 |
While
these tarriffs may change with time, the relative costs should remain
similar. You may like to substitute the current costs in your area
to produce exact figures.
Please
check your local electricity Authority for applicable tarrifs in
your area. Canberra residents should contact ACTEW.
As
can be seen from this information, the Quantum
Heat Pump Hot Water System provides the lowest production
cost per 1000 litres of hot water. Why not contact Enviro Friendly World today, to see how much a Quantum Heat Pump
Hot Water System can save you?
Call
Enviro-Friendly today on (02) 6282 6266, and find out how a Quantum
solar hot water system can help you
"Save water, save energy, save
money, and save the environment."
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enviro-friendly tips and news, be sure to
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2002-2012 All
information provided in good faith- E&OE
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