It’s well known a lot of heat is lost through windows.
With single glazing the Thermal Resistance, ‘R’ Value is 0.16.
Although they aren’t considered in energy calculations (see this link: Energy Rating) curtains can significantly decrease the heat loss from a window.
They also improve the feeling of comfort.
Insulation Value
With different materials its not possible to give a definitive value for the insulation value of curtains however there are some indicative values in this post.
An effective curtain can increase the ‘R’ value of the window to between 0.3 – 0.5.
Even with a double glazed window curtains will typically further reduce the heat loss. (‘R’ value increased from around 0.33 to around 0.6).
Effective Curtains
To be fully effective curtains must:
Provide a ‘seal’ around the window to stop air movement at:
Top – Pelmet
Bottom – Overlap window sill by at least 300mm, or down to the floor
Sides – Overlap edges of window by at least 300mm.
The ratings are calculated by a NatHERS (Nationwide Housing Energy Rating Scheme) computer simulation of an individual house design to estimate the thermal comfort.
The calculations are based on 69 different ‘Climate Zones” and allows comparison of different properties in the same climate zone.
The following table shows the Energy Load (heating,cooling, lighting and hot water) for various capital cities for each of the star rating band.
6 Star
7 Star
8 Star
9 Star
10 Star
Adelaide
27
19
13
6
1
Brisbane
12
10
7
5
3
Hobart
43
31
20
9
0
Melbourne
32
23
15
7
1
Perth
19
14
9
5
1
Sydney
11
8
6
4
2
The values are in kilo watt hours/m2/annum.
I haven’t shown less than 6 stars as that is the minimum for new houses.
As you can see if you go all the way to 10 stars the energy load will be virtually nil.
Example
If you are building a 200m2 house in Melbourne at the minimum 6 Star Rating your annual energy load will be:
200 x 32 = 6,400 kilo watt hours
By increasing the rating to 8 star the calculation becomes:
The suns position in the sky varies throughout the year and over each day.
The ideal situation is when the sun is hitting the panels closest to a perfectly perpendicular angle (90°).
So in Australia, what angle and orientation are best?……….. Well when mounting solar panels there are two elements of the alignment that affect the final efficiency of the panels.
Orientation – the compass direction the panel faces
Ideally in the southern Hemisphere solar panels should be facing as close to true North as possible to reduce the impact that the Winter seasons have on efficiency. Once the angle is above 30 degrees from North the efficiency really starts to drop away.
Tilt – the angle from the horizontal
The tilt is the angle that the panels are facing up into the sky. On a flat roof, the tilt is 0°, whereas if the panels were on a wall, it would be 90°.
The best tilt angle for more even efficiency throughout the year is generally the same angle as the degree of latitude of the site. Best for if your only power supply is solar.
Flatter tilt angles increase the power generated during summer, but reduce the winter power generation. If you have a system connected to the grid then you can go 15 degrees flatter than the degree of latitude without losing annual efficiency. (It can even help if your roof doesn’t face directly North)
Alignment Efficiency Table
The table below provides an indication of the approximate solar panel efficiency levels for Melbourne for various alignments.
Orientation
Tilt
15 degrees flatter
Angle of latitude
15 degrees steeper
North
100
100
94
30 from North
98
96
90
60 from North
93
89
82
90 from North
86
79
71
The following site will carry out calculations for sites around the world:
You may be out shopping for a new fridge to go in the new house
or
You may just want to check your existing fridge fits in the alcove in your new kitchen.
Whichever it is . . . . . Don’t forget to leave room around the fridge!
Ventilation
Both refrigerators and freezers work by extracting the heat from inside to a radiator coil on the rear of the unit.
If the air flowing past the coils is restricted the efficiency of the refrigerator will drop, and your power bills will go up.
I would recommend a space at least 25mm either side of the cabinet and 40-50mm behind and above the top of the unit.
Don’t then use these spaces to store trays, chopping boards, etc otherwise you are going to block that ventilation path.
I have heard of people installing an external vent behind a fridge mounted on an external wall. . . It seems like a good idea if you remember to shut the vent on hot days. (remember on a 30 + degree day the incoming air will be hotter than the air in the room)
Door Opening
To get drawers out of a Fridge or Freezer you normally have to open the door by much more than 90 degrees. (I have just checked mine and its about 135 degrees)
This means you may need more than the 25mm suggested above on the hinge side unless the front of the fridge projects forward of the alcove.
Built in Fridges
I’m not a big fan of built in fridges, but if you like them make sure that ventilation and door opening are fully considered before you buy.
As I have been travelling round I was remembering something I felt was very strange when I first got to Australia. . . . . . It was as soon as you went through the front door you were in the main living space of the house.
In the UK most houses have an enclosed porch like this photograph; or an internal space with a door to the inside (a vestibule)
These ‘Air Lock’ rooms can be important in helping keep heating and cooling bills down.
Advantages of ‘Air Lock’ Rooms
The advantages of Air Lock Rooms are:
Acts as a Buffer Zone slowing down the rate of heat trnsfer through the door and side panels;
Slows down the house Ventilation Rate by reducing drafts (air loss around a closed door);
Stops massive heat loss when a door is opened (as long as you treat it like a true air lock and always keep one door closed). . . .useful when you have people at the door you don’t want to invite in.
A useful security feature as wide windows allow you to check out callers that might be hiding out of the view of CCTV cameras.
Types of ‘Air Lock’ Rooms
As well as enclosed porches and Vestibules mentioned above other common ‘Air Lock’ rooms are:
Mud Room;
Laundry;
Enclosed veranda:
Sun Room/Conservatory.
If you are serious about saving energy perhaps you should think about ‘Air Locks’.
I spent a couple of hours last week looking around the Australian Solar Council ‘Solar 2015 Exhibition and Conference‘.
So here are a few things which may be of interest if you are planning a new house.
Hot Water from Photovoltaic (PV) Panels
This is a Rotex Hot Water Service that uses Photo Voltaic Power rather than circulating water as the heating mechanism.
All very interesting as I was only wondering whether this sort of thing would be possible in the Hot Water Post back in April this year.
The company who are planning to sell this later this year are called Energy Smart Water.
You may have heard about the Tesla Powerwall for storing power from your solar panels for night time use but they aren’t the only company with battery options.
Fronius Solar Battery
On the Left is Solar Battery from Fronius Australia .
The standard Size of the unit is 955 x 570 x 611mm
Capacities rnge from 4.5kWh (kilowatt hours) to 12.0kWh
If you want to use it with existing solar panels you will need to replace the Inverter as it requires a special Hybrid Inverter.
LG Solar Battery
LG’s Solar battery at 406 x 664 x 165mm is smaller than the Froniius Unit but only has a capacity of 6.4kWh.
It can however be supplemented by up to two expansion packs of 3.2 kWh capacity.
This increases the size to, a still relatively compact 966 x 664 x 165mm.
Again this unit requires a special hybrid inverter.
The local agent for the unit are ‘Solar Juice’.
Currently the companies that are promoting these products say they will be available later this year when full pricing will be available.
All these are interesting ideas but of course the real test will be when the prices are released.
Well as you might have guessed the term originates in Germany, and relates to a method of achieving more sustainable performance (and lower Energy Bills)
It’s a technique which doesn’t rely on good orientation, high thermal mass and natural cross flow ventilation to provide comfortable conditions with low energy use.
The house on the right, built in Castlemaine by Carbon-Lite, is said to be the first Passiv Haus built in Australia
Some of the key Passiv Haus characteristics are:
High Levels of Thermal Insulation
All the exterior envelope (walls and roof) of the house are very well-insulated with a maximum Heat Transfer Coefficient, U-value of 0.15 W/m²K (R=6.6)
All Wall openings, corners, connections and penetrations are designed, and constructed, with great care, so that thermal bridges can be minimised.
Highly Insulated Windows:
Typically triple glazed windows will be required to achieve appropriate insulation
Air Tightness of the Building:
Uncontrolled air changes from gaps must be smaller than 0.6 of the total house volume per hour which is much better than 1.0 of the total house volume per hour that would be more typical of a new house.
To achieve Passiv Haus certification involves a test where the house is pressurised using a temporary ‘Blower Door’.
Energy Recovery Ventilation:
Because the house will be quite airtight a mechanical ventilation is required to keep the air fresh and prevent condensation.
Passiv Haus systems have highly efficient energy recovery ventilation systems
In Winter around 75% of the energy from the exhaust air is used to warm the fresh air again by means of a heat exchanger.
In summer the exhaust air is used to cool the incoming air
The ventilation systems also incorporate pollen and dust filters.
Could you just heat the water by electricity generated by your Photo Voltaic (PV) solar cells?
I have carried out a desktop exercise to help you review the options.
Solar Water Heaters
There are now hundreds of thousands of solar hot water heaters installed around Australia so the technology is well understood.
One of the main reasons for their choice is they are fairly simple.
Also they are very efficient, as around 60% of the sunlight that falls on the panel is converted to usable heat.
This efficiency has meant that the panel size can be kept relatively small.
Direct Heating with PV Panels
Efficiency of Solar Photo Voltaic (PV) is much lower than solar hot water at around 20%.
To provide comparable direct heating using PV panels and an immersion type heater will need an area of panels larger compared with a solar hot water heater.
How Many Panels Will Be Needed
The equation for calculating the power to heat water is:
kW hours = litres x temperature rise in degrees centigrade / 853
Assuming the incoming water will be around 16ºC you are going to need to raise the temperature to around 60ºC
for 200 litres of water the equation becomes:
kw hours = 200 x 44 /853 = 10.3 kwhr.
1,000 watts of panel on average generates around 3.5 kw hours per day .
So to provide hot water by PV panels you will need around 3,000 watts, a considerable area, and expense.
Using A Heat Pump With PV Panels
One way of reducing the area of PV panels needed for water heating is to install a heat pump.
The most common hot water heat pump systems extract heat from the air.
Efficiency of heat pumps does vary between winter and summer but an overall Coefficient Of Performance (COP) is typically around 3.
That is for every 1 kW of electricity 3kW of heat are produced. (300% efficiency)
To get the best benefit from Grid Connected Solar Power you need to be up to date with the latest tariffs that apply to your installation.
These days the Feed In Tariff (FIT) is much less than a few years ago.
Power Tariffs
Here in Victoria the FIT for excess power put into the grid for new installations is $0.062/kwhr.
The above rate will also apply to existing installations that:
Are coming to the end of the initial scheme that had a higher FIT.
Have been eligible for a higher FIT but want to increase the number of panels.
This compares with my current tariff for power consumption of $0.248/kwhr. (I could get lower ‘Off Peak Power’ but it is a balance between paying more for ‘Peak’ and less for ‘Off Peak’)
Although these rates are specific to me the general relationship will be similar for most locations in Australia.
Change Your Usage Patterns
To maximise the benefit from the current tariffs you need to ‘Change Your Usage Patterns’ to maximise the use of the solar power when it is being generated.
To achieve this, during daylight hours, you should aim to:
Wash and dry clothes. (although drying clothes on the line is better than driers).
Cook meals and bake, for electric ovens, and cook tops. (or use a ‘Crock Pot’).
Run your swimming pool filter.
Recharge battery appliances.
When you are planning to change your usage patterns remember to stagger the operations times so you are less likely to exceed the output of the panels.
Although this does minimise power going to the grid. . . the real purpose is to minimise your power used when the panels aren’t generating and you are importing from the grid.
Consider Panel Orientation
If you are planning a new installation there are real benefits in installing a panel that will give maximum power generation when you would normally use the power.
For most of us that will mean considering a more Westerly Orientation, rather than the traditional north facing orientation.
This will means that you will be best placed to use the ‘Free’ Solar Power from, when you come home, until sunset.
If you find you use more power in the morning, then East facing panels would be of benefit.
Basically an inverter is a device which converts the electricity from your solar panels to a form that can be used by normal domestic appliances, and lights.
The electricity generated by the solar panels is Direct Current (DC) but the typical home runs on Alternating Current (AC)*.
*It is possible to run a home on DC electricity without an inverter but you will need to buy special appliances, such as those designed for caravan use. The wiring requirements are also quite different!
Types of Inverter Applications
There are three types of inverter applications which all require different types of inverters, which are:
Stand Alone Inverters
These are used for houses that are not connected to the local power grid. The solar panels charge a bank of batteries by Direct Current. When an appliance is switched on the inverter converts the DC electricity from the batteries into AC power.
This is a relatively simple form of inverter, and the system as a whole has the following characteristics:
No power bills.
Unaffected by power cuts.
Initially expensive due to the cost of a large bank of batteries.
You may need an auxiliary power supply such as a generator for long periods with little sunlight.
Grid Tie Inverters
The most common form of inverter these days. The solar panels feed Direct Current into the inverter which converts the electricity into AC power. The power is then used by any appliances that are on, with excess electricity being ‘pushed’ into the grid. (You will be credited for this electricity) If electricity demand greater than the solar panels can provide power is taken from the Grid.
Reduced power bills.
A power cut will result in complete loss of power.
Lowest cost solar power system.
Dual Inverters
Also called Battery Backup Inverters. The solar panels charge a bank of batteries by Direct Current with the batteries providing power to the house in a similar manner to the standalone system. When the batteries are fully charged any excess power is ‘pushed’ into the grid. (You will be credited for this electricity)
This is the most complex and expensive type of inverter, The system as a whole has the following characteristics:
Reduced power bills.
Unaffected by power cuts for several hours (depending on battery capacity).
Mid range cost. Although the inverter is expensive there are typically far fewer batteries than a stand alone system.
