Room Height

Rooms with higher ceilings always seem lighter and more spacious.

They can feel cooler in summer as the heat rises above your head, not so good in winter though!

They are better for fitting ceiling fans, probably the cheapest form of mechanical cooling. (see this link:  Ceiling Fans)

There is more choice of light fittings for tall rooms.

Most builders will normally provide a 2.4m ceiling height as standard.  However there are a lot of people who are willing to pay extra for a 2.55m, 2.7m, or even 3m ceilings.

So what are the issues?

  • According to the Building Code of Australia (BCA) there are certain minimum height regulations.
  • For most Habitable Rooms (for definition see this link:  Habitable Room) – The minimum height is 2.4m
  • For the kitchen (which is also a habitable room) 2.1m is the minimum allowed. Considering how much time we spend in the kitchen I think it’s strange that this should be considered different to other habitable room.
  • For Non-Habitable Room – For example bathroom, laundry, hallway, garage, cellar, storeroom then the minimum height is 2.1m.
  • You do get some dispensation for attics where you are allowed to have a bedroom with a sloping roof as long as 2/3rds of the floor area has a ceiling height of 2.2m. However you are not allowed to include in any floor area calculation any area with a ceiling height of 1.5m.
  • It can add significantly to your budget when you are Choosing a House or going through the Selection / Pre-Start.  For every 300mm that you want to increase the ceiling height for a typical house you can expect to pay in the order of $8,000-$10,000 in 2020 prices. That covers the cost of extra courses of brickwork additional frame cost, and dry lining.
  • It can affect the Outside appearance of the house. (See this link: Outside Appearance for more information)
  • Although you can fit a ceiling fan in a room with a ceiling height of 2.4m the fan blades will then be at a height of 2.1m, so you will need to be careful about waving your arms in the air! See the following link for more information: Ceiling Fans

Some builders quote ceiling heights in brick courses so the post on Brick Dimensions explains how to compare brick courses with ceiling height

 

See Guide to Choosing a House . . . for help picking your new house.

Or the ‘Selection / Pre-Start Guide’ for assistance with all the details

 

Ceiling Fans

If you have tall rooms a ceiling fan can make a real difference to your comfort without large bills.

Summer

While a ceiling fan does not lower the temperature it will make the room feel cooler by:

  • The breeze improving the ability of your body to lose heat by perspiration.
  • It mixes the cooler air near the floor with the warmer air near your face.

The combined effect is that you feel several degrees cooler.

So you may not have to run the air conditioning as much.

Most ceiling fans use less than 100 watts, which equates to less than 3 cent per hour to run.

Winter

Ceiling Fans can also help lower heating costs in winter.

You can run the ceiling fan in the reverse mode.

This stops hot air staying in the top of the room by pushing warm air up against the ceiling and then down the walls gently re-circulating warm air through the room.

Fan Selection

It’s important to consider the size of the room when selecting a ceiling fan.

The larger the room size the larger the blade diameter and the more powerful the fan motor will need to be to generate enough cooling breeze.

Also a small fan in a large room can make a space look unbalanced whereas a large fan can look overpowering in a small room.

Room Area

Fan Diameter

Up to 7m2

92cm (36inches)

7m2 – 13m2

92cm – 107cm(36 – 42inches)

13m2 – 20m2

122cm – 127cm(42 – 44 inches)

20m2 – 36m2

127cm – 132cm(44 – 46inches)

Installation

Any ceiling fan should be at least 2.1 metres from the floor to the blades of the fan and at least 300mm from the ceiling.

This is a minimum and if you have some basketballers, or ruckmen in the family it may need to be higher.

If you are planning on ceiling fans for a new house it is well worth making the rooms higher.

If you have got cathedral ceilings you can get a ball type fitting to allow them to be fixed to the sloping ceiling.

You can also get extension rods to lower the fan if they are too high to give an effective breeze.

 

For similar posts see Electrical

 

Cooling Options – Evaporative Cooling

A common standard builder’s cooling option is evaporative cooling.

This is probably because they are relatively cheap to install.

They also have fairly low power consumption as you are basically only running a fan.

So whats the down side?

  • Evaporative systems work best in areas of low humidity so they will be less effective in coastal areas where most of us Australians live.
  • They can only cool up to the ‘wet bulb’ temperature. (Check with the Bureau of Meteorology to find out what this may be, it might be OK for you)
  • To be effective you really need a door or window open in each room that you want to cool. Not too good if security is a concern, or you want to come home to a cool house.
  • A central unit will use around 25L per day which might be a significant consideration if you are on tank water. You can however shut the water off and rely on the breeze alone on some days.
  • There are some bush fire risks in having a large plastic structure on the roof. (DO NOT RUN AN EVAPORATIVE COOLER IF THERE IS A BUSH FIRE – It will suck flying cinders to the unit increasing the risk to your home)

Personally I am not a big fan of these units, because of the humidity they add I always feel a bit clammy. (In the USA they call Evaporative Coolers ‘Swamp Coolers’ for good reason!

If you have

  • Good House Orientation
  • A well Insulated house
  • Solar cells on the roof (which generate lots of power on hot sunny days)

The power use of a refrigerated system should be largely offset.

 

 

For similar posts see Selection

 

More on the details for your new home including 24 pages of Check Lists in the ‘Selection/Pre-Start Guide’

 

Multi Head Split System Air Conditioners May Not Be Best

Reverse cycle split system air conditioners are a popular choice for cooling.

They are also one of the cheapest heating systems to run.

Single Head Split System

These are the most common units, that you will see in most big box electrical stores, consist of a matched outdoor unit and an indoor unit.

Fine if you want the cooling in one room, but it can look a bit messy with lot’s of outdoor units if you have got several rooms to cool

There is however an alternative

Multi Head Split System

Multi Split systems consist of one outdoor unit running multiple indoor units.

In some cases up to 8 indoor units to be run off a single outdoor unit.

The indoor units don’t have to be all the same KW capacity so they can be matched to the room size

The outdoor unit can also be a little smaller than the sum of the indoor units

For instance if you had a 3 bedroom house you may have 2 x 3.0kw indoor units in family rooms and 3 x  2.0kw units in the bedrooms a 10.0kw outdoor unit may be adequate/

If all 5 indoor units are running at maximum, the out door unit will only deliver 11kw of output rather than 12kw.

However the indoor units are rarely all running at full capacity,

Also most people are unlikely to run all 5 units at the same time.

Advantages and Disadvantages of Multi Split system

Advantages

  • Good for people who have limited space
  • Much neater than having several units

Disadvantages

  • If the outdoor unit fails all the indoor units stop and you have no cooling.
  • Usually costs more to buy and install.

Why are Multi Head Systems more expensive?

Although it seems that having less out door units should save on cost there are a few reasons why that isn’t the case.

  • With the majority of systems being single head systems that makes multi head systems a special order.
  • Multihead systems are normally sold by specialist companies rather than the big box stores so there is less competition.
  • Longer pipe runs and cable runs are required rather than the typical back to back installation of the single head systems.
  • In some cases the indoor units might also require drainage pumps rather than a simple gravity drain through the external wall.

Air Conditioners – Why The Star Rating Is More Important Than Price

I’m currently in the market for a Split System Reverse Cycle Air Conditioner.

I went round a couple of the big box electrical stores last weekend and saw several models in the 3.5kw range, with prices ranging from $650 to $1,000.

But is the higher star rating of the more expensive models worth the extra dollars?

Finding Out The Savings

Well I went to www.energyrating.gov.au website to do a little investigation

I used their calculator and based my search on:

  • A 3.5kw Unit.
  • Heating for 5 months at an average of 10 hours per day.
  • Cooling for 7 hours a day for 2 months.
  • Power at $0.287 per kW hour.

The results were:

  • The best  6 Star unit would cost around $236/year to run.
  • The worst 2 Star unit would cost around $551/year to run.

That’s a huge difference of $315/year!

In other words buying the more expensive unit would be cheaper after less than 2 years!

When I decide to buy; I’m only going to be looking at the 6 Star units.

Roof Ventilation – Are Whirlybirds The Best Solution?

If you have ever been in the roof space of your house on a sunny day you will know that you very quickly start sweating!

Why it gets hot

Well the average roof size these days is probably around 200m2.

On a clear sunny day that means around a kilowatt of heat per m2 being radiated onto the roof surface.

So 200 x 1 kilowatt = 200 kilowatts of heat . . . That is a lot of heat coming into a small volume!

Even with a light coloured roof that reflects up to 50% of the heat the roof space is still going to get really hot . . . which means the inside of the house will be harder to cool.

Is a whirlybird going to help?

Go round your local DIY shop and you will see plenty of whirlybirds for sale . . . some for less than $100.

Seems cheap, not too difficult, and  no running costs, so why not fit one?

Well they may not be as effective as you hope for of several reasons:

  • Without an adequate source of incoming air, such as eaves vents or gable vents, the whirlybird will struggle to remove much air from the roof.
  • A typical whirlybird will only extract around 100-200 cubic m per hour, not enough to make a large impact when there is 200 kilowatts of heat falling on the roof.
  • On a hot still day the effectiveness of the whirlybird will be much reduced.  It needs a wind speed of upwards of 5m/sec to be effective.

Typically manufacturers of whirlybirds suggest that at least 3 will be required for a typical domestic roof. . .  so do you want your roof to be more like a factory

So what should you do?

  1. If you are still building choose a light coloured material of even plain galvanised tin to maximise the reflected heat.
  2. Make sure you have enough incoming air, such as unobstructed eaves vents, or gable vents.
  3. Consider alternatives such as

Thermostatically controlled mains powered fans (Has low running costs and will remove large volumes of air when you want it removed)

Solar Powered Fans (No running costs and most effective on sunny still days)

A final though is . . . . Installing solar power panels will provide shade for a large portion of your roof reducing the area subject to solar radiation.

 

Air Conditioning – Ducted, or Separate Units?

Guest post by Hubert Dwight

Choosing between split systems and ducted air conditioning systems is no easy task.

We understand that nagging voice in the back of your head that keeps asking “Will we go for a split systems or go for it and purchase a ducted air con system?”

Weighing up the advantages and disadvantages of both air conditioning systems is not easy and often ends up in people going for the builders standard option.

Here is some information on the pros and their cons of the alternatives.

Ducted System

Characteristics of  ducted systems are:

  • Neater with small vents, typically set in ceiling like the one on the right;
  • Centrally controllable;
  • Can have multiple zones;
  • Only one unit to maintain;
  • Air flows are less obvious in larger rooms due to several outlets;
  • You can direct the system capacity to a restricted number of zones;
  • Adjusting ceiling vents is difficult: you will need a step ladder;
  • To be effective need open doors between outlet vents, and return air inlet.
  • For larger homes you may need to Upgrade to 3 phase power;

It can be worthwhile getting a unit with variable fan speeds. . . . . . instead of ‘Low-Med-High’ other wise you may find the fan being too noisy when you are only using a a single zone.

Separate Units

System characteristics are:

  • If you only cool key rooms it can be cheaper to install and run (have units in every room running constantly and it will be more expensive);
  • Individual temperature control for each unit;
  • Ceiling space isn’t filled with ducting;
  • Individual temperature control for each unit;
  • Failure less off an issue as doors can be left open to get some cooling effect from ajacent cooled rooms;
  • Can close doors between ‘zones’ without affecting performance;
  • More intrusive appearance, and air flow is more obvious.

Combination

Can’t decide perhaps a combination system might suit you?

For instance  have ducted heating and cooling in Kitchen, Meals, Family and Theatre rooms; Split systems in the bedrooms.

Running a split system to heat or cool the bedroom is more energy efficient than running a big ducted unit.

Being able to individually control the temperatures in each bedroom is handy as children won’t want their rooms heated or cooled when you do.

Its useful you can set a split system heater in the bedroom to run for an hour or so at bedroom before shutting off.

 

Passiv Haus

What is a Passiv Haus  (Passive House)?

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)

This is much better than:

    • A typical Brick Veneer Wall – U value 0.51   (R = 1.92)
    • A typical Roof – U value 0.26   (R = 3.91)

Elimination of Thermal Bridges

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.

For more information go to the The Australian Passive House Association.

 

Energy From Sun.

Have you ever wondered why it gets so HOT in the roof space on a sunny day?

Well there is a lot of Energy coming from the Sun . . . .approximately 1.37 kw /mshines on the Earth

By the time the solar energy gets through the atmosphere to the ground it’s about 1kw/m2  for a flat surface square on to the Sun.

Even in Melbourne on an average day the typical 200m2 house will get around 8ookw hours of heat radiation onto the roof.  In January it can be almost twice as much!

Some interesting Solar Exposure Maps, like this one, are available on the Bureau of Meteorology website at this link: Solar Exposure, if you want to check the solar radiation for your location.

This shows the solar energy received in Mega Joules (MJ) on a horizontal surface. (to convert MJ to kwh multiply by 0.28).

The maps are based on measured values so they includes things like times of cloud cover.

If you follow the above link you will be able to find a map of values for each month.

 

See Sustainability for more posts.

 

Cooling Options – Add On Refrigerated Cooling

Don’t like the builder’s standard Evaporative Cooling System?

A cost effective option I have found to work well is adding a centralised refrigerated unit to the standard ducted heating.

This means both systems share the same controls, fans, ducts and outlets and will also operate for the same zones.

Some builders will allow this as an upgrade while others will want you to install the unit using your own supplier after handover.

Organising Later Installation

If you can’t get the builder to include the cooling system i would recommend you get them to do the following:

  • Contact Proposed Cooling Equipment Supplier. Find out duct size, and the power supply that your system will need.
  • Upgrade the duct sizes. Cooling systems need large diameter ducts than heating systems.
  • Provide electrical power to the site of the external unit.

This preparatory work should cost around $1,000 dollars for a single storey house but will give a much faster and neater final job.

 

A disadvantage of a central systems is it, like ducted heating, it is less effective in maintaining the required temperature in rooms that are closed off from the return air vent.

 

More about Heating and Cooling  in the ‘anewhouse Selection / Pre-Start Guide’ including 24 pages of Check Lists.