Building Construction, Renovation & Maintenance

Bigger Is Not Always Better

Correct Specification of Sizes

When we are constructing a building there are many occasions when it is important to select the correct size for the design of buildings and the equipment and fittings we use. The size of water pumps, air conditioners, and water heaters, the size of bedrooms, garages, the size of reinforced concrete columns and beams, the height of ceilings, size of bedrooms and depth of swimming pools, the list goes on and on.

Getting these sizes correct is important, if the size is too large we will probably pay more, sometimes a lot more, and if it is too small the item may not be fit for purpose. If concrete columns and beams are to small a building might be dangerous to the point of being life threatening.

Here we look at oversizing some examples of common items such as air conditioners and water pumps.


See the full Fixed Abode article "Never Mind The Quality Feel The Width" here


Is bigger really better?

Anyone who has tried to crack a walnut when all they had available was a sledge hammer knows that it is not easy, there is a tendency to pulverise the contents.

In the same way if someone puts a huge great water pump on your roof powerful enough to empty the bilges of the Queen Mary in order to push a bit of water to your shower there is a likelihood of the force of water removing your skin to say nothing of the risk of drowning. There are other disadvantages. The deep rumble of the pump can be heard 3 miles away, not conducive to a spot of yoga, and the electrical bills become excessive to say the least.

What is not quite so obvious is that, from a technical point of view, a large pump to do a small job has a particular problem – it pumps too much water. It is rather like getting a gorilla to ice a cake, one small squeeze and there is icing all over the cake, the table and the floor.

When you turn on a shower the pump starts but, if the pump is too big, the water can’t get out of the shower head fast enough, the pressure builds up and the pump stops. A split second later the shower has caught up so the pump starts again. And so on ad nauseum. The water coming out of the shower “pulses”. You know what I mean, one minute the water is bouncing off the far wall of your bathroom and the next it is dribbling on the floor.

So this huge great pump is starting and stopping constantly putting an enormous strain on the pump, the pipes and the roof. Pumps like this have a way of getting totally fed up, breaking their anchor bolts and going for a walk and a half ton pump walking off your roof is no joke.

But no one would install such a ridiculously large pump would they?

Well you would think not but the other day I saw such a pump. In fact two pumps.

Why? Who knows.

Perhaps if you are a contractor and you can persuade your client they need a pumping system costing $7,000 why sell them one for only $500? But then an expatriate designed this system. Perhaps he didn't understand what he was doing and thought he would overengineer “just to make sure”, perhaps he was an enthusiast on pumping systems and got a bit carried away or perhaps he had just received one too many of those emails, his manhood was challenged so he just had to prove that bigger really is better.

Are you looking for a bilge pump for an ocean liner? Perhaps a battleship? I know a nice lady who can help you out.

The same lady has an electrical system in each of her four houses suitable for controlling Blackpool Illuminations. Once again gross over specification.

The lesson in all this is that if you are having a house built or having equipment installed it is important to make sure the specification suits the job in hand. If in doubt look at the price and if it looks on the high side get it checked out.

Air conditioners are a case in point. While many people get along with air conditioners that are too small for the room they are in some people believe bigger must be better. Be careful, it is not a good thing to install an air conditioner that is too large. If you do, like the waterpump, the air conditioner will keep switching on and off and drive you nuts.

In fact in many cases it may be that using several small units is more advantageous than a single large unit. Let me give you an example. In many modern hotels you will notice that these days the rooms are cooled by independent air conditioners rather than the large single “industrial” unit of old with ducting to each room. These domestic units take advantage of the benefits of mass production and are low cost compared to large industrial units. Such a system has great flexibility and should one unit break down the whole system is not put out of action and it is not a serious problem. In addition further down the track you don’t have to replace the whole system at once so upgrading can be done progressively.

Years ago I was designing a computer system for managing supplies in a major hospital in Australia. At the time I surprised people by specifying networked desktop PCs. At the same time a neighbouring hospital decided to go for a small mainframe computer which of course cost many times more both in hardware and the special “one off” software programs it required. The PCs and their software provided a far cheaper, more flexible and easily upgradable system which eventually was installed in hospitals throughout the state. The mainframe was a disaster. As expected within only a few years desktops had developed to the extent that they had more power than the original mainframe anyway.

So what is the relevance of all this? Well if you are installing systems you might consider using small multiple systems rather large individual ones. If you have ten villas with twenty bathrooms it may be advantageous to have individual water heaters for each bathroom, separate pumps for each villa, multiple air conditioners for large spaces. You can always add extra units later to increase capacity and maintenance costs tend to be staggered while a single repair to a large central unit may make you stagger.


Copyright © Phil Wilson August 2007
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