A Greener, Quieter Construction Site

Posted September 29, 2008

On a construction site there is usually a generator running, producing noxious fumes and a lot of noise.  There is a greener, quieter alternative.  An idea I read about a few years ago was to use a battery bank and an inverter rather than a generator for powering tools on a construction site.  In the case I read about the builder had a bank of deep cycle batteries in his truck attached to an inverter, a device that converts the DC power from the battery to AC power that can be used by the power tools.  At night he would take the batteries back home and charge them using grid power and then return to the construction site the next day with the full batteries for another day of work.

The nature of the electrical load on a construction site is quite sporadic.  A saw is only run when a board needs cutting, a compressor only runs once in a while to recharge.  In the meantime, the generator is running all day, since the workers don’t want to be bothered turning it off and on as it is needed, so it is wasting fuel for no useful work for most of the day.   Using a battery bank and inverter, there is only a very small amount of standby loss, and the inverter only turns on when power is needed.  Since most tools are less than 15amps, a 2000 watt inverter would produce a sufficient amount of power.  If more tools are used at once, a larger inverter, or multiple inverters could be required.  The cost for this type of setup would not be a lot more than the cost of a good quality generator.

After the construction is finished, the batteries and inverter could be attached to a generator panel in the house to act as a backup power source in the event of a blackout.  A generator panel is an electrical sub-panel that feeds the critical loads in the house, such as the freezer, refrigerator, and well pump.  It includes a main breaker that can switch the power source from the electrical grid to a generator input in the event of a power failure.

If you are planning to add solar panels to the house, in either an off-grid or grid-tied setup, it would be worth considering purchasing the panels and inverter early in the building of the house in order to use them to power the construction site.  The solar panels could be mounted on a temporary mount out of harms way and the batteries and inverter put in a box to keep them out of the weather.

Posted under Methods

Tankless Hot Water Heaters

Posted September 27, 2008

A tankless hot water heater will save you 10-20 percent on your heating bill and give you a virtually endless supply of hot water.  This is possible because the tankless hot water heaters only heat the water when it is needed.  A normal tank based hot water heater will keep a set amount of water at the requested temperature at all times whether it is being used or not, so when you are not using hot water, say at night, the tank is still keeping the water hot.  Since heat always travels from hot to cold, the tank will radiate some heat into the air surrounding it, causing what are called standby losses.  Since the tankless hot water heaters only heat water when it is needed the standby losses are eliminated.

The tankless hot water heaters also use less fuel to heat the water.  A conventional gas fired hot water heater will have an efficiency of about 60%, meaning that 60% of the heat from burning the gas will be used to heat the water, the rest of the heat is lost up the chimney.  For a tankless hot water heater the efficiency is usually about 80-85%, meaning at least 20% more of the heat generated goes into the water and is not lost up the chimney.

On the downside, since the tankless hot water heater has no stored hot water, when you turn on the tap, it will take about 10 seconds longer for the system to kick in and get up to temperature than a conventional hot water heater.  This can result in more water use as you wait for the water to heat up.  If you are on a marginal well this should be a consideration.  On the other hand the water that is used while waiting for it to heat up can be captured in a bucket and used for other things such as watering the garden.  The other disadvantage is that if you have hard water, there is more maintenance involved.  The tankless hot water heater works by having a the water flow through a series of small pipes that go back and forth over a burner.  In a hard water area these small pipes will build up scale and if left untreated will eventually plug up the heater.  To avoid this you have to flush the system with a weak acid solution to dissolve the scale.  There are kits available that have a pump and an acid solution and when installed, you need to put in some extra valves and connectors to allow you to connect to the unit.  I flush my unit twice a year, once in the spring and once in the fall.

Another advantage of the tankless hot water heaters is the size.  The unit I have (Takagi TKD20) is only about 20.5″x14″x8.5″ and hangs on the wall out of the way.  In my house the same unit is used for both domestic hot water and for generating hot water for theinfloor heating.  This saves a lot of room in the utility room, as there is not tank and no furnace.  The unit I have can generate about 7 gallons of hot water per minute, so with low flow fixtures, you could have two people using hot water at the same time and still not run out.

Posted under Devices