Saturday, October 10, 2009
Considering a new water heating system? SEISCO VP says their tankless electrics offer surprising advantages
Ron right away addressed the major question of electrical supply and hot water production capacity. A SEISCO five gallon per minute unit requires 150 amp service, which has been the electrical standard since at least 1968. A modern house with its increased power supply (150 t0 200 amps) can handle a oversized SEISCO unit.
He presented a National Association of Home Builders study which showed that even in a high water usage household a tankless heater that provided 3 gallons per minute of hot water would meet household needs 98.5% of the time. A single tankless unit can provide hot water for an entire house.
Although a tank water heater can provide 50 gallons of hot water as fast as the water can flow through the pipes, once it is depleted it can't provide any hot water for a period of time. In contrast a SEISCO tankless unit can provide continuous hot water as long as you remain within its capacity.
For instance with a SEISCO unit you could have two showers (legal low flow ones not the water waster type) going 24/7, or you could fill tub after bathtub at 12 minutes per tub. Depending on the appliance you could use hot water at two to three of them simultaneously, without ever running out of hot water.
In San Antonio our auquifer water is very hard and liming is a problem for tankless heaters. Ron explained why they accumulate lime and why the SEISCO unit doesn't. Liming occurs when water is boiled. In a typical tankless unit a great amount of heat is applied to a small amount of water as it passes by the heating element(s). When the flow of water stops a small amount of water is subjected to all that heat and it boils. When it boils it leaves solids behind.
But in a SEISCO unit the heating elements do not reach such high temperatures. Instead they turn on and off every 8.3 miliseconds. All four heating elements are used at lower temperatures rather than using just one at a very high temperature. When the flow of water to a faucet stops the water left in the heater quickly cools down and does not reach the boiling point so the unit doesn't lime up.
He also addressed the "sandwich effect" that owners of gas tankless water heaters have experienced but which SEISCO units avoid. With a typical tankless unit if you step in the shower after someone has already been using hot water, at first you will get hot water, but then you will be hit with cold water followed again by hot water.
Ron said this happened because most tankless units turn on and off based on water flow. When you step in the shower after someone has just used it, the water in the pipes between the shower and the heater is hot. But when you turn the faucet the first water to flow through the unit is not heated. Its flow turns on the unit which subsequently heats the next water to flow through it, but the unheated water reaches your showerhead first delivering an icy blast sandwich between the previously heated water and the newly heated water.
But, the SEISCO unit avoids this because it is triggered by temperature not by flow. The SEISCO unit has a large water heating chamber rather than a small one. The water will not flow into the hot water pipe until it is heated, so te ice cold water sandwich is not served up.
To SEISCO their tankless heater is viewed not just as a stand alone unit but as part of a hybrid system. It might be combined with a solar water heater to provide backup or a boost if needed. It might be combined with a high efficiency heat pump water heater for times of the year when the capacity of heat pump heater is lessened (the dead of winter for instance.) It could even be placed in line to boost the temperature to provide very hot water for appliances that need it.
Since SEISCO doesn't sell gas powered units Ron was happy to point out that since electric units don't require venting, they can be installed more easily. The price comparisons are difficult to make since the relationship of the price of natural gas to electricity varies so much month to month, year to year, and with off-peak pricing for electricity even hour to hour. But the tankless electric units are price competitive to natural gas and seem to have a price advantage over propane.
But there is one application that Ron unequivocally stated would not work with a tankless electric water heater. If you have a 100% photovoltaic or wind powered home you'll need to heat your water another way. The amount of momentary peak power you'd need to generate would make it economically inefficient.