I had never thought much about the need to heat domestic hot water for homes or hotels – until recently.
Consider a medium sized hotel… There are boilers that are designed to heat water, to meet the maximum demand, when the hotel is full and everyone wants a shower at the same time. The boilers do their work for the few hours that are needed and wind back down. If the hotel is lucky, there are several boilers, and the demand is met by firing all at once. During off times, one boiler does most of the work. Large storage tanks hold enough water to ensure that there is never a shortage.
In normal times, in particular at night, the load on the domestic hot water system is almost zero. The boilers cycle on and off for vey short periods, simply to meet losses. These losses can mount up. There is wasted heat from the storage, and there is usually an uninsulated circulation system that pumps water around the hotel, ensuring that no guest has to wait any more than a few seconds to have hot water at the faucet. The heated pipe gives up heat to the building. In winter, this may actually help to heat the building, but in summer, it is an added load for the air conditioner. But regardless of the use, the boiler must do its job, albeit for many short intervals each day.
The worst loss, is actually not so easily seen or measured. Short cycling the boilers results in a dramatic drop in efficiency. Heat leaves up the flue, and no one is any wiser. Boilers that are supposed to be 83% efficient, generally manage to average only about 60-65% efficient on an annual basis. Most of the loss is the simply lost up the stack during the short run times that occur.
So the system is seen to be delivering hot water at an average efficiency of about 65%. But that is only the start.
Consider the use of the water… It is generally used for showers, baths, laundry, dishwashing and perhaps cooking. Every one of these uses, results in a discharge of heated water down the drain. In fact, it is likely that almost 90% of the heat that is delivered in the form of hot water is ultimately drained to the sewer.
That may seem insignificant, until one realizes that a typical hotel receives about 1/3 of its energy in electricity, 1/3 comes in as fossil fuel for building heat and another 1/3 comes for heating domestic hot water. Of the 1/3 that is used for domestic hot water, almost 90% - or 30% of the total energy that comes into the building is lost, either through efficiency (up the flue) or down the drain. When one adds to that the fact that the heating system also is about 65% efficient, that means that between 40-50% of the incoming energy is “LOST”!!!
That is staggering in a time when everyone is concerned about conservation…

<strong>Guest:</strong><br /><br />donut