Geothermal energy can be used for hot water, heat pumps, and also to generate electricity through hot dry rock. There are, however, many variables which affect the cost of geothermal activity. While the initial price of geothermal power purchased ranges from roughly million to 0 million per MWh, there are often price escalations from year to year (one to two percent annually). This increase is entirely based on the possibility of the success of geothermal energy, on how much geothermal energy will benefit existing power companies, and how much geothermal power is going to be used.

Geothermal energy is used in over 70 countries. With the use of heat pumps it is possible to heat many homes, as well as bodies of water. The system involved includes underground pipes and loops which work with a heat exchanger and ductwork within the structure. Geothermal heat pumps can use the Earth as a coolant or a heating source. The design of the geothermal heat pump takes advantage of moderate temperatures in the shallow ground to boost efficiency and reduce operational costs. Solar heating is often combined with geothermal energy to form a geosolar system with large efficiency rates.

Geothermal hot water (hot springs) can be found underground and have a variety of uses. Water from hot springs is heated by the geothermal heat from the interior of the earth. The temperature of the earth’s rocks increases with depth (known as a geothermal gradient). If water reaches into the crust it comes in contact with these very hot rocks. The water from hot springs in non-volcanic areas is heated in this manner. Geothermal hot water can be used to heat buildings, grow greenhouse plants, for pasteurization or for fish farming.

Geothermal hot dry rock can be used to generate electricity. While geothermal energy itself is renewable, geothermal sites are not necessarily. An overworked site, or one with an excessively large energy plant, can quickly be depleted. The potential release of toxic elements also needs to be actively managed so as to minimize the impact on the surrounding environment.

When natural cracks and pores will not allow for positive flow rates of geothermal energy, high pressure cold water is pumped into the rock. This increases the rate of the geothermal energy, and the water captures the heat of the rock until it is forced out of the ground in the form of hot water. The water is then converted into electricity with either a steam turbine or a binary power plant system.

The benefits of hot water recirculation are rather obvious. You get nearly instant hot water which is convenient, and you save a substantial amount of water. But there are a few other issues to consider.

There are a number of types of recirculation systems for residential plumbing. There are the traditional full-time circulating systems that continuously pump a small flow of hot water through the piping from the heater to the fixtures and back to the inlet of the heater.

Hot water recirculation pumps are wasteful of energy

Full-time recirculation pumps are very wasteful of energy. Your water heater will have to work much harder to supply the heat needed to replace the heat being radiated from the piping system. In years past when energy was cheap and plentiful these systems were very popular, however, in today’s energy conscious environment they are becoming rare in residential plumbing systems.

There are ways to reduce the energy loss such as putting the pump on a timer to reduce the number of hours it runs.  The downside to this is that if you want hot water when the system is off, you will have a long wait and you will run a lot of water down the drain. And the system is still continuously losing heat energy while operating.

Temperature control of the pump can further reduce the energy loss from the system, but not very much unless you turn the temperature down substantially, which kind of defeats the purpose of having a recirculating system to begin with.

Troubles with Tankless

Another problem with recirculation systems is that the water flow is very low, usually not enough to turn on a tankless water heater.  This is unfortunate, since tankless heaters require even more time than a storage type heater to provide heated water to the fixtures.

Warm-water recirculating pumps

Several manufacturers like RedyTemp, Grundfos, Laing, and Watts are now offering what I like to call luke-warm recirculating pumps.  These pumps are again, low flow hot water circulating pumps, but controlled by the water temperature.

These pumps and in some cases valves are placed under the sink at the fixture furthest from the heater.  The sense the water temperature in the piping and turn on around 85 degrees F, and off at 90 degrees F. The turn on and off temperatures may vary, and some models offer the ability to adjust the temperature.

The problems are the same as using a traditional circulating system, large energy losses from circulating warm water through the piping. It’s less wasteful than the higher temperature circ systems, but still uses far more energy than a normal residential plumbing system. Since this system tends to raise the temperature in the cold water piping quite a bit since it is in the recirculating loop.

Many people do not like luke-warm cold water, and they end up running water down the drain purging the warm water out of the lines to get cold water.

Hot water demand pumps save water AND energy

The most energy efficient type of recirculating system is the hot water demand system.  The demand system pump only operates when you desire hot water. When you push the start button, or activate it with some other means such as a motion detector, the pump comes on and speeds the heated water to your fixture, sending the cooled off water from the previous use back to the heater through the cold water piping.

The pump shuts off when it detects the arrival of hot water.  At that point you can turn on the faucet and you have instant hot water. No more hot water was used than if you had not used a pump, except for the energy to run the pump itself.  The pumping energy for a typical use is microscopic. These systems typically use about .00 per year in electricity to operate.

Several companies offer hot water demand systems including TACO pump, Metlund D’mand Systems, and the RedyTemp can be operated in a demand mode as well.  Most of these systems use standard old fashioned low power low flow recirculation pumps. Metlund and RedyTemp use Taco pumps.

These manufacturers tend to provide miss-leading information about the pumps inferring that they can pump 14 and even 28 gallons per minute. That would be true if there was no pipe hooked to the outlet of the pump, but there is, and that is why many of them are not recommended for tankless heaters; they don’t pump even the ½ to ¾ gallons per minute needed to turn on the heater.

Chilipepper Sales offers the CP6000, by far the most powerful hot water demand pump on the market, and it can typically pump about 3 gallons per minute in most homes. It can turn on any tankless water heater on the market including all Bosch models, all Noritz models, all Takagi models, and all Rinnai models