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Renewable Heating System – Geothermal Heating + Radiant Heat + Solar Heating

Posted by Taylor Hendricksen on Jan 16, 2012 in Design | 0 comments

Renewable Heating System

Renewable Heating Systems:

The ultimate heating system would be on that is fully self sustaining and fully automated. Is this achievable you ask?

Yes, it is. By combining several renewable energy heating technologies it is not only theoretically achievable but may be more feasible that you would expect.

Geothermal Heating Systems

Geothermal heating systems are extremely efficient at the task of heating and cooling a structure. Geothermal heat pumps run on electricity. There are a few ways to generate on site electricity with solar photovoltaic being the most common residential technology. In most situations it would not be practical or cost effective to put the amount of PV panels than it would take to run a standard geothermal heat pumps system. The standard geothermal heat pump system while very efficient still uses far more electricity than is produced by residential sized PV systems. But we have to concede that if cost effective and practical were not points of motivation it could theoretically be done.

In my view the way to make the ultimate heating system more feasible is to optimize everything and add a third essential component, solar thermal collectors.

We should start with optimizing the structure. The more we can use good building techniques to minimize the thermal loads the less energy the heat pump will require to meet them. This includes passive solar design, insulation, and thermal mass characteristics.

Radiant Heat

The next thing to consider is the type of distribution system. Radiant floors with tubing on close centers is a very effective low temp distribution system. Radiant surfaces can even be in the walls or ceiling. The more surface area we have to deliver the heat the lower the temperature that is required to satisfy the load. This translates into higher efficiencies into the heat pumps which translates to fewer KWH of electricity being consumed for heat delivered.

System controls that use an outdoor temperature sensor to control the heating distribution temperature can ensure that the only the minimum required temperature is produced by the heat pump at any given time.

Solar Heating

Now for the component that really make a difference in making these systems feasible if it is integrated properly, solar thermal collectors.

A solar thermal system is an ideal component to add to a geothermal heat pump because is can always be transferring BTU’s into the earth loop. Solar thermal works best when it can deliver it’s energy into a cool heat sink. Most domestic water heating systems operate with large portions of the day where a significantly reduced or no transfer of BTU’s occur. This is because heat can only go to cold. If your solar system can only put heat into a single DHW tank it must wait until it is hotter than 120 to begin delivering energy. Then when the tank has peaked at 200 d egrees in the early afternoon the solar has nowhere else to put the energy. If the solar could deliver BTU’s into a heat sink that was 50 degrees it could do so from the moment the sun rises the moment it sets.

The efficiency of the heat pump is largely dependent on two things. Entering water temperature of the earth loop and leaving water temp of the load loop. The closer these temperatures are to one another the more efficiently the heat pump will operate. We already addressed doing things to lower the leaving water temp. The solar thermal can be used to raise the entering water temperature. There can be many ways to use the solar to do this.

As you can see on the projects page we have done this with a closed loop horizontal system out here in Montana. On that project we are putting the solar energy directly into the earth loop through a separate series of pipes. We will have data logging on it’s performance starting next winter. I will post the results and updates on that project as we get them.

In conclusion, if we optimize the efficiencies of the heat pump by integrating a solar thermal system with it, and we have a structure that has been designed to have minimal peak loads, and we optimize the distribution to be as low temp compatible as possible, then we will require much fewer KWH of electricity and we can size it’s onsite generation accordingly.