Question

I would like to use a geothermal heat pump in my off grid house with tubing in the concrete floor.

Asked by Vickie Westcamp
Yuba City, CA

We will begin building the house next summer, but before we get too far into the planning process, I would like to know if we can use the pex tubing in the poured concrete flooring with a horizontal geothermal system run with solar? We want to be as environmentally conscious as possible. We are also planning on having a 10,000 rain catchment system built into our roof gutters (metal roof) for irrigation of our orchard and vegetable/herb gardens. Can this be put underground so it's not ugly or does this pose problems with algae and settiment?

Answer

Vickie,

Yes, would be the correct answer to both of your questions.

Unfortunately it is not as easy as that. Below is an outline of all of the decisions which need to be made and systems which can be interconnected to achieve your environmentally conscious new home.

Geothermal System

Begin by designing a high performance envelope to reduce heat gain and heat loss.

  • Perform energy models of the proposed design to minimize heat gain and heat loss.
  • Properly design size and placement of windows to minimize heat gain through fenestration and maximize natural day-lighting to minimize energy consumption.
  • Select roofing colors which have a high SRC (solar reflectance coefficient) to minimize heat gain.
  • Consider the installation of a rainscreen exterior siding system. This will minimize heat gain and also add to the overall insulating factor of the exterior envelope.
  • Consider interconnect your geothermal system to a solar hot water system to supplement the required temperature for proper in floor heating.
  • Consider the installation of LED lighting to reduce overall energy consumption.
  • Consider installing an induction cook top to reduce heat gain from cooking and allow for the use of a small cfm range hood which reduces the overall energy consumption.
  • Install properly design window shading devises to reduce heat gain and reduce overall energy consumption.

Incorporation of these suggestions will ultimately reduce the overall size of your heating and cooling system which results in less energy consumed.

From here your solar system size can be determined based on the anticipated energy consumption.

Before designing the battery bank you will need to decide whether it will be for primary loads or for the entire home. This will greatly affect the size and cost of the battery bank required to sustain the life of the home without sacrificing your comfort.

Cistern system

It is recommended that the catchment system is placed below ground or in a dark room. The reason for this is sunlight promotes growth of algae.

You will need to install a “First Flush Valve” system prior to the cistern.

  • This valve will allow the first 1-10 minutes of water to be diverted away from the cistern allowing for the organic material and dirt accumulated on the roof to be flushed away prior to filling the cistern.
  • This will reduce the amount of sediment and organic material which would lead to algae growth.
  • Also by placing the tank below grade, depending on geographical location it may mean that you would need to drain the system during the winter month.
  • Depending on the states codes, you may also be allowed to use this water for flushing of the toilets. This would require a cleaning and treatment process.

Design

As you continue to press forward on the design for your new home, I would highly recommend that you consult with a knowledgeable Architect and energy consultants who can help you realize your dreams.

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