Geothermal Heating and Cooling

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Requirements

  • Backup Heating + Primary Cooling
  • Based on a "recharge the tanks" model
  • Peak Hour
    • 50K BTU Heating
    • 40K BTU Cooling
  • "Peak Day" Hour <<== used this one
    • Heating: 39K BTU per hour (using 24 hours)
    • Cooling: 14K BTU per hour (using 12 hours)

Design / Selection

  • Ideas
    • use the natural thermal effects of the basement and earth tubes to gain higher performance from the heat pump...increases Cooling EER (from 12 to 17+)...will also affect COP
    • Simplify the equipment (less is better)
  • Design
    • Air-to-Water Heat Pump
    • Earth Room
      • Purge strategy for vent capacity
      • Location: Green Garage Basement
      • Supply: 2 6" earth tubes
        • build a condensation trap
      • Exhaust: existing chimney
      • Fan
        • Located in chimney...pulls air through the room
        • use thermostat to ...determine when fan goes on
        • use ducts and hi/lo dampers in room
        • need to have fan control balance temp vs. humidity (e.g. favor avoiding condensation vs. better performance temp)
      • Thermal Mass
        • Plastic bottles (2L) full of water in room on floor and metal racks
      • Envelope
        • No organic material in the envelope system to avoid mold
        • Walls
          • 30R North and East (use rigid + cellulose)/ Zero R West and South
          • Hardie board for inside wall surfaces
          • 3 layers of rigid insulation = R30
            • Layer #1 - 2" polystyrene
            • Layer #2 + #3: 1ft - 2" polystyrene + 7ft+/- use polyiso
            • Tape joints on the inside with Kenco Tape
          • Stud 4ft on center for the framing - caulked on floor
          • caulk the floor joints (rigid to floor)
        • Ceiling
          • 40R ... use rigid polystyrene insulation
          • 8" polystyrene (4 layers, of 2" w/ staggered joints) = R40
          • Tape joints on the inside with Kenco Tape
          • Hardie board on walls and ceiling
          • caulk wall joints
        • Floor
          • Zero R
          • Seal concrete w/ DEFY concrete sealer low-VOC
        • Door
          • 36" door + rigid insulation filler - tape shut painters tape
      • Raised Equipment Platform: reuse block ... avoids flooding issues
Earth Room Plan

Rationale

  • Connectedness to the earth
  • net zero-energy
  • simplicity
  • repeatability
  • affordability