Green Garage Solar Heating Design

From Green Garage Detroit
Revision as of 15:48, 30 March 2009 by Tom Brennan (Talk | contribs) (Solar Heating System Overview)

Jump to: navigation, search

return to Solar Heating Design

Demand Requirements

  • Load Requirements / Assumptions
    • Targeting meeting 90% of space heating load
    • Design Heating Season = Nov 15 - March 15
    • Total Solar Heating Load = Space Heating Load + Domestic Hot Water
      • Space Heating Load = 22 million BTU per heating season; 184k BTU/day
      • Domestic Hot Water Load = 120 gals / day
  • See Green Garage - Current Design Assumptions
  • See our GG Solar Thermal Workbook

Solar Heating System Overview

Green garage Solar Heating Schematic - V5

Solar Thermal Collectors

  • Goal = highest Heat Output / Total Life-cycle Cost
    • Should BTU generated per dollar invested...why not just buy little more of a slightly lower efficient panel that is much less expensive and get same total energy.
    • where Heat Output (Q-out) = Temp Rise x Volume Flow Rate x Specific Heat of Water
  • Basics Guidelines
    • Solar thermal (liquid) panels are up to 80% efficient ... 5 to 10 times that of PV panels
    • The efficiency varies greatly with delta T (Tin - Tout)the greater the difference the lower the efficiency
  • Solar Collectors
    • Flat Panel vs. Evacuated Tube
      • Choose: Flat panel because of lower cost (approx 1/3 the cost) and higher durability (twice the life)..performance usually better in the system vs. on the testing bench
    • Manufacturer
      SRCC Data for SunEarth - Empire
  • Preliminary Specifications
    • Size: 4ft x 10ft
    • Number: 10 = area 400sf
    • Positioning
      • On the annex building flat roof
      • Vertical Angle: 55 degrees per SRCC guide the panels should be (Latitude + 15 degrees) for winter heating driven systems
      • Horizontal Angle: solar "true" south - determine at site...slightly west of magnetic south...estimated to be approx + 4degrees degrees for Detroit. +/- 15 degrees is ok. Site for sunrise/sunset data
      • Configuring
        • Portrait orientation
        • Parallel connection
        • One feeder pipe to two groups of five panels in parellel (i.e. five per manifold.)
    • Thermal Capacity:
    • Flow Rate: 1g/m per panel (12 g/m max): Total 10g/m...max at 30 - 40g/min
    • Pressure: 160 psi
    • Temp: 15 - 25F delta T for T in vs. T out; Max - can boil...control with the flow. Min: - above storage temp or radiant floor or indoor temp
      • Overheating / Heat dump
          • He has covered the panels...often recommends doing so
          • paint the panels with poster paint that washes off
          • uses radiator coils with fans to dump heat
  • Open Issues
    • Thermal capacity calcs...w/ domestic hot water
    • Review other manufacturers

Thermal Storage

  • Demand Requirements
    • Space heating and domestic hot water. We're investigating cooling ideas.
    • Goal is, practically speaking, 90% with a retro fit...no opportunity for below floor storage.
    • 10 gallons ( or approx 1 cu ft) for every 1 sf of solar panel if you want to get to near 95% of heating demand
    • Hold four days of heat (Rushforth LLC uses 2+ days... and gets much better results than one day)
  • Basic Guidelines
    • Place storage indoors...not outdoors, because heat loss indoors helps heat the building.
  • Manufacturer
  • Preliminary Specifications
    • Location of Storage
      • Basement on south end: 18' wide x 20' long x 10' high
      • Create insulated room w/ R-45 walls + R-25 floor + R-25 ceiling
    • Thermal Architecture
      • All heat generators (i.e. solar and geothermal) connected to the storage
      • All heat consumers (i.e radiant heat and domestic hot water) can draw heat from storage via heat exchangers.
    • Size of storage
      • Store 1 million BTU to start (2,000 gallons) (note: if we can find an affordable 4,000 gal answer that would be great.)
      • Number of tanks: 1 (3,000 gal) or 2 (1,500 gal)
      • Assume 1,500 gal
    • Size: 2,000 gal = 7.5 ft dia x 6ft tall
    • Number: 1
    • Capacity: 400cf
    • Thermal Capacity:
      • Winter: 3000 gals = 400sf = 2 mBTU: equivalent to 11 average winter days
      • Summer:
    • Thermal Loss: R-19 around tank
    • Flow Rate: Max 15g/m ... geothermal connection
    • Pressure: Sealed, non-pressurized
    • Fluid: Water...no additive
    • Temp: Max: 175F Min: above radiant floor or indoor temp
  • Open Issues
    • Number of tanks?
    • Min temp from a systems design standpoint...not a tank material standpoint?
    • What about using it for off-peak cooling storage for the geothermal?

Radiant Floor

  • Demand Requirements
  • Basic Guidelines
    • Only 10% of heat is lost through the floor...42% through the roof
    • Radiant heats up to about 7ft from the floor
  • Manufacturer
  • Preliminary Specification
    • Zones: approx 1100sf; 8 - Historic; 2 - Annex
    • Circuits: 6 per zone
    • Plex: 1/2in
    • Spacing: 8in
    • Flow Rate: 4.5 g/m
    • Temp: normal winter operating 90F; max = 130F
    • Thermal Capacity: 38,000 BTU/hr per zone
    • Floor architecture
      • Historic
        • Vapor barrier or sealer (10mm?)
        • Two layers of 1" XPS with seams staggered and sealed. (2")
        • Reflective radiant barrier (could be foil on the XPS?) (mm)
        • Sleepers (1.5") with metal heat extenders
        • Plywood? Wood Flooring (1")
        • All screwed together, run trenches
  • Open Issues
    • Normal operating temps winter...summer?
    • Can radiant floor be used for cooling?
    • Plex sizing in Michigan code?

Geothermal

  • Preliminary Spec
    • Location: Basement
    • Connect Geothermal to with open loop to the mass storage
  • Manufacturer
    • Water Furnace...Envision
  • Open Issues
    • Geothermal - operating temps (min-max)

Resources