Difference between revisions of "Green Garage Solar Heating Design"

Demand Requirements

• Load Requirements / Assumptions
  • Targeting meeting 90% of space heating load
  • Design Heating Season = Nov 15 - March 15

AR: This is pretty radical to get to Nov.15 with no heat, but reportedly this was well calculated with super insulation.

• • Total Solar Heating Load = Space Heating Load + Domestic Hot Water
    • Space Heating Load = 22 million BTU per heating season; 184k BTU/day

AR: Again, by normal standards this is at least an order of magnitude low, but ...

• • • 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 (AR: I would suggest thermal is normally more like 35% to 70% efficient and about 3 or 4 times the efficiency of PV)
  • 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 (AR: I second most of the above, except square foot cost of discount Chinese evacs can be roughly equal to flat plates.)
  • Manufacturer
    

    SRCC Data for SunEarth - Empire
    • Sun Earth
      • Empire Flat Plate and Spec single glazed, copper, selective absorber |Intercept: 0.758, Slope: -0.727
      • Conversation with Bob at SunEarth on March 23, 2008
    • Others: Solar Hot Panels highly recommended, AET (STSS recommended), Solar Thermal System, Heliodyne large market share. Apricus ... the evacuated version that Roman used. (AR: We are now shifting from SolarHot collectors to Solene Cromagen - slightly better numbers and equally good pricing - just under $800 for a 4x10)
• 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 (AR: 10 panels at 55 degrees will probably create a lot of summer overheating. My first thought for this application is more like 65 to 70 degrees)
    • 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 (AR: I would recommend 5 or 8 degrees West of due South to slightly favor the afternoon sun when it is warmer with lower delta T)
    • Configuring
      • Portrait orientation
      • Parallel connection (AR: For lowest cost installation, and best efficiency with least exterior piping, I would recommend all 10 panels in one straight row, in series - Feed emerges from roof at one end. Return enters roof at other end - could not be more efficient)
      • One feeder pipe to two groups of five panels in parellel (i.e. five per manifold.) ** Thermal Capacity:
    • 23 Million BTU per heating season (Nov15 - Mar 15) See GG Solar Thermal Workbook (AR: Kudos if you can achieve this - I will take your word for it that you can.)
    • SunEarth Thermal Capacity
    • Assume
      • Full Sun: 750 BTU/sf Winter; BTU/sf Summer
      • Partly Sunny: 560 BTU/sf Winter; BTU/sf Summer
      • Cloudy: 375 BTU/sf Winter; BTU/sf Summer
  • Flow Rate: 1g/m per panel (12 g/m max): Total 10g/m...max at 30 - 40g/min (AR: When you are dealing with a drainback with no heat exchanger on the solar loop side, I feel .5 gpm/collector is adequate. I feel a full 1 gpm is wasting watts and adding wear and tear on the copper collector piping)
  • Pressure: 160 psi (AR: What is this? Max. test pressure? With drainback it is at atmospheric pressure +/-. With glycol, probably 15 to 25 psi.)
  • Temp: 15 - 25F delta T for T in vs. T out; (AR: You will probably find your T in vs. T out is under 15 especially if you have more than about .6 gpm/collector.) Max - can boil...control with the flow. Min: - above storage temp or radiant floor or indoor temp
    • Overheating / Heat dump (AR: If you use a drainback, you have a little more leeway to handle occasional stagnations (no glycol to turn acidic), but I would still recommend some overheat protection - could be a good greenhouse/tarp-roll arrangement manually raised and lowered over part of the array - or a heat dump of some sort.)
      • • He has covered the panels...often recommends doing so
        • paint the panels with poster paint that washes off (AR: Of the 3, I would have least confidence in this measure)
        • uses radiator coils with fans to dump heat
• Open Issues
  • Drainback option that eliminates glycol (AR: If possible, and I think it is, I would recommend drainback.)
  • Thermal capacity calcs...w/ domestic hot water...how many additional panels 2 vs. 3.
  • Review other panel manufacturers
  • Insulation of panels?

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
  • STSS
    • Communications with Brad @ STSS
    • Tank Sizes
  • Other:
    • American Solar Solutions Comes on a pallet and you assemble...you can get it in the basement. Comes in 800 gallon tanks with heat exchangers.
    • Design Tank Fiberglass tanks comes in sections
• Preliminary Specifications
  • Location of Storage
    • Ground floor slab in addition bldg
    • Create insulated room w/ R-25 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 2 million BTU to start (3,500 gallons)
    • Number of tanks: 1 - 3,500 gal
    • Assume 1,500 gal
  • Size: 3,500 gal = 10 ft dia x 7ft tall
  • Capacity: 470cf
  • Thermal Capacity:
    • Winter: 3500 gals = 470cf = 2.3 mBTU: equivalent to approx 13 average winter days (almost two weeks)
    • Summer: TBD
  • 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...prefer 1 tank due to cost of heat exchangers
  • 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
  • Areas: 8200sf Historic, 2xxx Annex
  • See peak load in GG Solar Thermal Workbook
• 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
  • Radiantec from Vermont
  • Others:
• 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? Winter = 90F max...summer = 68F min
  • Can radiant floor be used for cooling? Yes see ASHRAE report ... min 68 degrees
  • Plex sizing in Michigan code? Appears we can use 3/4"...1/2 min

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

• Overall
  • Overall Concept ... recommends thermal storage.
  • DOE Solar Liquid Heating
  • Solar Thermal System Calculator Surpisingly sophisticated
  • Natural Sun Heating - Mentor is Sunpower Designs from Laren Corie
  • Build it Solar - wonderful resource for everything solar
  • Dr. Shurcliff's 101 Solar Space Heating designs excellent common sense ideas for solar heating
  • Passive ZED/Solar Heating Site
  • Rushforth Solar LLC Solid consulting company in PA for solar heating.
  • The Oil Drum forum