Green Garage Solar Heating Design
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Contents
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
- Space Heating Load = 22 million BTU per heating season; 184k BTU/day
- See Green Garage - Current Design Assumptions
- See our GG Solar Thermal Workbook
Solar Heating System Overview
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 35% to 70% efficient ... 3 to 4 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
- 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. Solene Cromagen - slightly better numbers and equally good pricing - just under $800 for a 4x10.
- Sun Earth
- Flat Panel vs. Evacuated Tube
- Preliminary Specifications
- Size: 4ft x 10ft
- Number: 10 = area 400sf
- Positioning
- On the annex building flat roof
- Vertical Angle: 57-65 degrees per SRCC guide + Alan 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 + 5 degrees degrees for Detroit. +/- 15 degrees is ok. Site for sunrise/sunset data
- Configuring
- Portrait orientation (landscape is ok, but takes up more roof area)
- Parallel connection (see diagram Alan's Solar Collector Design)
- 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
- 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: .5g/m per collector: Total 5g/m. When you are dealing with a drainback with no heat exchanger on the solar loop side, .5 gpm/collector is adequate. A full 1 gpm wastes watts and adds wear and tear on the copper collector piping.
- Pressure: 160 psi 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; Typically 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 If using a drainback approach, you have a little more leeway to handle occasional stagnations (no glycol to turn acidic), but some overheat protection is recommended - could be a good greenhouse/tarp-roll arrangement manually raised and lowered over part of the array - or a heat dump radiator of some sort.
- Cover the panels.
- Paint the panels with poster paint that washes off ...not sure about this one
- uses radiator coils with fans to dump heat
- Overheating / Heat dump If using a drainback approach, you have a little more leeway to handle occasional stagnations (no glycol to turn acidic), but some overheat protection is recommended - could be a good greenhouse/tarp-roll arrangement manually raised and lowered over part of the array - or a heat dump radiator of some sort.
- 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.
- Insulation of panels? Not done.
- Framing for mounting the panels? Minimize roof holes...new roof design?
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
- STSS
- 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
- Location of Storage
- Open Issues
- Number of tanks? Use 1 tank due to cost of heat exchangers
- Do you need a small tank for the domestic hot water? Probably not....except for cooling season.
- What about using it for off-peak cooling storage for the geothermal? Haven't seen it done.
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
- Historic
- 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
- Conversation with Alan Rushforth on April 2, 2008
- 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