Ducts in Conditioned Space High Performance Attics

Transcription

1 2016 Title 24 Codes & Standards Enhancement (CASE) Proposal Ducts in Conditioned Space High Performance Attics May 8, 2014 Matt Christie (TRC) Abhijeet Pande (TRC)

2 Stakeholder Meeting: Agenda Code change overview Summary of current code requirements Typical practices Initial data and findings Methodology for analyses Proposed code requirements Specific stakeholder requests 2

3 Proposed Code Change Overview Why are we proposing this measure? Align with California's ZNE goal for residential new construction by 2020 according to the loading order Minimize building loads Reduce HVAC equipment size Source: HMG

4 Proposed Code Change Overview Why are we proposing this measure? Reduce energy impacts of cold ducts in hot attics Reduce attic temperature Install well insulated, well sealed ducts and A/C equipment in attic Make the attic part of the conditioned space Move ducts and A/C equipment out of the attic as feasible 4

5 Proposed Code Change Overview Prescriptive Package(s) Ducts in Conditioned Space (DCS)* High Performance Attic (HPA) Packages include a combination of the following: Insulation location: above or below roof deck; ceiling Insulation levels Duct location, insulation, and sealing Air handler location * Ductless systems as alternative to DCS 5

6 Proposed Code Change Overview First Prescriptive Option Ducts in Conditioned Space (DCS) Vented Attic Strategy Dropped ceiling Conditioned plenum space Open-web floor truss (for 2+ story homes) Conditioned/Unvented Attic Strategy Ductless Systems as an alternative 6

7 Proposed Code Change Overview Second Prescriptive Option High Performance Attic (HPA) Roof deck insulation above or below deck in addition to ceiling insulation Increased duct insulation Lower duct leakage rate Potential Additional Measures Raised heel or extension trusses Lower duct surface area in unconditioned space 7

8 Current Code Requirements 2013 Title 24 Requirements Mandatory Duct leakage rate: 6% verified Prescriptive Package Requirements Ceiling insulation: R-30 (CZ 2-10) or 38 (CZ 1,11-16) Duct insulation: R-6 (CZ 1-10,12,13) or R-8 (CZ 11, 14-16) 8

9 Current Code Requirements 2013 Title 24 Performance Approach Standard Design Assumptions Ducts and equipment located in unconditioned space 100% in attic for single-story 65% in attic/35% in conditioned space for 2 or more stories Supply duct surface area is 27% of Conditioned Floor Area 1 to 300 free ventilation ratio; higher with whole house fan 9

10 Current Code Requirements 2013 Title 24 Performance Approach (continued) Available Compliance Options Ducts located outside of the attic Roof deck insulation: above- and below-deck Verified installation of Low Leakage Air Handler Higher duct insulation (than prescriptive) Raised heel truss Verified duct design layout for reduced duct area 10

11 Current Code Requirements 2012 IECC for comparison Ceiling insulation: R-38 for most of CA Allows R-30 if insulation uncompressed at edges (i.e. raised heel truss) Supply ducts insulation R-8 in attic Duct sealing (Mandatory): Total leakage shall be 4 cfm25 per 100 s.f. CFA For a 2100 sf home with 3.5 ton system, matches 6% duct leakage requirement in Title 24 Air handlers shall have an air leakage of 2% of design air flow rate 11

12 Typical Practice Current CA standard practice Ducts and equipment in vented, unconditioned attic Duct insulation is a mix of R-4.2, R-6 and R-8 Measured duct leakage rate consistently less than 6% Insulation at the ceiling 12

13 Current High Performance Practice High performance practices for homes in CA Builder experience Some builders have made roof deck insulation standard practice Others (including major builders) are experimenting with various roof deck insulation, duct location strategies PG&E program efforts ET program: installing and field testing of plenum, dropped ceiling and sealed attic strategies ZNE demonstration: installation and monitoring of dropped ceiling with condensing furnace SCE Emerging Technology Program Installed and monitored performance of sealed attic with ductless mini split system 13

14 Current High Performance Practice - Examples Project Type Roof/Ceiling Ducts & Indoor Equipment CZ Status Production Bldr Production Bldr Production Bldr Production Bldr Production Bldr conditioned plenum (using modified truss) Indoor mechanical closet with ducts in conditioned plenum 13 conditioned attic (spray foam under deck) ducts and furnace in conditioned attic Various conditioned plenum conditioned plenum dropped ceiling Starting construction on five homes Have been building this way since 2011 Indoor mechanical closet with ducts in conditioned plenum 11 Under construction furnace in interior closet or vented attic with ducts in conditioned plenum Various ducts in dropped ceiling projects; considering open web floor truss 12 production advanced houses production advanced houses Production Bldr Spray foam below deck mini-splits (ductless) 10 ZNE production house DOE Challenge Home Conditioned attic (blown-in below roof deck) ducts and furnace in conditioned attic 10 construction complete R-11 batt below roof deck; Modified existing house R-38 ceiling insulation R-8 attic ducts; 4% duct leakage 12 construction complete conditioned plenum Indoor mechanical closet with ducts in considering another Demonstration House (using modified truss) conditioned plenum 13 test house Demonstration House conditioned attic (spray foam below deck) ducts and furnace in conditioned attic 12 SMUD Home of the Future Demonstration House conditioned attic (spray foam below deck) ducts and furnace in conditioned attic 12 Demonstration House SIPs roof NA 12 Demonstration House dropped ceiling ducts and handler in dropped ceiling 13 SMUD Home of the Future SMUD Home of the Future ZNE demonstration house 14

15 Initial Data and Findings - Summary DCS encompasses a variety of design options DCS is aligned with CPUC s ZNE goals and is implemented for high performance buildings Some production builders in CA have experience with DCS/HPA implementation Low current market penetration for DCS and HPA strategies builders in the US that are building NZE homes, or are on that path, are all moving their ducts into conditioned spaces. (It s not just for those in mild climates.) Sonja Winkelmann, Executive Director of Net-Zero Energy Coalition 15

16 Ducts in Conditioned Space Concept: moving ducts and air handler to conditioned space Recap ~ Ducts in Conditioned Space (DCS) Vented Attics dropped ceiling, including soffits conditioned plenum space open-web floor truss Conditioned/Unvented Attic Ductless Systems 16

17 DCS Vented Attics Dropped Ceiling conditioned space for ducts b/n ceiling plane & dropped ceiling Source: 17

18 Example: DCS Vented Attics Dropped Ceiling Source: BIRA Energy,

19 Example: DCS Vented Attics Dropped Ceiling Source: Steven Winter Associates, Inc

20 DCS Vented Attics Conditioned Plenum Space conditioned space for ducts and equipment above the ceiling plane (use of plenum truss is one option) Source: Source: CEC Report Costs & Savings For Houses Built With Ducts in Conditioned Space

21 Example: DCS Vented Attics Conditioned Plenum Space Source: Steven Winter Associates, Inc

22 DCS Vented Attics Open-Web Floor Trusses conditioned space for ducts b/n vertical space create by floor trusses Sources: Source: Steven Winter Associates, Inc

23 Ducts in Conditioned Space Air Handler in Mechanical Closet Use mechanical closet within the thermal boundary for AHU & equipment; Select sealed combustion furnace with combustion air ducted directly into the furnace Source: IBACOS, Inc Source: David Hales, WSU 23

24 Summary - DCS Vented Attics Benefits Incremental changes to standard practice vented attics Multiple buildable options Moving ducts out of hot attics Potential to downsize equipment Design/Construction impact Need to seal the soffit/plenum/floor truss perimeters May need mechanical closet for air handlers 24

25 DCS Conditioned/Unvented Attic Use above- or below-deck insulation as a primary insulation Source: 25

26 DCS Conditioned/Unvented Attics Benefits Lowering attic temperature Potential to downsize equipment No need to seal ceiling plane (can lighting, sprinklers) Design/Construction Impact Need to address moisture management (similar to HPA options) Need to seal attic-to-deck junction Use of sealed combustion equipment Observations and findings Done correctly attic temperature within a few degrees to directly conditioned space No documented moisture issues in California 26

27 Alternative: Ductless Systems System types Mini-splits Hydronic Packaged terminal heat pump Benefits Elimination of duct losses Higher system efficiency No need for DCS or HPA measures Observations and Findings Limited design, installation and maintenance experience in CA Source: Manufacturer website Daikin Source: BPA Ductless Mini-split HP webpage 27

28 High Performance Attics (HPA) Concept: reduce attic temperature in vented attics Recap ~ Proposing a package of measures including one or more of the following: a. Roof deck insulation: above or below deck b. Increase duct insulation c. Lower duct leakage rate (Potential additional measures) a. Raised Heel Trusses or Extension Trusses b. Reduce supply duct surface area 28

29 HPA Roof Deck Insulation Install insulation above or below roof deck, including gable walls Source: Source: BSC

30 Above Deck Insulation Product types Polystyrene: EPS (expanded) and XPS (extruded) Polyisocyanurate Polyurethane Industry discussions Roof product fire rating Roof product attachment and ventilation Moisture management Source: BSC

31 Below Deck Insulation Product types Batt insulation Loose fill, blown-in Open cell and close cell Spray Polyurethane Foam (SPF) Each requires different construction technique and is at various cost points Industry discussions Moisture management Roof product fire rating Source: BSC 2012 Source: BSC

32 HPA Increase Duct Insulation Proposal: R-8 in all CZ Benefits Little change in installation practice minimal incremental costs, once it is more widely available Design/Construction Impact Size and maneuverability of ducts Observations and Findings Transition from R-4.2 to R-6 as standard practice, and increased use of R-8 is already taking place Source: 32

33 HPA Lower Duct Leakage Proposal: Lower allowed duct leakage rate to 4%- 5% Benefits Potential air quality improvement Design/Construction Impact Increases use of low leakage air handler Requires better installation practices Observations and Findings Standard duct installations in CA often meet or exceed the 6% duct leakage requirement Source: 33

34 HPA Potential Measure Raised Heel or Extension Trusses Proposal: No compression at insulation edge with raised heel or extension trusses Benefits Helps realize full benefit of insulation Design/Construction Impact Low level of installation experience in California Observations and Findings Other methods to achieve the same outcome include framing with a rafter on raised top plate or utilizing spray foam or rigid foam at the edge Source: Building America Solution Center (2013) 34

35 HPA Potential Measure Reduce Duct Surface Area Proposal: Efficient duct layout design in unconditioned space to eliminate excess lengths of duct runs Benefits Improved design and better air flow Reduced material costs Design/Construction Impacts Requires verification Current compliance is burdensome Practicality of field verification Observations and Findings Some builders already utilize the compliance credit Ducts are not always installed as shown on plans F - 1 F - 1 Improved Design shorter total lengths, more streamlined layout Standard Design 35

36 Summary of HPA for Vented Attic Reduces attic temperature Incremental changes to standard practice No change to duct and air handler location Package of measures will provide similar savings as having ducts in conditioned space CASE team is investigating the right mix of measures to ensure HPA gets same savings as DCS 36

37 Moisture Management: Above- deck insulation Issue: moisture-laden air could infiltrate through the joints in the insulating sheathing to the deck Solution: install an air control membrane to prevent the moist air from reaching the wood decking Rigid insulation Source: BSC

38 Moisture Management: Below- deck insulation Vented attic Air permeable insulation may be installed under the roof deck in vented attics without moisture issues in all climate zones but CZ16 Conditioned/Unvented attic Prior studies show assemblies have drying capacity to handle minor rainwater leakage; confirmed via field assessments Various options to handle indoor moisture 1. Use impermeable insulation, OR 2. Use permeable insulation below deck and at least R-4 above deck OR 3. Use air impermeable insulation below and in direct contact with roof deck, then air permeable insulation directly below that 38

39 Sheathing Moisture Management Issue: Industry concern that deck insulation may impact drying in the case of failure regardless of whether for vented or conditioned/unvented attics Findings: APA technical bulletin suggests ways to prevent issues in conditioned/unvented attics Install roof and flashing systems properly Maintain good building and HVAC system conditions Provide the roof system a means to dry in the event of moisture accumulation 39

40 Deck Insulation Interaction with Roofing Products Shingle Roof: Industry concern that higher shingle surface temp due to deck insulation may reduce product service life (by 10% on conditioned/unvented attics) Solution: use spacers to provide ventilation for shingles Tile Roof: Industry concern that above-deck insulation reduces natural ventilation below roof tiles Solution: use counter batten that raises tile to increase ventilation Fire Rating: Industry concern on deck insulation affects fire rating Solution: above-deck rigid insulation and SPF products meet flame spread speed and smoke developed index requirements, certified by ICC-ES via Evaluation Service Reports (ESR) 40

41 Ventilation for Shingles with Above-Deck Insulation Use wood sheathing to provide nailable base for shingles Some existing above-deck products come with nailable base Use spacers to create channels of continuous ventilation Source: ARMA

42 Ventilation for Tiles with Above-Deck Insulation Use counter batten (vs. single layer batten) to provide more air space for ventilation Source: Tile Roof Industry presentation at CBIA Forum 42

43 Examples Fire Rating Info: Polystyrene and Polyiso Rigid Foam 43

44 Example of Fire Rating Info: SPF 44

45 Methodology for Savings Analysis Energy and Demand Impacts Use CBECC-Res simulation software Two Prototype Buildings 2,100 sf single-story 2,700 sf two-story Baseline: minimally meet 2013 prescriptive package requirements Evaluate individual measures as well as in packages 45

46 Proposed Code Requirements Section 150.1(c)9 9. Space conditioning ducts distribution systems. All space conditioning systems shall reduce distribution losses by complying with items A or B below: A. High performance attics. Air handlers or ducts are allowed to be in unconditioned spaces or vented attic spaces when the attic and ducts meet all of the following requirements: i. Ducts and air handlers shall be sealed to a leakage level of no more than 4% of rated of nominal airflow as tested in accordance with Reference Residential Appendix RA ii. All ductwork in unconditioned spaces shall be insulated to at least R-8. iii. If any portion of the duct work or air handler is in an unconditioned attic, then the roof deck of the attic and gable walls be insulated to at least R-6 (note: actual standards language is in terms for U-factor. CASE team will specify U-factor in the final code language) iv. The attic shall incorporate energy truss to allow full height of uncompressed insulation to extend over the wall top plate at the eaves v. Other addition requirements TBD 46

47 Proposed Code Requirements A. Ducts and air handlers in conditioned space. (details on previous slide) B. Duct and air handlers in conditioned space. Duct work and air handlers of HVAC systems shall be in conditioned space. Complying systems include either item i or ii. i. HVAC systems where air handlers and all duct work are in conditioned spaces. Ducts and air handlers shall be sealed to a leakage to outdoor level of no more than 10 cfm at 25Pa as tested in accordance with Reference Residential Appendix RA If the air handler contains a combustion device, the device shall be a sealed combustion device. ii. Ductless HVAC systems including but not limited to: ductless mini-split systems, hydronic heating and cooling systems, package terminal and sealed combustion through-the-wall furnaces. 47

48 Requests from Stakeholders We Want to Hear from You! What is builder preference for duct location: Dropped ceiling, conditioned plenum, or scissor trusses? Why? Any concerns or feedback regarding HPA measures? Are there benefits or challenges we identified that are no longer applicable in current market? Will any construction strategies become more prevalent in near future, and why? More comprehensive questions posted on outreach website: 48

49 Questions? Matt Christie 49