Design Evolution for HVAC Systems

Transcription

1 Design Evolution for HVAC Systems

2 What We Know Ductless Heat Pumps Reliable Efficient Having my DHP installed was as easy as falling off a log! Energy saving Can be aesthetically pleasing Give homeowners high levels of satisfaction

3 DHP Cold Weather Performance This looks scary, lets focus first on the scale on the left and legend at the bottom

4 How Hot Would You Like Your Supply Air? F Well below 0 F Warm air produced at low outdoor air temps we ll take it!

5 What We Have Learned Important Considerations Sizing and selection Heating cooling loads must be calculated Placement Homeowner education Sizing and selection Detailed capacity must be known There are BIG differences between models with same nominal size

6 The Present and Future of New Construction Stringent energy codes and legislated code cycles following in the wake of above-code programs Growing market demand for more energy-efficient and sustainable homes Heating and cooling loads dropping sharply in new homes (Yes, I said cooling) Existing technology limitations are giving way to highly efficient emerging technologies and practices

7 The Nature of Equipment Selection The goal of sizing HVAC equipment is to find the best match between the house and the equipment Optimal size is the best match, or balance, between the load of the house and the capacity of the HVAC equipment Modern, efficient homes are creating a dichotomy in which the loads don t match well with traditional, ducted equipment

8 Heating Load Inputs: It s Pretty Simple This is the old Greek formula: UAΔΤ Square Footage and R-U Values Duct Multiplier It s an educated guess Limited range in new construction ACH Almost all new homes are best matched to 40k systems Selection Process 40K 60K 80K 100K 120K 5 choices for gas

9 Heating Load Inputs: It s Pretty Simple This is the old Greek formula: UAΔΤ Square Footage and R-U Values Duct Multiplier It s an educated guess Limited range in new construction ACH This range is better, but still not good for lower load homes Selection Process 24K 30K 36K 42K 48K 60K A few more choices for HPs

10 NEEA Performance Home Pilot ~40 pilot homes across two phases, distributed across the region Full verification and commissioning 13 months of continuous metering data with extensive metering array Environmentals (temperature, RH, VOCs) HRV performance Hot water consumption and performance Heating/cooling systems performance Detailed cost data and interviews identify challenges and barriers for builders

11 BTUs Per Hour of Heat Loss Heat Loss: It s All About R-values 45,000 40,000 Heat loss through 2,000 Sq. Feet of Attic - Boise, ID 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 R-0 R-7 R-11 R-19 R-27 R-30 R-38 House size does matter, but not nearly as much as whether or not it s insulated

12 Loads Getting Lower What kind of loads are we looking at for new above-code homes? <8,000 36,000 BTU/hr. design heat load Upper end of range characterized by large homes in cold climates Homes in NEEA s pilot range from <8,000 to 18,000 BTU/hr.

13 Equipment Selection: Where We re Headed This is the old Greek formula: UAΔΤ Square Footage and R-U Values Duct Multiplier It s an educated guess Limited range in new construction ACH Lowering UA, Removing duct multiplier, lowering ACH Selection Process 24K 30K 36K 42K 48K 60K Need more appropriate options

14 Equipment Selection: Where We re Headed Great! Simpler inputs into load calcs, but DARN, now we need new selections of heat pump capacities Improved R-values Surfaces (UA) No Duct Losses Reduced Infiltration ACH Selection Process ~0-36K 24K 30K 36K 42K 48K 60K Need more appropriate options

15 DHP: Point-Source Considerations How to heat remote rooms Backup heat in bedrooms may be a good idea Home geometry and floor plan influence heat distribution

16 Central Questions About the Lack of Central Heating First Question: Will humans be thermally comfortable in the absence of a central heating system? Second Question: Are humans thermally comfortable in homes with central heat?

17 If Central Systems are Better, Please Explain the Following.

18 Heat delivery looks pretty awesome up to 15 feet and still useful up to 30 feet

19 02/03/12 15:20: /03/12 18:35: /03/12 21:50: /04/12 01:05: /04/12 04:20: /04/12 07:35: /04/12 10:50: /04/12 14:05: /04/12 17:20: /04/12 20:35: /04/12 23:50: /05/12 03:05: /05/12 06:20: /05/12 09:35: /05/12 12:50: /05/12 16:05: /05/12 19:20: /05/12 22:35: /06/12 01:50: /06/12 05:05: /06/12 08:20: /06/12 11:35: /06/12 14:50: /06/12 18:05: /06/12 21:20: /07/12 00:35: /07/12 03:50: /07/12 07:05: /07/12 10:20: /07/12 13:35: /07/12 16:50: /07/12 20:05: /07/12 23:20: /08/12 02:35: /08/12 05:50: /08/12 09:05: /08/12 12:20: /08/12 15:35: /08/12 18:50: /08/12 22:05: /09/12 01:20: /09/12 04:35: /09/12 07:50: /09/12 11:05: /09/12 14:20: /09/12 17:35: /09/12 20:50: /10/12 00:05: /10/12 03:20: /10/12 06:35:00.0 Temp F Room Temps in Low-Load House: Single Head, Distribution via HRV into Bedroom 85 Indoor temps are F ton DHP with low-efficiency HRV maintains ~70 F On ~900 kwh/year Master Guest Kitchen Office Master Closet Bathroom Living Room OAT House has low UA. Very tight. 12K ductless heat pump and low-efficiency HRV. About 900 kwh/year for space heat.

20 Sizing Variable Capacity Units When sizing variable capacity heat pumps, the minimum capacity is nearly as important as the maximum capacity When the house load drops below minimum capacity, performance drops from severe short-cycling A look at the max/min capacity at 47 F can be an indicator of how the unit will perform in these conditions We call this the unit s turn-down ratio. It varies greatly by model. Look for a unit with at least a 4:1 ratio between its maximum and minimum capacity at 47 F

21 Manufacturer's Stated Heating Capacity at 47 deg F (Btu/hr) Sizing Variable Capacity Units 25,000 Comparison of Nominal 1-ton DHP Models "Rated" Capacity 20,000 15,000 10,000 5,000 - If this house had part load needs of around 3,000 Btu/hr for much of the year, which of these systems would meet that without short cycling?

22 Manufacturer's Stated Heating Capacity at 47 deg F (Btu/hr) Sizing Variable Capacity Units 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 - Comparison of Nominal 2-ton DHP Models "Rated" Capacity Same question, would a larger system solve that problem?

23 Detailed Capacity Chart Check out the turn down ratios at 47 F, 30 F, and 15 F. It s over 4:1 at 47 F

24 Sizing Variable Capacity Units 2014 Powerhouse Dynamics Don t panic, look at outdoor temps (around 50 F). Look at power usage in gray and green spikes. Lots of cycling, 400 watts when on.

25 Sizing Variable Capacity Units 2014 Powerhouse Dynamics New control algorithms via an updated control board. See the peak watts and length of runs. Far less cycling and only using watts.

26 Boise DHP Low Output Sizing DHP Sizing Design load:24 Nom Size 24K H o u r s K low output 4K low output 3300 hrs hrs i n T e m p B i n 0 < to to to to to to to to to 59 BTU/Hr Hours in bin Boise Hours in bin Seattle 0 Check out total hours where this system will short cycle. With a 2.5:1 turndown, its 3300Hours. Its cut in half for a 6:1 turndown ratio!

27 Seattle DHP Low Output Sizing DHP Sizing K low output Design load:15 K@27F: Nom size 18K 4375 hrs H o u r s i n T e m p K low output 2810 hrs B i n 0 < to to to to to to to to to 59 BTU/Hr Hours in bin Boise Hours in bin Seattle In Seattle, short cycling total hours can be cut again by almost half by upgrading a 2.5:1 ratio to 6:1 0

28 DHP System Design Use an appropriate number of indoor heads In most homes, one head per floor is enough: An optimal system often consists of: 1 DHP in the main living area, +1 smaller unit in the master suite 1 DHP in the main living area, +1 ducted mini-split serving bedrooms 1 DHP in the main living area, plus small electric resistance heaters in the bedrooms If using ER heaters, use smaller units (750w), control with digital wall T-stats

29 DHP System Design Orient heads to take advantage of throw and mixing Place in largest, most open areas Orient to blow down central hallways In rooms with high ceilings, place DHP < 8 off the floor to minimize stratification effects Don t leave units set in Auto mode

30 Home Geometry and DHP Performance Master bedroom in singlestory home Five surfaces exposed to exterior 65 sq. ft. of glazing (26 percent of floor area) Design heat load around 2,700 BTU/hr. for this room alone

31 Home Geometry and DHP Performance POP QUIZ Q: How much 70 F air must you deliver to keep this room comfortable? A: Too much. Avoid creating thermal peninsulas unless you have an active conditioning strategy to meet the load. Room-by-room loads still matter.

32 Using Auxiliary Distribution Room-by-room loads matter and must be met In remote rooms, the heat gained through internal surfaces and delivered via distribution must outweigh the heat loss Delivering air at or near room temperature may not be enough to keep the space conditioned Supplemental backup heat doesn t transform a low-load home into an energy hog

33 It s Not a Ductless Purity Test. It s OK to Transfer Air by Other Means SPECIFICATION Volts: 120 Hertz: 60 Amps: 0.50 maximum Watts: 25 CFM: 75 RPM: 1,800 Air has a low heat capacity. Example 75F warm room 70F cool room 100 CFM 1.08 X 100 CFM X 5F= 540/BTUS/hr.

34 Using Auxiliary Distribution So, can I use an HRV or transfer fan to heat rooms? What room-to-room temp difference are you okay with? Without a high-efficiency HRV, you will be cooling during the heating season Ventilation air typically can t meet room loads alone They only recovers and/or move heat. They doesn t make heat.

35 Ducted Mini-Split Design Select equipment with at least a 4:1 ratio between its maximum capacity and minimum capacity at 47f Place and orient indoor heads to allow for future maintenance/service Closets and dropped ceiling are good options Locate ducts and equipment in conditioned space

36 Ducted Mini-Split Design Good duct design is key Adhere to manufacturer s guidance some specify ducting limitations for their units, others just provide static pressures for the fan Do a real duct design follow Manual D guidance or use the Easy Ducts process Design and install to minimize restriction Use grilles that will throw and mix well Use with a wall-mounted T-stat Locate T-stat appropriately Make sure controls reflect the necessary settings

37 Ducted Mini-Split Design

38 Ducted Mini-Split Design FUNCTION 42 and Other Settings Setting the unit to sense temperature at the T-stat: Function 42 has to be set to 01 and the t-stat icon has to appear on the screen High Insulation setting needs to be activated

39 Using an HRV to Ventilate and Distribute into Bedrooms HRV Ratings: Which Three-Letter Acronym Matters? Sensible Recovery Efficiency (SRE): The efficiency including the energy use of the system. This value is used principally to predict and compare energy performance. Apparent Sensible Effectiveness (ASE): The efficiency not including the electrical energy used by the system. This value is useful principally to predict final delivered air temperature. We recommend high-ase HRVs as it relates to delivered air temperature. People WILL shut off HRVs that blow cold air on them!

40 Delivered Air Temp About that ASE Delivered Air Temp at Various Outdoor Temps and ASE 75 Use HRVs with high ASEs (over 85%, ideally) to deliver proper air temp Outdoor Air Temp 60F 40F 20F 0F Apparent Sensible Efficiency

41 Conclusions Net Zero, low load, above code homes, are no longer a niche market in the Northwest Low loads don t make the home comfort invincible The best system in the world does nothing if it isn t used properly Homeowners must be educated on the operation of systems in their homes

42 Advice to Homeowners Leave interior doors open Clean filters Check drain pains NEVER use auto mode Don t make big changes in the set points

43 Thank you GoingDuctless.com/partners