6.10 Systems

In WUFI Passive, systems consist of a set of devices. Often times, only one ‘System’ is needed per building. There are cases where multiple systems must be used, such as to add system capacity, or due to a limitation in the WUFI Passive software. More details below.

Devices must be added to cover Space Heating, Space Cooling (if applicable), Mechanical Ventilation and Domestic Hot Water (DHW).

System Coverage: If there is more than one ‘device’ serves the same purpose, both devices should be added, and the appropriate coverage must be assigned for each. Coverage can be determined based on the capacity of each piece of equipment used (i.e. if multiple different heat pumps are used with different performance ratings), or priority (i.e. heat pump for heating with backup electric resistance heaters). Coverage is assigned below the device list.

6.10.1 DHW Distribution

Domestic Hot Water (DHW)

Make sure the reviewer can verify the hot water distribution technology from the mechanical drawings. Document the actual pipe lengths used for the applicable entries described below.

Design Flow Temperature: This is used to calculate the circulation pipe losses. PHIUS will accept between 120-140oF. It’s recommended, and common, to insulate plumbing. This is mostly to improve efficiency and slow the heat transfer from the pipe to the interior environment. Although this is recommended, it is not required.

6.10.1.1 Circulation Pipes 

• Length of Circulation Pipes: A true circulation loop has hot water running through it for a certain period each day. Referred to below as ‘Continuous or time-based recirculation’. The full length of these pipes should be entered here. 
  • Recirculation systems are found most often in large or commercial buildings. 
  • For this entry, determine the length of the circulation loop. The default calculation for the recirc pumping energy auto-sizes a pump based on the gross enclosed volume of the building, and conservatively assumes 24 hour a day operation. This can be overridden. 
• On-Demand Recirculation: When recirculation is triggered by a demand-based system, rather than continuous/time-based, do NOT enter this as circulation pipes. 
  • Use the ‘Individual pipes’ entry, select ‘Hot water piping calculator’. See below. 
    • The cautious view is that an on-demand system saves water, but it does not save much water heating energy, because the pipes cool off between uses like the individual branch pipes. 
• Daily running hours of the circulation: 24 hours for continuous, or lower for time-based. 
  • PHIUS strongly discourages, but shall not prevent, the use of continuous or timebased hot water circulation systems.

6.10.1.2 Individual Pipes – Calculation Methods 

1. Simplified Individual Pipes - This method should be used for all non-residential projects. 
   1. Length of individual pipes: 
      1. To determine this, determine the distance from the HW tank/tankless heater to each individual hot water tap. Sum these distances to find the total length of individual pipes. 
      2. For hot water pipes to the clothes washer and dishwasher, exclude the length of these pipes, or more conservatively, apply a reduction factor of 0.06 to the length. 
      3. If the project is using a continuous or time-based circulation loop, determine the distance from the recirc loop to each individual hot water tap. Sum these distances to find the total length of individual pipes. (Note that a supporting drawing / diagram is part of the required documentation.) 
   2. Exterior Pipe Diameter: Typically add ⅛” inch to the nominal pipe dimension to determine the exterior dimension. Projects using a variety of HW pipe thicknesses may use a weighted average for this value. 
2. Simplified hot water piping calculator
   1. May be used early in design. Not accepted for pre-certification. 
   2. Pipe material: Select the pipe material used. More information can be found in Appendix I. 
   3. Pipe diameter: Nominal pipe diameter in inches.
   4. Number of bathrooms: Sum of all bathrooms in building covered by the DHW device in this ‘System’. 
      1. If multiple ‘Systems’ with DHW devices are defined in WUFI Passive, do not double count bathrooms. 
3. Hot water piping calculator (unit/floor method) 
   1. This calculation method is required for all residential PHIUS+ 2018 projects. 
   2. This calculator estimates hot water distribution losses, as well as ‘time to hot’ used to aid in the design of a DHW distribution network that will meet the EPA WaterSense Hot Water Delivery requirements. 
   3. The length of Demand-based recirculation pipes SHOULD be entered here. The length of time-based or continuous hot water recirculation pipes SHOULD NOT be entered in this section, but rather above under Circulation Pipes. 
      1. Hint: When considering how to enter the DHW distribution network, consider the source of the ‘hot’ water, as well as the full path from the source of the hot water to each individual tap. 
   4. For the purposes of this calculation, hot water lines to dishwashers and clothes washers can be ignored. 
   5. Sample DHW Distribution takeoff and WUFI Passive entry screen inputs can be found on the Calculators and Protocols page.

6.10.1.3 Individual Pipes – Steps for ‘Hot Water Piping Calculator’

Step 1: Choose method based on layout and distribution method.

Unit Type Method: Use for any DHW system where hot water source* reaches the individual dwelling unit. 

• Use for decentralized DHW systems i.e. 1 water heater in each unit OR central DHW systems with continuous or time-based hot water recirculation.

Floor Type Method: For semi/centralized DHW systems where hot water source* is not located at the unit. 

• Use for or semi/centralized systems with demand-based recirculation or no recirculation.

*Hot water source: Hot water heater or continuous/time-based hot water recirculation loop

----- Follow path below for method selected. -----

UNIT TYPE METHOD:

Step 2: Summarize DHW trunks → create list of each unique unit type. A unit type is designated as ‘unique’ if it has a unique DHW layout. 

• Name: Name trunk based on Unit Type (i.e. A, B, C, etc). If a single unit building, would recommend naming trunks based off ‘zones/spaces’ that the trunk serves. 
• Length: The trunk always starts at the hot water heater or recirculation loop and runs to a distribution branch. 
• Quantity: Number of times this unique unit occurs.

Step 3: Summarize DHW twigs → create a list of hot water fixtures in each unique unit type. The twig is the small diameter piping that serves an individual fixture. 

• Name: Name based on DHW tap in the unique units listed above, with a ‘T’ at the front or end. 
• Length: A twig only serves one fixture. To determine twig length, work from the fixture back to a central pipe that serves more than one fixture (branch).
  • Enter the entire twig length from the adjoining branch for each fixture no matter how many turns/twists.

Step 4: Summarize DHW branches → create list of branches connecting trunk to twig. Each twig will have its own branch, running from the trunk to the twig. 

• Name: Name based on DHW tap in the unique units listed above (same as twig but without ‘T’)
• Length: Total length between twigs and trunks above. 
• If a twig connects directly to a trunk, enter a branch with a length of ‘0’ and connect the twig to that branch. 
• Sometimes a branch off the trunk may only serve one fixture. In that case, it could all be considered a twig, or could be split into a branch and a twig. If the pipe dimension and material are the same, either method will yield the same results.

Step 5: Enter information from spreadsheet above into WUFI Passive. 

• A segment must be entered first with the trunk, then connecting branch, then connecting twig. 
• To ‘connect’ a branch to a trunk, you must first click on the trunk, then add that branch. 
• To ‘connect’ a twig to a branch, you must first click on the branch, then add that twig. 
• Be careful to ensure you are always connecting the appropriate segments.

Step 6: Use the ‘Watersense met?’ column built into the twig entries to estimate whether all fixtures will pass the EPA WaterSense Hot Water Delivery requirement. 

• This is an on-site test that applies to most residential projects. 
• This tool is used to aid in design of a DHW distribution network that will pass on-site testing, but does not guarantee it. 
• If a twig is not passing in the model, it is recommended to revise the tap location or circulation strategy for that tap.

Step 7: Double check entries: 

• All trunks must have branch entries 
• All branches must have twigs connected. 
• Quantities must appropriately represent the building distribution network.

FLOOR TYPE METHOD:

Step 2: Summarize DHW trunks → create list of unique floors, and then list each unit number on those unique floors. A floor is designated as unique if the count or configuration of dwelling units varies from another floor. 

• Name: Name trunk based on unit number (i.e. 401, 402, 403). If vertical risers, select an ‘average’ floor for unit numbers (about half-way up, see more below). 
• Length: Trunk always starts at semi/central water heater and ends at the dwelling unit.
  • On-demand recirculation loops: 
    • Enter only the Supply side of the loop, omit Return portion (downstream of last fixture and recirc pump temperature sensor.) 
    • Check the box for ‘demand-recirculation’. This will reset the ‘up-stream volume’ for any branch connected to that trunk, i.e. it will assume the branch will always be served with hot water and the trunk length should not be considered when estimating the ‘time to hot’ for the EPA WasterSense Hot Water Delivery test. 
      • The on-demand recirculation pipes must still be entered to accurately account for DHW pipe distribution losses, even though it resets the volume in the trunk for the ‘time to hot’ calculation. 
  • Vertical Risers: 
    • Determining the average vertical distance from the water heater to each unit. 
    • If all residential building: Calculating average vertical run: (# Floors * Floor-to-floor height)/2; # Floors: Includes the floor the water heater is located on, even if there are no residences on that floor.
      • Ex 1: If there are 8 identical residential floors, the water heater is in a mechanical penthouse on the 9th floor, and floor-to-floor heights are 12’, then use (9*12)/2 = 54 ft. 
    • If mixed-use building: Calculating average vertical run: ((Distance from water heater to residential floor + (# Floors * Floor-to-floor height))/2; # Floors: Do not include floor water heater is located on. 
      • Ex 2: Mixed use (floors 1-2), 8 residential floors (floors 3-11), all floors 12’ in height and water heater in basement, then use ((36’ + (8*12))/2 = 66 ft. 
• Quantity: This is number of times this unique floor occurs.

Step 3: Summarize DHW twigs → create a list of hot water fixtures in each unique unit type. The twig is the small diameter piping that serves an individual fixture. 

• Name: Name based on DHW tap in the unique units listed above, with a ‘T’ at the end. 
• Length: A twig only serves one fixture. To determine twig length, work from the fixture back to a central pipe that serves more than one fixture (branch). 
  • Enter the entire twig length from the adjoining branch for each fixture no matter how many turns/twists.

Step 4: Summarize DHW branches → create list of branches connecting trunk to twig. Each twig will have its own branch, running from the trunk to the twig. 

• Name: Name based on DHW tap in the unique units listed above (same as twig but without ‘T’) 
• Length: Total length between twig and trunk above. 
• If a twig connects directly to a trunk, enter a branch with a length of ‘0’ and connect the twig to that branch. 
• Sometimes a branch off the trunk may only serve one fixture. In that case, it could all be considered a twig, or could be split into a branch and a twig. If the pipe dimension and material are the same, either method will yield the same results.

Step 5: Enter information from spreadsheet above into WUFI Passive. 

• A segment must be entered first with the trunk, then connecting branch, then connecting twig. 
• To ‘connect’ a branch to a trunk, you must first click on the trunk, then add that branch.
• To ‘connect’ a twig to a branch, you must first click on the branch, then add that twig. 
• Be careful to ensure you are always connecting the appropriate segments. 
• Note that pipe material, diameter, and length must be added for each new segment.

Step 6: Use the ‘Watersense met?’ column built into the twig entries to estimate whether all fixtures will pass the EPA WaterSense Hot Water Delivery requirement.

• This is an on-site test that applies to most residential projects. 
• This tool is used to aid in design of a DHW distribution network that will pass on-site testing, but does not guarantee it. 
• If a twig is not passing in the model, it is recommended to revise the tap location or circulation strategy for that tap.

Step 7: Double check entries: 

• All trunks must have branch entries 
• All branches must have twigs connected. 
• Quantities must appropriately represent the building distribution network.

Four example layouts are described below:

A. Example Single Unit, On-demand recirculation (Unit Method):

Trunk: In this case, the trunk may serve rooms or ‘zones’. Check box for ‘Demand Recirculation’. 

• Bathroom Floor 1 
• Bathroom Floor 2 
• Kitchen

Branch: Starting by clicking on ‘Bathroom Floor 1’ trunk and enter each tap name off of that trunk. 

• Bathroom Sink 1 (BS-1) 
• Shower 1 (S-1)

Etc. Repeat for all trunk zones listed above.

Twig: Starting by clicking on ‘Bathroom Sink-1’, enter the twig: 

• BS -1– T Etc. Repeat for all fixtures listed above.

B. Multiple Units, Semi/Central WH, Continuous/Time-Based Recirculation (Unit Method):

Trunk: 

• Unit A 
• Unit B 
• Unit C

Branch: Enter each unique fixture type as a branch for each trunk. Example for Unit A.

• Kitchen Sink (KS) 
• Bathroom Sink - 1 (BS-1) 
• Bathroom Sink - 2 (BS-2) 
• Shower (S)

Twig: Click on ‘Kitchen Sink (KS) branch’, then add the KS twig (KS-T). 

• Kitchen Sink (KS) 
  • KS-T Click on ‘Bathroom Sink (BS-1) branch’, then add the BS twig (BS-1-T).
• Bathroom Sink - 1 (BS-1) 
  • BS-1-T

Etc. Repeat for all fixtures listed above.

C. Multiple Units, Semi/Central WH, On-Demand Recirculation (Floor Method):

Trunk: Check box for ‘Demand Recirculation’ if applicable. Length includes vertical pipe length when applicable. 

• Unit 401
• Unit 402
• Unit 403

Branch & Twig: Follow Example B.

D. Multiple Units, Semi/Central WH, No Recirculation (Floor Method):

Same as method ‘C’, but un-check ‘Demand-Recirculation’ for trunk.

6.10.2 Cooling

Cooling system properties are entered under System>Distribution>Cooling, rather than in individual cooling devices. If you are specifying varying cooling systems, add a new ‘System’, and a new device for cooling in that new system. It is not currently possible to enter varying cooling performance specifications when two cooling devices are included in the same ‘System’. 

• Coverage: WUFI Passive will estimate the available cooling coverage based on system entries. If the cooling demand is not covered, this will appear as a warning under the ‘Data state/results’ box. If the cooling demand is not coverage, capacity must be increased either by changing the numerical entries or adding an additional cooling system. 
• Cooling via ventilation air: 
  • Use this for cooling systems that cool incoming fresh air/outdoor air supply, in-line with the ventilation, and are not using additional airflow to satisfy the cooling needs. 
  • Supply air cooling capacity: From manufacturer, based on available ventilation airflow and cooling coil.
  • Supply air cooling COP: Use EER/3.412 
• Recirculation Cooling: 
  • Use for heat pump systems that cool indoor, recirculated air.
    • Recirculation air flow rate: Rated values provided by manufacturer, or estimate between 250-400 cfm/ton of cooling 
    • Recirculation air cooling capacity: Rated value from manufacturer. 
    • Recirculation Cooling COP: Use ((SEER + EER)/2) / 3.412. 
      • If only EER is provided, SEER = (1.12-√(1.2544-0.08*EER)) / 0.04
      • For commercial cooling units, the cooling COP may be estimated using the IEER rating. Use (IEER/3.412 = COP) 
      • IEER = (0 .02 * A) + (0 .617 * B) + (0 .238 * C) + (0 .125 * D) Where as:
        • A = EER at 100% net capacity at AHRI standard cond. (95 deg F)
        • B = EER at 75% net capacity and reduced ambient (81 .5 deg F)
        • C = EER at 50% net capacity and reduced ambient (68 deg F)
        • D = EER at 25% net capacity and reduced ambient (65 deg F)
• Dehumidification COP use dehumidifier rating in Liter/kWh 
  • 1 Liter/kWh = 0.625 COP 
  • OR, use a COP of ‘2’ for cooling systems that provide latent cooling as a product of sensible cooling.
• Panel Cooling 
  • Only used for radiant cooling systems. External calculation needed to determine Panel Cooling COP.

6.10.3 Ventilation Distribution

Duct Length and Duct Separation

Supply and exhaust duct lengths should be measured from the inside of the exterior wall to the outside of the ventilation unit. Often, these lengths are different.

If there are multiple H/ERVs in the project covered by a single ERV device, do not increase the quantity of duct lengths input here. For example, if there are 50 identical ERVs in the project, the ERV device will have a quantity of 50. Determine the average supply/exhaust duct length for those 50 ERVs, and input only one entry for a supply duct, and one for exhaust. Then, check the box to assign those two average-length ducts to the appropriate ERV type. This will accurately assign those ducts to the 50 ERVs.

On the outside of the building the supply and exhaust diffusers should be located at least 10 feet apart to keep from short circuiting exhaust air back into the house.

Note: If the ventilation unit is running at a very low airflow, manufacturers may allow for less separation. This will be reviewed on a case-by-case basis.

Taking the supply air from above the roof is generally not recommended, because of the possibility of excessive heat and hot-roof odor.

6.10.4 Auxiliary Energy

This should include any additional fans, pumps, air-handling units, space conditioning distribution systems, etc.

There is an option to ‘Use Default values’, which applies to many projects. 

• When this box is un-checked, only the Ventilation fan energy and defrost energy are retained. Any pump entries for DHW recirculation, storage load pump, or heating system circulation pump are removed. (Note: The devices that remain are shown in the WUFI Passive reports under Auxiliary Energy).

DHW recirculation system: Add the DHW pump energy here, or use the default value.

On-demand recirculation system for DHW: Please input the pump energy here. There is a quick workaround to determine an average estimate for this value for your project: 

1. Go to Distribution>DHW. Input a value of '1' under length of circulation pipes. 
2. Then, go back to Distribution>Aux Electricity. Note the value that auto-populates for the 'Norm Demand [W]' of the DHW circulating pump.
3. Then, go back to Distribution>DHW, remove the '1' from the length of circulation pipes. 
4. Go back to Auxiliary Energy, un-check the box for 'Use default values', and add a new pump with the ‘Norm Demand’ power rating noted from the DHW recirculating system in Step 2.

Air-Handling Units/Space Conditioning Distribution: Energy associated with space conditioning distribution networks/fans should be estimated and input here. 

• If fresh air supply is connected to an air handling unit for distribution into bedrooms, the air handling unit fan energy must be input here and assumed to run 8760 hrs/yr. See Section 3.5.3.

Direct Exhaust Bathroom Fans & Makeup Air Fans: Energy associated with fans should be input here as an ‘Other’ device. 

• Energy Demand (norm) [W]: Use fan energy data when available. If no fan energy data is available, use 0.3 W/cfm as a default. 
  • Multiply total airflow (cfm) found on Ventilation/Rooms>Exhaust ventilation by 0.3 W/cfm for [W] entry. 
• Run times are based on the assumed run times found under Ventilation/Rooms>Exhaust Ventilation 
  • Convert minutes/yr to khr/yr: (minutes/yr)/60/1000 = khr/yr.

6.10.5 Heating Devices

Heat Pumps

If any heat pump technology is used for space heating, use the ‘Heat Pump’ device type. Within this device type, there are two options for modeling heat pumps used for space conditioning: 

1. Heat Pump: Use when given a single COP (coefficient of performance) is provided for the heating system. Note that when a single value is given for air source heat pumps, often this is rated at an ambient temperature of 47F, and the entry should be de-rated if the climate often reaches temperatures below that. If only the HSPF given, COP may be estimated as HSPF/3.412. However, for colder climates, the COP is likely less than this and a HSPF de-rating calculator should be used. Download Heat Pump Protocol kit from PHIUS’ Calculators and Protocols page. Ground source heat pumps should also use this heat pump type. 
2. Heat Pump Rated Monthly COP: If COP data for two rated ambient temperatures can be found, use this device type. This takes the monthly heating demand and climate data into consideration to calculate a more accurate COP.

•  Generally, air source heat pumps are rated at 17°F and 47°F. By entering the rated performance at both temperatures, WUFI Passive can calculate an annual average heating COP based on the monthly heating demand and climate. This follows PHIUS’ heat pump protocol.

Boiler

It is acceptable, and quicker, to enter this as a “User Defined” device in the system.

Find the Energy Factor (EF) or thermal efficiency of the model you are using. 

• If using an EF, PHIUS recommends de-rating the EF by a factor of 0.92 (as in RESNET protocol), to account for the discrepancies between the heavy draws used in the DOE water heater testing protocol and the real world. This de-rated value can be thought of as a % efficiency for the boiler.

Performance Ratio of Heat Generator: Input the inverse of the efficiency (or Energy Factor)

Source Energy Factor: For natural gas, 1.1

If a specification sheet is available containing information to support the detailed entries for the Boiler device, feel free to use the Boiler option. The part-load efficiency curves in LBNL report 42175 may be used as defaults (See Figure 1 in the report for old boilers and Figure 6 for sealed combustion.)

Wood Stove

A typical “off the shelf” wood stove is likely oversized for single family passive buildings. If using this system for a portion of heating, as a default, assign 25% heating coverage. For the efficiency, an estimate of 60% will suffice. The PE factor will be 0.2 for biomass. On the other hand, if using a system designed for a lower heat load or a more low-steady heating system, such as a masonry heater or pellet stove, it may be plausible to increase the % coverage.

6.10.6 Domestic Hot Water Devices

Heat Pump Water Heaters 

• With Indoor Compressors: 
  • In the Systems branch, add a ‘Heat Pump’ device in WUFI Passive. 
  • Select ‘Heat Pump water heater (HPWH) inside’ as the device type. This will de-rate the efficiency of the HPWH heater to account for the heating systems working against each other in the heating season. 
    • Enter the heating system COP or efficiency
    • Total System Performance Ratio: Enter 1 𝐻𝑒𝑎𝑡𝑖𝑛𝑔 𝑆𝑦𝑠𝑡𝑒𝑚 𝐶𝑂𝑃 as a decimal.
    • HPWH EF: Enter the rated Energy Factor (EF) for the Heat Pump Water Heater 
• With Outdoor Compressors: 
  • Enter as a “User Defined” device. 
  • Supplemental calculators that take the local climate into effect can be found on the Calculators and Protocols page. 
  • The climate-adjusted Energy Factor (EF) of the specified model should be used
    • Total System Performance Ratio: Enter 1 𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝐸𝑛𝑒𝑟𝑔𝑦 𝐹𝑎𝑐𝑡𝑜𝑟 as a decimal. 
• Details on calculation methodology can be found in the Heat Pump Protocol linked above.

Boiler or Gas Water Heater: See above. 

• Gas Tankless: Enter the same as boiler; do not add water storage as a system. 
• Electric Tankless: Choose electric heating; do not add water storage as a system. 
• Standard Electric with Tank: Choose electric and add water storage as a system. 
• Solar Collector: In cases where the energy model report shows a solar fraction above 65%, we require a predicted annual output from the solar inspector as to the kBTU/yr energy production; OR 
  • A BEopt model run according to the PHIUS Solar DHW Fraction BEopt Protocol. This protocol can be downloaded here.

Ground Source Heat Pump

Enter as a ‘Heat Pump’ device and use the rated COP at the appropriate entering and exiting water temperatures.

6.10.7 Mechanical Ventilation Devices

Sensible Recovery Efficiency, Humidity Recovery Efficiency, Electric Efficiency: 

• PHIUS projects should model ventilation efficiency according to the protocol described by the PHIUS Technical Committee, which can be found on the Calculators and Protocols page.
• Ventilation ratings from PHIUS Certified Ventilator program take priority over 3rd party ratings. 
• Refer to the HVI Winter Ratings modified for PHIUS modeling for common ventilation units, also found on the Calculators and Protocols page. 
• AHRI ratings for commercial units do not include electrical efficiency data. For precertification calculations, estimate electrical consumption from manufacturer’s specifications. 
• Latent/Humidity Recovery Efficiency: If this value is not specified for the ERV, 40% may be entered as a default. For an HRV, enter 0%. When a project falls under the summer test conditions (Climate zones 1A,2A,2B,3B), then request the HRV manufacturer provide their CSA 439 summer test point data. You can use this to break out ASE and LR. You’ll see that most projects should use the HVI’s winter test point data. Only the 2B and 3B zones will use different test data for the ASE and LR inputs. 
• Default values may be used for performance of refrigerant-based heat recovery devices (such as CERV from Build Equinox). Or, PHIUS-approved calculation methodology may be used to determine performance entries. 
  • Default accepted values: 
    • Sensible Heat Recovery: 75% 
    • Latent Heat Recovery: 40% 
    • Electric Efficiency: 1 W/cfm

Assigning ‘rooms ventilated by this unit’: If multiple ERVs are used, the rooms assigned to each unit need to appropriately be assigned to their corresponding ERV. The list of rooms shown here is populated based on the entries on the Ventilation/Rooms branch. For the example beloiw, ERV Type X would check the boxes for all of the residential exhaust rooms. ERV Type Y would check the boxes for all common space exhaust rooms.

Quantity: When using multiple identical ERVs in one building, a single ‘Mechanical ventilation’ device in WUFI Passive can cover all of them. For example, if the project is a 50-unit MF building with 50 identical ERVs “Type X”, this can be modeled as a single device, ERV Type X, and the quantity would be adjusted to 50.

• This applies when the identical ERVs are scheduled to run at roughly the same airflow rates, and therefore would have similar rated efficiencies (refer to HVI Winter Ratings document above for more information on rated efficiencies at different airflows). 
• Because you have increased the quantity of ventilation units under the device, do not increase the quantity of ventilation ducts under Systems>Distribution (see Section 6.10.3). 
• New mechanical ventilation devices only need to be added when a new unique ERV/HRV type is used in the project. For example, in a MF building, the residential units are being served by ERV Type X, and the common spaces are served by ERV Type Y.

Defrost: No matter the method of defrost, PHIUS requires that accounting for defrost energy and entering 23 F for the temperature in which defrost must be used.

• If using a ground loop pre-heater/sub-soil heat exchanger, defrost energy does not need to be accounted for in the energy model.

Subsoil Heat Exchanger: Use for earth air tubes and liquid-based ground loops for tempering supply air. Typical efficiency ranges from 40-60%. For entries above 60% efficiency, a corresponding calculation is required for certification.

6.10.8 Renewable Energy Systems

For any renewable energy, on-site or off-site, add a ‘Photovoltaic / renewable energy’ device. 

• Use a descriptive name for the device 
• Add a new device for each unique type of renewable energy. 
• Location: Select on-site or off-site 
  • On-site: 
    • ‘Onsite Utilization’ drop-down: User Defined 
    • Photovoltaic / renewable energy [kWh/yr] : Annual system output 
      • NREL's PV Watts Calculator is an accepted method for estimating annual energy production from an on-site PV Array. 
      • Please include PV Watts report in document submission. 
    • Onsite Utilization: 1 
  • Off-site:

For pre-certification, on-site renewable energy must be documented. For any off-site renewable energy, PHIUS will as that the project owner signs a letter of intent for contracting a sufficient quantity of renewable energy before final certification is awarded.

PHIUS+ Source Zero: To determine if a project complies with PHIUS+ Source Zero, only on-site renewable energy should be entered. If the resulting source energy is ≤0, the building meets this standard. See Section 3.10.2.

6.10.9 Drain Water Heat Recovery

The drain water heat recovery device is used to adjust the temperature of the incoming water supply by recovering warm drain water and pre-heating the incoming cold freshwater.

Note: DWHR device does not work in combination with the ‘Simplified individual pipes’ hot water distribution calculation method.

DW heat recovery unit indoor temp: Default 97F

DW Heat Recovery Unit Efficiency: As rated and labeled in accordance with CSA 55.1

Pipe Length: Measured length of hot water piping from the hot water heater to the farthest hot water fixture. Measured longitudinally from plans, assuming the hot water piping does not run diagonally. Plus 10 feet of piping for each floor level, plus 5 feet of piping for unconditioned basements (if any).

Supplies pre-heated water to: Select if the system supplies both hot and cold water, or just one of the two. 

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