Fresh Air Ventilation
An airtight, low-energy building in this climate should include dedicated mechanical ventilation with heat-recovery in order to deliver enough fresh air for good indoor air-quality (IAQ) in all seasons.
It is important not to over-ventilate a building in winter, otherwise over-dry indoor air and associated health concerns can result. In order to help reduce airflow rates while still maintaining good indoor air-quality, we recommend using a Supply- Transfer-Extract configuration rather than supplying and extracting from each individual room. Supply air should be provided to bedrooms and living spaces, while extract air should be drawn from bathrooms, the kitchen, and any storage spaces. Transfer openings (door undercuts, transfer grills, etc…) should be provided between supply and exhaust spaces.
This configuration reduces the potential for any duct-born sound transmission between spaces, ensures a good mixing of the fresh air supply, and reduces the size, complexity and cost of the ducting required.
It is critically important that the fresh-air ventilation system be installed such that it is completely independent of the heating/cooling system. There is no effective method of combining the fresh-air ducting along with the heating/cooling ducting, and so planning should allocated sufficient space for both ducting systems.
Fresh Air Flow Rates
In order to establish good airflow rates for the building which both provide sufficient fresh-air but do not over-ventilate, we recommend a three-part test for sizing fresh air ventilation flow-rates to individual spaces. The larger of the three resultant flow-rates should be used as the design flow rate when selecting an appropriate E/HRV model.
1. Test for Minimum Supply air flow rate:
Flow rates should be based on a standard 18 cfm/person occupancy. The occupancy is based on a ’typical’ 375 sf/person rate unless otherwise specified. This flow rate is designed to provide good indoor air-quality without causing excessive energy-loss or over-dry air (winter) or excess humidity (summer).
2. Test for Minimum Extract air flow rate:
Based on the space usage (Kitchen, Bath, Storage, etc..) establish minimum extract rates. These rates should be as follows: 36 cfm/ kitchen, 26 cfm/full bathroom, 12 cfm/storage or utility room.
3. Test for a Minimum whole-building ACH @ 100% fan speed:
The minimum flow rate for any building should be 0.39 ACH in winter at 100% HRV fan speed. This is for hygienic reasons, even if the occupancy or space usage would lead to a smaller flow-rate this minimum takes precedence.
The largest of the above values should be used in order to establish target design flow-rates for the building. We have evaluated the building using this method and recommend fresh-air flow rates according to the schedule below.
Ventilation Components
For this home, we recommend a high-performance H/ERV with better than 75% heat recovery. The Zehnder America ComfoAir Q450ERV/Q350ERV would be good selection and provide excellent indoor air quality (IAQ) while minimizing energy consumption and occupant comfort issues. These units are outfitted with excellent air filtration (MERV 13) by default which will be critical to ensuring clean and healthy indoor air. In addition, Zehnder America should provide a full system specification including all ducting, registers and accessories needed for the home in one package which greatly simplifies design and installation.
Note that Zehnder America should also be retained to balance and commission the system after installation. This is critical for proper operation and required for all high-performance buildings. This service will normally come standard with all Zehnder America packages but this should be verified in this case.
SYSTEM BALANCING:
Prior to occupancy, the fresh-air system should be tested and balanced to ensure good air mixing and adequate supply to all living spaces. The HRV vendor should provide this balancing as part of their services.
Ventilation Design
In addition to the modeled performance thresholds, in order to certify a building as a ‘Passive House’ building, projects would have to comply with the following design. Whether the project achieves full Passive House certifications, the following design guides are recommended for all projects:
- Total measured fresh-air ventilation supply and exhaust airflows are within 10% of each other. (Use the higher number as the basis of the percentage difference).
- All ventilation air inlets are located at least 10’ (“stretched-string distance”) from known contamination sources.
- All ventilation air inlets are located minimum 5’ from ventilation exhaust outlet (recommended 10’).
- Ventilation air comes directly from outdoors, not from adjacent dwelling units, common spaces, garages, crawlspaces, or attics.
- Outside air passes through a minimum MERV 13 filter prior to distribution, is changed at end of construction, and building is ventilated prior to occupancy.
- Outside air filter is located to facilitate regular service by the occupant and/or building superintendent.
- Air-sealed, class 1 vapor retarder shall be installed over all air-permeable insulation (such as fiberglass duct wrap) on ventilation ducts connected to outside.
- Fresh air (OA) supply to bedrooms is required in all dwelling units.
- Measured bathroom exhaust rates meets one of the following: ≥20cfm continuous or 50 cfm intermittent.
- Measured kitchen exhaust rates meets one of the following: ≥25cfm continuous, 100cfm intermittent for range hoods, or 5ACH based on kitchen volume.
- If kitchen exhaust connected to ERV/HRV, register is min. 6’ from cooktop, MERV 3 or washable mesh filter for trapping grease, and recirculation hood over range.
- Total supply and exhaust are within 10% of each other.
- Net pressure across envelope no greater than +/-5 Pascals.
Appliances & Venting
KITCHEN VENTING:
Kitchen venting should be provided at the lowest rate that satisfies regulations. For gas cooking, this flow rate will be specified by code. For electric cooking, limit exhaust hood airflow to 200-400 cfm maximum through the selection of an appropriately sized hood. The Home Ventilation Institute (HVI) specifies a minimum of 40 cfm and recommends 100 cfm per linear foot of range. For effective kitchen venting, sizing and placement of the hood can be more important than the air flow rate, as sizing and placement effect the capture efficiency of the hood. Hoods should be as low as practical, extend beyond the range by approximately six inches at the sides and be as deep as possible without interfering with use of the range.
MAKEUP AIR SYSTEMS:
In order to properly vent any exhaust air appliances (clothes dryers, kitchen hoods, etc..) in an air-tight home, a dedicated makeup air system may be necessary. This is especially true of homes with combustion appliances (e.g. wood stoves/fireplaces) located indoors. In this scenario, makeup air from an automatic makeup air fan is used to balance out the exhausted air.
Note that for most cases we do NOT recommend this strategy as it is costly, complicated, and adds considerable complexity to the envelope construction (insulation, air-sealing) and represents a significant energy penalty to heat/cool the makeup air.
Wherever possible, the use of all-electric systems should be considered, and combustion appliances should be installed only in outdoor locations (porches, decks, etc.).
Heating / Cooling of any outdoor makeup air may be needed once it enters the habitable space. Self-closing (magnetic) dampers should be included on all ducting to prevent air infiltration / exfiltration when the appliances are not in use. In order not to compromise occupant comfort when makeup air is being supplied to the home, a high output heating element will need to be sized and installed to heat the incoming volume of air to a comfortable temperature. Electro Industries makes an excellent, self-modulating makeup air system (MUAS) and corresponding makeup air heater (MUAH) which could be a good fit for this project. Please note: proper commissioning and continued maintenance of the makeup air system is critical to the safe operation of the home, particularly when combustion appliances are present.
Several things should be kept in mind when configuring such a system:
- Ensure airtightness at all envelope penetrations.
- All ducting insulated with vapor-closed insulation (min 2”) and vapor-closed tape all joints.
- Provide no more than 60% of the make-up air at base of range/oven.
- For Gas cooking, follow all local code requirements and manufacturer’s instructions.
CLOTHES DRYERS:
In place of traditional venting clothes dryers, non-venting (heat pump condensing) dryers can be used which require no venting, fans, controls, sensors, dedicated exhaust or make-up air systems. We strongly recommend utilizing non- venting appliances. The best resource for finding high-performance appliances in the US is the EnergyStar Online Product Finder. This database includes many types of appliances but in particular have several high-performance heat-pump non-venting driers which are very good solutions for most types of residential buildings.
Humidity Control
WHOLE HOUSE DEHUMIDIFICATION:
Buildings with low cooling loads can be difficult to dehumidify with efficient heat pump cooling systems. Cooling systems tend to satisfy the thermostat setting quickly before the system has had a chance to extract the moisture from the air. The cooling system then ramps down or turns off completely. In either scenario, dehumidification may be insufficient, leading to uncomfortably high humidity levels in the home.
For this reason, and because there are times when no cooling is required but dehumidification may be desired, we recommend at least planning for, if not installing, dedicated whole-house dehumidification systems. These systems can be stand-alone or integrated with the heat pump distribution system. In any case, high-efficiency systems, like those from Santa Fe, should be selected.
WHOLE HOUSE HUMIDIFICATION:
Excellent building airtightness and mechanical ventilation with heat and moisture recovery will help maintain healthy indoor relative humidity levels in the home. However, if there is a possibility that the home will be intermittently occupied, whole house humidification should be considered, as wintertime humidity levels could fall below levels that are healthy and comfortable for inhabitants and potentially damaging to finishes and furnishings. When selecting humidification systems, careful assessment of the total energy use should be part of the decision-making process. Bypass and fan-powered humidifiers add moisture to the air by passing air through a moistened filter. These systems use relatively little electrical energy to maintain comfortable relative humidity levels in the space as moisture transfer happens more or less passively. Steam humidifiers, though more effective, use considerable electrical energy, as the humidification process requires the conversion of liquid water to steam (using electricity), which is then injected into the heating airstream. For more information, see Energy Star’s Scoping Report for residential humidifiers. Energy star does not currently certify humidification equipment, but the energy analysis of the various types of humidification appliances is illuminating.
Hot Water
SANDEN SPLIT HEAT PUMP:
For hot water generation we strongly recommend utilizing a high-performance electric heat pump. For this project we recommend the SanCO2 heat pump to provide all hot water for the home. This unit has a ‘split’ system design. The heat pump is located on the exterior of the building, moving heat from the outdoors to the water tank. This leads to a very high efficiency and low resulting energy consumption. Importantly, it utilizes CO2, which has a much lower global-warming impact than typical cooling refrigerants. Globally, refrigerant leakage is one of the primary drivers of near-term warming and many groups have identified refrigerant management and low-impact refrigerant usage as a key aspect of any strategy to reduce global climate change.
For more information refer to Small Planet Supply
RHEEM PERFORMANCE PLATINUM SERIES PROTERRA HYBRID ELECTRIC WATER HEATER:
Another option is an all-in-one air source heat pump (ASHP) such as the Rheem XE80T10HS45U0. This unit uses a simple design where the heating element is mounted directly on the tank making it a bit easier to install and maintain than other ‘split’ heat-pump configurations. This unit is powered by electricity, making it cleaner and healthier than oil/gas fired options, and has a very high level of energy efficiency.
The downside to these all-in-one heat pumps (compared to the split units like the Sanden) is that they are noisier, they require a relatively large indoor area to pull heat from in order to work properly, and they cool the space around them. In most cases they cannot be installed in a tight enclosed closet without suffering performance issues. A unit such as this once could be installed in a mechanical room using the optional ducted installation in order to provide sufficient fresh air for the unit to operate, though we prefer the split heat pump from Sanden for noise, comfort and overall efficiency reasons. For details on the ducted installation refer to the manufacturer’s instructions page 12-13.
SHOWER-DRAIN HEAT RECOVERY:
In order to reduce DHW energy consumption and extend the capacity of the hot water tank, we recommend installing an in-line shower drain-water heat recovery element. This simple element has no moving parts and helps to save 15-25% of the energy from drain water which would otherwise be lost to the waste-water system. Given the modest first cost and quick payback of these systems, we strongly recommend installing a product of this sort. In this case, a vertical unit could be installed somewhere below the main bathroom shower. If a vertical unit is impractical, a horizontal unit such as the EcoDrain could be installed in the cellar. Some product options to review include:
Building Monitoring
ENVIRONMENTAL MONITORING:
There are several systems available for monitoring the temp, RH, CO2 and other environmental conditions. We strongly recommend installing a system of some form in order to successfully commission the home and correct any issues with indoor comfort over the first year. Environmental monitoring systems are relatively low cost, and we recommend 2 possible systems, the Wireless Sensor Tag by Cao Gadgets LLC, and the Netatmo weather-station. Both systems upload data to the internet over a wireless network and data can be accessed online. (Note: this requires a wireless network to be in operation at the home at all times)
The Wireless Tag system is less costly, but can not monitor CO2, and for this reason we would prefer the Netatmo system.
More information can be found at:
ENERGY MONITORING:
To really understand a home’s energy use, a branch circuit monitoring system is the way to go. Monitoring each electrical circuit, especially in the first months of a project’s operation, can help identify systems that are working incorrectly, using more energy than they should. For new construction projects, it makes sense to install a load center designed to do just that. Leviton offers a load center with integrated branch circuit monitoring that can integrate with other ‘smart’ controls (switching, dimming, etc.). Real-time and historical energy use data is available through the Leviton App.
More information can be found at: Leviton
Other options are available for integration with more typical circuit breaker panels. Systems such as the Curb energy monitor, the Emporia Vue and the eGauge provide customizable, real-time monitoring of electrical usage. The web/app-based interface displays detailed information about the home’s energy usage and can help to fine-tune energy conservation measures. More information can be found at:
