EEBA Newsletter

The views expressed in these articles are solely those of the author and do not reflect the views of EEBA staff, officers, or board members. EEBA welcomes guest articles from qualified authors, and we offer these articles as a service to the high-performance housing industry as a way to encourage discussion and collaboration between industry professionals on relevant issues.

Posts From April, 2019

HERS Raters: An Untapped Resource

These professionals can help with a lot more than inspections, but few builders understand that fact.
HERS Raters: An Untapped Resource

by Steve Byers

According to RESNET, just 20% of new single-family homes have a HERS rater involved.  When you consider that a rating is the most accurate way to gauge home performance, it's obvious that the industry has a long way to go.

Even those builders who regularly contract with HERS raters seldom take advantage of the full value these industry pros can provide.  That's unfortunate.  The best raters offer more than code or program compliance: they're extremely cost-effective quality assurance partners.  They can even help reduce a builder's liability for health and comfort issues, something today's overworked site supervisors seldom have time for.

As CEO of a building consulting and training company with more than 25 years in the home performance business, I find that builders are more willing to take advantage of a performance-focused rater's services if they better understand how we work.  The relationship is more like that with the architect or engineer than with the plumber.

What Raters Do

The most obvious job of a rater is to produce the HERS index score.  A good enough score will demonstrate energy code compliance and can qualify the home for certification from programs like ENERGY STAR, Zero Energy Ready and LEED.

However, the HERS Index is the cherry on top of our work, not the work itself.  When done properly, the rating process serves an important quality control (QC) function.  For instance, if the home doesn't pass the blower door test, the rater can tell the builder where the air leaks are.

But QC is just the minimum we offer.  Builders who want to leverage their rater's skills will make them part of the quality assurance (QA) program.  The difference here is one of depth: while QC is a simple and straightforward pass/fail test, a rater who offers QA will find the underlying reasons behind that air leakage (or any other performance-related issue), suggest approaches for doing better next time, and train the builder's team on those approaches.

The most effective QA starts at the design stage.  A performance-focused rater can look at a set of plans and see what's going to be difficult to get right in the field.  For instance, the rater might spot areas in a complicated roof design that will be a challenge to insulate and air seal.  The rater might work with the architect to determine the best locations for duct chases.

A good HERS rating organization will also likely have additional value-added services they can offer to builder clients.  For instance, my company does HVAC Design and performance services like airflow balancing.  We can train the builder's sub-contractors in high-performance building.  We have even offered builder clients post-closing walkthroughs to train homeowners on performance issues like how to use the smart thermostat as well as how and when to change the furnace filter.

These quality control steps are above and beyond what most project superintendents have time to provide.  When made part of the schedule for every home, they play an important role in lowering the builder's risk exposure.

Finding a Rater

Of course, builders who want to tap into the full potential of a performance-focused HERS Rater will have to find one first.  As with any trade or profession, quality and competence vary widely from company to company.

A good start is the RESNET Rater Registry (http://www.resnet.us/directory/search), which lets anyone find HERS Raters in their area.  However, it doesn't tell you how good each rater is.

Fortunately, every HERS Rater operates under the oversight of a HERS Provider, which performs periodic QA on the rater's work.  The builder should ask the Provider about any issues, past or present, with a particular HERS Rater they are considering.

Things to ask the rater directly include their pricing, what valued added services they offer, what trainings they have attended, how long they have been in business and how many homes they have rated.  And of course, get—and actually call— a few builder references.  Production builders should also ask the rater about their capacity and determine if they can keep up with the builder's volume.

It's a good idea to go to the ENERGY STAR website to see if the rater is qualified to deliver certification (https://www.energystar.gov/index.cfm?fuseaction=new_homes_partners.locator&s=mega).  Even if you don't need this, it's a useful filter—ENERGY STAR sets a relatively low bar for raters, so I would be suspect of a rater who hasn't at least made that effort.

You should also look for signs that they stay current with industry trends and practices.  Do they belong to the local HBA?  Do they participate in ongoing training events like the annual EEBA Summit?  For instance, my company and others have formed a collaborative, Energy Professional Exchange (https://energyproexchange.com/) to advance the level of professionalism and performance in the rating industry.

Time invested in finding a good, performance-focused rater pays real dividends.  This pro can help you solve problems, put more effective construction details in place and, ultimately, build better homes for your customers.  It could be the best business relationship you never thought about.

Steve Byers is CEO of EnergyLogic, Inc., a building performance consulting company in Berthoud, Colorado.

The Problem with HRVs

When integrated with the HVAC system, most E/HRV's don't deliver the desired ventilation air. A new design seeks to solve this problem, but we need your input.
The Problem with HRVs
by Srikanth Puttagunta, PE
 

Builders believe that if they install an Energy Recovery or Heat Recovery Ventilator (E/HRV) they have ensured good indoor air quality. In reality, that's seldom the case.

To deliver the needed fresh air, an E/HRV must be installed in a way that guarantees balanced airflows—where the intake and exhaust airstreams move equal volumes. But the design of these units makes proper installation difficult and, when integrated with the HVAC system (as most are), almost ensures that they fail to work as advertised.

Of course, an E/HRV costs more than other ventilation strategies, so if it doesn't do what it's intended to, the builder has wasted that extra money.

Steven Winter Associates is collaborating with a major manufacturer to develop an ERV that solves the shortcomings of conventional units. We have completed the second prototype. We hope to have a final design by Fall of 2019 with commercial availability sometime in 2020.

Before moving to the final design, however, we would like input from the EEBA audience to make sure the product will meet your needs. We have included a link to a short survey at the end of this article.

The three major issues that lead to unbalanced airflow with today's E/HRV's are:

1. Typical duct configurations

2. The frost prevention controls they use

3. Installs that make them difficult to properly maintain

Duct Issues

Let’s start with typical duct configurations.

If the E/HRV's intake and exhaust ducts aren't similar lengths with the same number of bends, their resistance to airflow will vary, throwing the unit out of balance. To compensate, some manufacturers provide static pressure taps that let the installer adjust the unit's fans during installation. That compensation might be sufficient for an E/HRV that has its own ductwork, but it won't be for the majority that are integrated with the HVAC system's air handler unit (AHU). The following two scenarios explain why.

Scenario 1. Here, the E/HRV pulls stale air from the return duct, then delivers tempered outdoor air further downstream in the same duct, closer to the AHU. For this to work, the E/HRV needs to run in sync with the AHU fan. However, this also results in unbalanced air flow, as the larger AHU fan will impact the smaller E/HRV fans. In this case, result will be more supply than exhaust air.

The unit could be adjusted at startup to compensate for this imbalance (though we don’t commonly see this in the field). The problem is that most of today's AHUs have two-stage or variable-speed fans, so the E/HRV can only be balanced under one of those fan speed conditions.

Scenario 2. Here, the E/HRV pulls stale air from the return ductwork and delivers tempered outdoor air to the AHU's supply ductwork. While manufacturers recommend the AHU fan run in unison with the E/HRV, most don't require it and with the AHU off, the unit may end up ventilating the AHU but not the rest of the home.

Frost Prevention

Next, let’s look at cold climate frost prevention controls.

When the outdoor air falls below a certain temperature (which varies with the E/HRV model), the core will be at risk of freezing. Manufacturers prevent this in a variety of ways, none of which are ideal.

  • On/off cycling. When temperatures fall below the frost threshold, the unit switches off for a set period of time (in really cold conditions, this could be 20 minutes or so each hour) to give the core a chance to warm up.
  • Air recirculation. Here, the outdoor intake and exhaust ports are closed, and indoor air redirected through the core's outdoor air pathway to warm it up. During this period, no whole-house ventilation is provided.
  • Exhaust only. Some units run in exhaust-only for a period of time allowing the core to warm back up. During this period make-up air will be supplied through leaks in the building envelope.
 

In each case, the home has poor or no ventilation during frost prevention. Alternatively, an electric resistance pre-heater can be installed in the outdoor air duct to prevent frost from forming in the core. This maintains continuous airflow but is energy intensive.

Install Errors

A proper E/HRV installation leaves enough space around the unit for regular maintenance, which includes periodically changing the air filters and removing the core for cleaning. Based on what we see in the field, I wonder how many builders and installers understand this. Many installations make it difficult to access the filter and core, while in other cases access is blocked by ductwork and plumbing that was installed later.

You would also assume installers know how to connect the ducts, but I've seen a lot of problems here as well, including supply and exhaust ducts hooked up to the wrong sides of the E/HRV. I also see a lot of flex duct that's not pulled tight, creating static pressures that can severely restrict airflow through either side of the unit or both.

Our Solution

With support from the DOE's Building America program and industry partners, Steven Winter Associates is developing an integrated ERV that will make balanced ventilation easier in homes. Our design includes the following improvements.

1. Simplified installation through a better form factor.

The unit will connect directly to the return side of an air handler and will pull stale air from the air handler's return ductwork. Not only does this avoid the drawbacks of each configuration type, but the fact that the ERV unit only needs two duct connections rather than four makes proper installation easier.

The unit is sized for mechanical rooms with standard ceiling heights. For an up-flow configuration, the total combined height of the ventilation unit, the air handler, and a standard supply plenum will be less than 8 feet. Maintenance access for the core and filters is also from the front, so it matches the service area required for the AHU.

2. Fans that ensure balanced ventilation under constantly varying conditions (varying AHU fan speeds, outdoor winds and indoor pressure changes, for example).

We are incorporating ECM fans. Nothing new here, right? A lot of E/HRVs have ECM fans. But rather than the typical constant torque ECM fan we are using constant flow fans, which will maintain roughly a ± 5cfm airflow range. This also allows the unit to be configured with MERV 13+ filtration.

3. Better frost prevention

The system is designed to maintain balanced whole-house ventilation during the frost prevention cycle without using electric resistance pre-heat. It does this by using a modulating damper to mix a small amount of air from the AHU supply duct with the outdoor air to pre-temper it above the core's frost point. Overall airflow through the outdoor air pathway of the core is increased, but the portion of outdoor air to exhaust air remains balanced.

Have I piqued your interest? Then take a look at the drawing.

As we continue to make refinements to the components and controls, we hope you will assist us with some feedback. This will help us ensure that the final product truly meets the industry's needs. We have posted a short questionnaire online that will help us better understand your approach to whole-house ventilation as well as what features we need to prioritize.

The survey takes five minutes or less and can be completed anonymously. We thank you for your interest and look forward to hearing from you.

Srikanth Puttagunta, PE, is a Principal Mechanical Engineer with Steven Winter Associates, Inc.