The Ons & Offs of ERV Effectiveness
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The Ons & Offs of ERV Effectiveness
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Research identifying common issues affecting the effectiveness of Energy Recovery Ventilation in Minnesota buildings and developing a protocol to optimize their performance.
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The Ons & Offs of ERV Effectiveness
- 1. THE ONS & OFFS OF ERV EFFECTIVENESS Josh Quinnell, Ph.D. Sr. Research Engineer A Conservation Applied Research & Development Field Study
- 2. Welcome Conservation Applied Research & Development (CARD) Webinar Mary Sue Lobenstein | R&D Program Administrator marysue.Lobenstein@state.mn.us mn.gov/commerce
- 3. Minnesota Applied Research & Development Fund Purpose to help Minnesota utilities achieve 1.5 % energy savings goal by: • Identifying new technologies or strategies to maximize energy savings; • Improving effectiveness of energy conservation programs; • Documenting CO2 reductions from energy conservation programs. Minnesota Statutes §216B.241, Subd. 1e. mn.gov/commerce
- 4. CARD RFP Spending by Sector thru mid-FY2017 • 8 Funding Cycles • Nearly 380 proposals • 92 projects funded mn.gov/commerce Multi-sector (21) 25.3% Commercial (36) 37.6% Residential 1-4 unit (15) 18.7% Industrial (10) 8.6% Multifamily 5+ unit (4) 6.6% Agricultural (6) 3.1%
- 5. Pg. 5 Research Financing Policy Programs Discover + Deploy the most effective solutions for a healthy, low-carbon economy Planning & Consulting
- 6. Pg. 6 The Ons & Offs of Energy Recovery Ventilation Effectiveness PRESENTER: Josh Quinnell, Ph. D. Senior Research Engineer Center for Energy & Environment
- 7. THE ONS & OFFS OF ERV EFFECTIVENESS Josh Quinnell, Ph.D. Sr. Research Engineer A Conservation Applied Research & Development Field Study
- 8. Pg. 8 Today’s Agenda • Background • What is Air-to-Air Exhaust Energy Recovery? • Why energy recovery? • Expectations • Some people are saying “Energy Recovery doesn’t work” • What are expectations and why do “they” say this? • Methodology • Characterizing ERVs in Minnesota & in-depth study of representative units • Results • ERVs in Minnesota • Energy Savings & Performance • What types of problems impede energy recovery? • Recommendations & Conclusions • What do we do with what we have learned?
- 9. Pg. 9 Today’s Agenda • Background • Expectations • Methodology • Results • Recommendations & Conclusions
- 10. Pg. 10 Air-to-air exhaust energy recovery systems (ERVs) • ERVs transfer energy between incoming and outgoing air streams to reduce the energy to condition outside air • Energy recovery is subordinate to ventilation flow!
- 11. Pg. 11
- 12. Pg. 12 Energy recovery performance • 𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒𝑛𝑒𝑠𝑠, ε = 𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑒𝑑 𝐸𝑛𝑒𝑟𝑔𝑦 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑝𝑜𝑠𝑠𝑖𝑏𝑙𝑒 𝑒𝑛𝑒𝑟𝑔𝑦 𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑦 • Design parameter • By itself, not useful for energy savings • 𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑦 𝐸𝑛𝑒𝑟𝑔𝑦 𝑅𝑎𝑡𝑖𝑜, 𝑅𝐸𝑅 = 𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑒𝑑 𝐸𝑛𝑒𝑟𝑔𝑦 𝐸𝑛𝑒𝑟𝑔𝑦 𝑢𝑠𝑒𝑑 𝑓𝑜𝑟 𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑦 • Aligns ERVs with performance metric of heating & cooling eqpt. • Annualized value represents total energy savings • Resources: • (2016) ASHRAE HVAC Systems & Equipment Chapter 26, • (2011) AHRI Guideline V, • (2014) AHRI Guideline W
- 13. Pg. 13 ERV operation varies over the year
- 14. Pg. 14 Flow rates through ERVs • Usually rated and specified at balanced flows, but operated at unbalanced flows • When supply is greater than exhaust: The largest temperature/humidity changes occur in exhaust stream (common) • Energy savings is limited by the lower flow rate!
- 15. Pg. 15 Energy code (ASHRAE 90.1-2010 / IECC 2012) % Outdoor Air at Full Design Flow Rate Zone <30% ≥30% & <40% ≥40% & <50% ≥50% & <60% ≥60% & <70% ≥70% & <80% ≥ 80% Design Supply Fan Airflow rate (cfm) 3-5B, 3-4C NR NR NR NR NR ≥ 5000 ≥ 5000 1-2B, 5C NR NR NR ≥ 26000 ≥ 12000 ≥ 5000 ≥ 4000 6B NR ≥ 11000 ≥ 5500 ≥ 4500 ≥ 3500 ≥ 2500 ≥ 1500 1-6A NR ≥ 5500 ≥ 4500 ≥ 3500 ≥ 2000 ≥ 1000 > 0 7, 8 NR ≥ 2500 ≥ 1000 > 0 > 0 > 0 > 0 • Performance Requirement: 50% (total) effectiveness at design • Standards Evolution • 2007: 70% OA and 5,000+ cfm • 2013: 10% OA
- 16. Pg. 16 Today’s Agenda • Background • Expectations • Methodology • Results • Recommendations & Conclusions
- 17. Pg. 17 What are Energy Recovery Expectations? ¯_(ツ)_/¯¯_(ツ)_/¯
- 18. Pg. 18 What are Energy Recovery Expectations? • There are no consistent expectations. • Performance expectations? • Reduce design loads on heating & cooling systems • Decreases annual energy use to condition outside air • It works; not associated with “problems”
- 19. Pg. 19 Evidence suggests high rate of problems 63% 67% 55% 62% 31% 22% 10% 11% 6% 11% 35% 32% 0% 20% 40% 60% 80% 100% PBEEEP Call backs Engineers Owners MSC2010 Reported Issues Control Operation Design & Install
- 20. Pg. 20 Today’s Agenda • Background • Expectations • Methodology • Results • Recommendations & Conclusions
- 21. Pg. 21 Methodology Objectives: 1. Characterize ERVs in Minnesota commercial and institutional buildings 2. Detailed study of a representative sample of ERVs 3. Characterize and improve ERV performance
- 22. Pg. 22 Characterization • ERV Market Characterization Study for CenterPoint Energy (2010) • Public Buildings Enhanced Energy Efficiency Program (PBEEEP) (2012) • Limited information from rebated ERV installations (2007 – 2012) • Yielded information on 404 ERVs in Minnesota
- 23. Pg. 23 Study representative units • Pick representative units for study • Screen units for a representative sample • Find units that represent typical MN ERV specifications • Identify units that may not meet expectations (e.g. have “problems”) • Monitor them for ~6 months (heating / cooling / swing) • Setup data trending from automation systems • Install pressure, temperature, and humidity logging equipment • Conduct airflow and air leakage tests • Identify & correct issues • Monitor post-implementation performance for savings estimates
- 24. Pg. 24
- 25. Pg. 25
- 26. Pg. 26
- 27. Pg. 27 Today’s Agenda • Background • Expectations • Methodology • Results • Recommendations & Conclusions
- 28. Pg. 28 Results Institutional K-12 Schools Enthalpy Wheel* One Commercial Higher Ed. Plate Two Other Membrane Three+ 0% 20% 40% 60% 80% 100% Institutional Building Type Building Type Unit Type Units per building
- 29. Pg. 29 Sizes • Characterized units: 3,575,700 cfm of rated capacity • Units range from 215 cfm to 60,000 cfm • Lower quartile by size (<3,240 cfm) constitute 5% of total flow • Upper quartile (>11,030 cfm) constitute 63% of total flow
- 30. Pg. 30 Representative Units ERV Manufacturer Type Application Supplies Design Supply/ Exhaust Flow AHRI ε s1 AIRotor Wheel AHU AHU 5,600 /5,600 70 s2 Semco Wheel DOAS FCU 21,100 / 21,100 78 s3 AIRotor Wheel DOAS VAV 11,800 / 7,400 70 s4 Semco Wheel AHU CAV 33,600 / 33,600 78 s5 HeatXChanger Plate AHU VAV 24,000 / 17,000 44/24 (67**) s6 AIRotor Wheel RTU VAV 5,000 / 5,000 70 s7 Airxchange Wheel RTU AHU 5,600 / 5,600 66 s8 Innergy tech Wheel DOAS VAV 5,500/ 5,500(2) 71 s9 Thermotech Wheel AHU VAV 33,600 / 33,600 73***
- 31. Pg. 31 High level savings summary • Initial Conditions • 3 units were non-functional • 3 units suspected of major problems were functional • 1 unit with non-specific concerns was highly functional • 2 units without concerns were highly functional • Post-Implementation • 9 units functional • 2 units with 86% of new savings • 5 units with 14% new savings • 2 units with no new savings Total Savings Pre Post New $ 40,683 $ 57,851 $ 17,168 + 42% Savings Profile % Source 88% Gas 12% Electric
- 32. Pg. 32 Findings • 75 Issues found on 9 units over 2 seasons Perception & Expectations Energy Efficiency Minor Issues
- 33. Pg. 33 Issues by Category
- 34. Pg. 34 Energy Efficiency Issues ~1/3 (24) issues analyzed for energy penalties Suggests 50% more savings than achieved, but we can only claim savings once! Heating Penalty Heating Cost Penalty Cooling Penalty Cooling Cost Penalty therms/yr $/yr kWh/yr $/yr Min 16 13 52 6 Max 4,721 3,857 5,213 584 Average 1,388 1,134 1,498 168 Sum 27,756 22,676 23,963 2,684
- 35. Pg. 35 What are some of these issues? Tag Description Category Heating Penalty Heating Cost Penalty Therm $ s1i1 Stuck MAD Part failure 293 239 s1i2 High EAT lower limit Operator override 354 289 s1i3 High MAT lower limit Operator override 772 631 s2i1 Backward bypass control Installation issue 2,232 1,824 s2i2 Incomplete bypass sequence Control sequence 2,232 1,824 s2i3 Torn canvas Part failure 1,533 1,252 s2i4 EAT at purge Installation issue 240 196 s2i5 Miswired wheel speed control Installation issue 2,177 1,779 s2i6 No heat valve and wheel staging Installation issue 1,742 1,423 s4i1 Discharge 10F below DAT Setpoint 2,869 2,344 s5i1 Reverse damper polarity Operator override 4,721 3,857 s5i2 High EAT lower limit Operator override 4,721 3,857 s5i4 High EAT lower limit Setpoint 167 136 s5i5 Warm up schedule Scheduling 425 347 s6i2 Failed wheel VFD Part failure 2,452 2,003
- 36. Pg. 36 Performance Expectations • When does energy recovery occur? • 60% to 80% of recovery between 0ᵒF and 45ᵒF • <10% of recovery below -5ᵒF or above 85ᵒF • Little recovery between 45ᵒF and 65ᵒF
- 37. Pg. 37 Performance Expectations • What does energy recovery do? • Ventilation savings in line with claims • Primarily reduces heating energy for outside air • Reduces peak cooling load; downsize cooling to leverage
- 38. Pg. 38 Today’s Agenda • Background • Expectations • Methodology • Results • Recommendations & Conclusions
- 39. Pg. 39 If there were Performance Expectations Most ERVs in this study would not meet them! • Units are specified at full capacity and balanced flows • Exhaust flows are less than supply flows due to point exhaust systems and other AHUs • Effectiveness increases; energy recovery decreases • As-operated flows are different (usually less) than design (~30% less in this study!) • Fixed capacity ERVs are installed in variable capacity systems • ERVs in mixed air units only see fraction of typical capacity (outside air flow rate fraction) • Retrofits cause system-wide airflow and building pressure changes
- 40. Pg. 40 Barriers to peak performance • Lack of familiarity among staff that touch systems • Technicians & operators rightly/wrongly have learned from experience • This is a major barrier when this experience is from poorly or oddly implemented energy recovery • No continuous feedback that they are working • Blinking BAS graphics do not count! • HVAC systems pick up the slack • Hard and rare to measure performance • Problems/behaviors persist; they are normalized
- 41. Pg. 41 Good News – It’s easy to validate Energy Recovery • Little reason to doubt AHRI rated effectiveness • Let’s not waste effort validating HX performance • Validating an ERV does not require Rcx effort • ERVs on/off at the right times are working! • Caveat: Flow rates are understood (IAQ, building pressure) • Energy penalties are avoided if staff • 1) Identify when an ERV should be running and • 2) Assess whether an ERV is running
- 42. Pg. 42 Validating working ERVs
- 43. Pg. 43
- 44. Pg. 44 General commissioning guidelines 1. Large ERV systems (10,000 cfm+) must be fully- commissioned 2. Validated as-operated flows against design flows 3. Control sequences should follow manufacturer recommendations, deviations must be justified by project engineers 4. Control intent and detailed sequences should be specified and as-implemented sequences verified by an accountable party 5. Cx. agents should set operator expectations
- 45. Pg. 45 Targeted Recommendations • Design Engineers • Provide more rigorous specifications WRT control of ERVs • Mechanical and Controls Contractors • Follow engineer specifications and • Hold engineers accountable for complete specification, • Not responsible for making engineering decisions • Commissioning Agents • Ensure knowledge transfer on system intent (including control) • Validate sequencing • Document as-operated conditions where different than design • Building Owners / Representatives • Provide resources for staff to understand systems they administer • Establish expectations of semi-annual operational checks on ERV systems
- 46. Pg. 46 Conclusions • ERVs meet their AHRI rated performance • A cost effective addition to all large ventilation systems • 30% - 90% reduction in heating ventilation load • 20% - 40% reduction in peak cooling load; equipment downsizing • Energy recovery typically hindered by practical issues that occur during installation or operation • Non-functional ERVs go unnoticed • Staff are not familiar with ERV systems • ERVs don’t meet expectations due to a large variety of non energy issues • Rarely performance related issues • Identifying and resolving specific ERV issues may be time- intensive, but validating a working ERV is easy • ERV issues are avoided by commissioning and training
- 47. Pg. 47 Audience Question & Answer
- 48. CARD Project Resources CARD Web Page (https://mn.gov/commerce/industries/energy/utilities/cip/applied-research-development/) mn.gov/commerce For Reports use CARD Search Quick Link For Webinars use CARD Webinars & Videos Quick Link Links to ERV Reports: Final Report Validation Guide Operations Guide
- 49. Thanks for Participating! Upcoming CARD Webinars: • July 12: Small Embedded Data Center Program Pilot • July 26: Statewide Commercial Behavior Segmentation & Potential • August 17: Expanding New Construction Design Assistance Statewide If you have questions or feedback on the CARD program contact: Mary Sue Lobenstein marysue.Lobenstein@state.mn.us 651-539-1872 mn.gov/commerce
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- 51. Pg. 51
- 52. Pg. 52
- 53. Josh Quinnell Ph. D. | Principal Investigator jquinnell@mncee.org
Editor's Notes
- Bridget = Beginning to Lending Center & Policy section Judy = Lending Center through the IX
- Welcome to this Conservation Applied Research and Development (CARD) Webinar. I am Mary Sue Lobenstein, the R&D Program Administrator at the Minnesota Department of Commerce, Division of Energy Resources. This webinar is one in an ongoing series designed to summarize the results from research projects funded by Minnesota’s Applied Research and Development Fund.
- The Applied Research and Development Fund was established in the Next Generation Energy Act of 2007. Its purpose is to help Minnesota utilities achieve their 1.5% energy savings goal by: Identifying new technologies or strategies to maximize energy savings; Improving the effectiveness of energy conservation programs; and Documenting CO2 reductions from energy conservation programs.
- $2.6 million of this fund is set aside annually for the CARD program which awards research grants in a competitive Request for Proposal (RFP) process. Since the legislation was enacted, the CARD program has: Had 8 funding cycles, with 22 RFPs posted; Received nearly 380 proposals; and Funded 92 research projects, representing over $21 million in research dollars. As you can see by the pie chart, projects funded to date have been in all building sectors. The subject of today’s webinar is a field study which characterized representative energy recovery ventilation systems in Minnesota commercial and institutional buildings and identified common problems. It’s presented by Josh Quinnell of the Center for Energy and Environment.
- Bridget = Beginning to Lending Center & Policy section Judy = Lending Center through the IX
- Ok, I have a lot to cover here today and I am going to move through material sort of quick to facilitate that. But I am going to try to take you all with me by giving a very practical background to C&I energy recovery. Then I’m going to touch on expectations for ERV performance, which turns out to be a really interesting topic, next I’ll be as brief as possible in describing everyone’s favorite section, the methodology for this study. I’ll be spending most of the time talking about our results and all the things we learned in this study. Lastly I’ll try to boil down everything into a few recommendations, and then I’ll hit you again with what I think are the most important points I brought here today.
- Background
- Buildings ERV means a-2-a exhaust energy recovery Buildings need fresh air, consequently use energy to heat, cool, dehumid fresh air ERVs reduce that energy be using ehxuast air flows. They transer energy between air streams to reduce heating, cooling energy ERVs act on ventilation air, they don’t heat or cool buildings, consequently they are subordinate to ventilation air requirements
- This is what they look like. On the left, isolated units from product literature. Top right total enthalpy wheels Bottom right, membrane plate and flat plate heat exchanger
- Energy performance 2 metrics Effectiveness usually the only one you hear about, ratio of recovered energy to maximum. The highest value is 1, but always less in practice. Today around 0.65 to 0.8 for most units Design parameter, by itself, doesn’t communicate energy savings (btus) need a lot of other information for that RER, another ratio recovered energy to energy used. Ervs use energy to spin wheels and push air across pressure drop Aligned with heating and cooling performance metrics, compare to efficiency and energy efficiency ratio Because it has units of other metrics, you can get an idea of every savings from an annualized value That’s all I’m going to say about that, other than if you want to be an ERV master, the documentation is available Resources: 100 pages of technical material. You will understand ERVs and all of the technical nuances that I address here.
- What does an ERV do? Well, it turns out a lot of things. I like this chart to explain them, it shows the whole year using outside air temperature, and the vertical axis is how much energy recovery, 0 to 100 or somewhere in between Lets start with cooling, outside > building, we use exhaust to cool outside air and reduce load on cooling systems. Runs 100% Mild cooling, but now outside < building, we need to use that fresh air directly to do. In fact if we use energy recovery we reduce free cooling. ERVs don’t run in economizer mode Mild heating, this is where our MN ervs start to shine. Outside < building, so we transfer energy from exhaust to warm up OA. Turns out they are really good at this, at mild temperatures, ERVs can typically meet the heating load alone, in fact unless they are modulated to less than 100% they can overheat the building (exceed discharge air temperature). Modulation is key Once we get MN cold, ERVs can’t heat air alone. They slowly ramp up to 100%, then we need to use heating energy to heat outside air. In both full heating and full cooling modes, ERVs are like the first stage, they meet part of the load, then the hvac does the rest Once we get to iconic MN cold, we run into another issue. ERVs are too effective. But instead of heating up too much, they cool exhaust air too much. This results in potential condensation and subsequent freezing. This can block airflow and cause some other problems. It is commonly avoided by reducing the amount of recovery. ERV has to do all those things, coordinate several control sequences, with other pieces of equipment. Frankly, it is pretty complicated. Perhaps this gives us insight into how ERVs might be perceived if any one of these steps goes wrong. Its really easy to forget one, so I’m going to go over them slow. ERVs heat and cool ventilation air by exhaging energy with exhaust air. These activities are represented by red and blue here. Lets start on the far right. Cooling. When the outside conditions are higher than the return conditions. ERVs recovery energy in cooling mode. In this case some temperature and usually humidity pass from the outside air to the exhaust air. That energy is dumped out of the building and less energy is needed by the cooling system to meet the discharge conditions. When temperatures go mild, buildings go into economizer mode to get free cooling. In this case since the outside air is colder than the building air we don’t want to recover energy so we turn ERVs off. If we left it on our economizer wouldn’t work as well, we would slow down cooling to the building. OK so below economizer operation we enter heating season. This is where ERVs really shine. It turns out that at mild outside air temperatures, say between about 32 and 50F, an ERV can recover so much energy from the exhaust flow, it can overheat the space. To prevent this, ERVs often modulate down. They recover less energy than they can so that the discharge air can remain on target. Usually during these temperatures, heating energy isn’t even necessary for ventilation air. The entire load is met by the ERV. But when it starts to get colder, the ERV will go into maximum recovery. It’s doing its job at these very cold temperatures, but it usually isn’t enough so the ERV preheats most of the outside air and then the heating system finishes it off to get to the proper discharge. When it gets very cold, like bone-chillingly cold, ERVs again are “too good.” In this case, they transfer so much energy that the exhaust air temperature can fall below the freezing point. In that case it can start to snow in the ERV or ice can build up. To prevent or minimize damage from this, ERVs are often ramped down to again only partial recovery. So depending on the time of the year an ERV can be subject to about 5 discrete operations. It has to do them all for maximum energy savings.
- A special note about flow rates Specified and rated at balanced flows; operated at unbalanced flows Relative sizes of supply and exhaust 1000 cfm / 1000 cfm balance. 1000 cfm, 900 cfm Common situation in building is that supply is greater than exhaust. Think about it an air handler pulls in some supply air. You’d like to get all the exhaust air back, but you have toilet and kitchen exhausts, so it doesn’t make it back. You get unbalanced flow. If you return only 900 cfm from your 1000, you’re energy recovery is going to be reduced by about 10% compared to your design
- We have a few energy codes, updated in 2015, they both say the same thing on energy recovery. For our climates, big systems need energy recovery, especially if they have a lot of outside air. You can dodge ERV requirements below 30% OA, but this probably isn’t a cost effective solution. The code guys know this, the 2013 version says systems down to 10% OA need energy recovery, this is going to be virtually every system. They are super aggressive about this because of what I just said, energy recovery is cost effective, often from day one via lower first costs. There is also a performance requirement. Energy recovery systems essentially need 50% effectiveness at design conditions. We’ll ignore that for now, any sensible design and installation should achieve that value. 2007 req. 2010 req. (current energy code) 2013 req. ERVS req. for OA @ >20%
- Alright. I walked us through energy recovery hopefully just enough to fill in the gaps some of you may have had, now I want to shift and talk about our study. Our study is predicated on field evidence that “ERVs are not living up to expectations” Not living up to expectaitons. Ok, that is an easy thing to say, but what does it mean?
- So what are some expectations? It works. Yep. That’s great. Its not wrong, in fact its pretty important, but it doesn’t tell us much. Of course, we expect things to work (can we agree on what work means?) It saves energy reduces costs. Ok. That’s good right there, adding a little more specificity. It has to work and save. Is anyone out there measuring ERV energy or cost savings? If they aren’t, is it possible for an ERV to miss our expectations? How would we even know? Ok. Engineer hat on. This engineer. She reads ASHRAE. She knows AHRI. She specifies HVAC systems with ERVs and leverages them to reduce cooling system size. This is a good expectation. IF an ERV doesn’t reduce the cooling load by the amount she thought, that building can’t get cool. That will be noticed. That ERV didn’t live up to its expectation. Lastly, heres my guess. Basically the same as #2, but I’m a little more specific. I know its about outside air. But again, I run into this big problem. Am I measureing anything to make sure this happens? How do I know? Ok. I’m throwing my hands up again. It isn’t clear that any of these answers help me explain how ERVs might be missing expectations. What does field work say? Why aren’t ERVs living up to expectations?
- So what are some expectations? It works. Yep. That’s great. Its not wrong, in fact its pretty important, but it doesn’t tell us much. Of course, we expect things to work (can we agree on what work means?) It saves energy reduces costs. Ok. That’s good right there, adding a little more specificity. It has to work and save. Is anyone out there measuring ERV energy or cost savings? If they aren’t, is it possible for an ERV to miss our expectations? How would we even know? Ok. Engineer hat on. This engineer. She reads ASHRAE. She knows AHRI. She specifies HVAC systems with ERVs and leverages them to reduce cooling system size. This is a good expectation. IF an ERV doesn’t reduce the cooling load by the amount she thought, that building can’t get cool. That will be noticed. That ERV didn’t live up to its expectation. Lastly, heres my guess. Basically the same as #2, but I’m a little more specific. I know its about outside air. But again, I run into this big problem. Am I measureing anything to make sure this happens? How do I know? Ok. I’m throwing my hands up again. It isn’t clear that any of these answers help me explain how ERVs might be missing expectations. What does field work say? Why aren’t ERVs living up to expectations?
- Very limited field evidence does suggest that there are a lot of problems associated with ERV systems We still have to use air quotes around “Problems” because it probably means different things to different folks. Nonetheless, we have some prior work comprised of interviews with different groups and Rcx summaries that reports on problems These different groups report problems that we have done our best to lump together. We see high rates of problems associated with controls, we see issues that manifest during the operation of the units, and some issues that are associated with the design and installation. So we can’t really back much out from this, what we can do however is set the stage for our work. Specifically, what problems are these groups referring to? What are the energy savings consequences? Does energy recovery live up to its potential? The purpose of this study is answer these questions The answer of course is “problems.” This isn’t specific, or necessarily right, but were getitng some where. People working in and around ERV systems report “problems,” at a pretty high rate too. Various groups report the same types of problems at similar rates. Control problems are frequent. This is data from 2010 study by the way. Problems come up during the operation of system. Sometimes there are more fundamental problems with the design and installation of the system.
- Ok. Very high level methodology. Lets roll through this.
- Approximately described in 3 steps. We need to figure out where energy recovery is implemented, figure out the demographics of C&I energy recovery in Minnesota. This will help inform our study. It will give us a baseline for what we are looking for. As that is established, we need to pick representative units to study. We’re interested in ERVs that are both similar to those found in MN and similar to those that “are not living up to expectations,” We study those ERVs in detail, Find their problems, fix their problems and then measure savings.
- We had access to three data sources, from which we obtained some information about 404 ERVs in Minnesota. We used this information to find out typical types, sizes, ages, manufacturers, rated performance.
- Pick units to study We screened a bunch of units to find ones that match our characteristics, size, type, mfg, We want to find units that have problems, they aren’t meeting someone’s expectations After selecting those units we setup to monitor them to find out how they are working heat/cold/swing Trend BAS data Install logging equipment Do short term characterization Then we present our findings and fix issues We continue our monitoring to measure performance, validate savings, and maybe set some performance expectations for working ERVs
- ~60 ERVs screened RTUs, giant air handlers, tiny specialty units.
- Instrumented the 9 ERVs with pressure, T, RH logging equipment. In addition gathered whatever trend data available. Co-located with BAS measurements (where available) On site remote data collection
- Short term air leakage and air flow measurements. As well as outlet distribution characterization. That was fun on the roof during the winter, especially with freezing rain.
- Ok the best part. We learned so much in this study.
- A few headline characterizations. First, we found that typically multiple ERVs per building Enthalpy wheels dominate units in MN. About 80% of ERVs are spinning total enthalpy wheels. To a lesser extent we find fixed plate (temperature only ) heat exchangers. And an even smaller extent membrane plates. I think there are several other ERV types listed by ASHRAE, heat pumps, run around loops. Zero of them were documented in this phase of the project. ERVs are found most frequently in institutional buildings about 70%. Commecial buildings tend to have high OA, auto shops, casinos, gyms, fitness centers. Of those institutional buildings we have K-12 schools and higher-ed buildings. Then a mishmash of all other types of municipal and state buildings.
- The ERVs in our data set comprise 3.6 million CFM. They range in size from 215 to 60,000 cfm Lower quartile (25% of units under 3240 cfm are only 5% of total flow) Upper quartile (25% of units above 11,030 cfm are 63% of the flow) Hugely important fact, big ERVs dominate total savings potential. We should focus on big units. Big ERVs are more than 10 times important than small ERVs
- We represented units from 6 manufacturers. 8 enthalpy wheels and 1 flat plate heat exchanger. Central air handlers, outside air systems, RTUs Supplied air to air handlers, fan coil units VAV systems, CAV systems, These units were 5000 cfm to 33,6000 cfm. They generally had high effectiveness, 10 to 20% higher than TRM default.
- High level summary. 9 units initially saving 41k/yr, left them saving 58k/yr. Over 17k in new savings, or about 40% increase Almost 90% gas savings, we did find electric savings, but this is against a generic cooling system. Actual savings are diminished by better cooling system performance On a unit basis
- Well, we report 75 issues on the 9 units over 2 seasons. They were fairly evenly split into three groups. We had a first group that had energy consequences. These issues cost energy and money. We had another third that were minor issues. This is where we report dirty air filters. Lastly, we have a group of problems we that affect the perception and expectations of staff. These don’t necessary have energy consequences, other than they cause staff to lose confidence in the systems. It turns out, we find a lot of issues that don’t have energy consequences, but are still problems that frustrate staff. Clearly there is a huge opportunity here. We’re fortunate that so many of our problems ~66% aren’t performance related. But they do, indirectly. These are the kinds of problems that make it difficult to implement advanced energy savings measures.
- If we break out these issues by categories we get this. 11 different categories. We have general control sequence issues. We have neglected maintenance (dirty air filters) We have installation mistakes We have communication problems, for example BAS displays, or sensor issues We found broken sensors We found failed parts (vfd, actuator) We found overly conservative set points We found operator overrides. Often set points set to insane values. In some cases there were funamental design issues A good number of these units operated at below their design figures. Lastly, we had typical scheduling problems. Whew, that is a lot of problems. Looking at the group we checked for energy issues, what do we get?
- Well, all over the map. All these issues combined were estimated to be about $23K in heating and 2.7k in cooling. IF you were paying attention, you’ll note this is about 50% more than we reported saving. That’s because some sites had multiple overlapping problems and we can only get the savings once if we fix both issues. Contrary to our expectations, suboptimal economizer and frost control settings were not very impactful dollar or energy wise. So what was?
- Lots of various things, note here we have many installtion mistakes and operator overrides were costly. These things typically fully disabled recovery.
- I mentioned before that we might not have consistent expectations for ERVs. Lets use our 9 instrumented ERVs to set some expectations! Plot description. Heating domination Ultra cold / ultra hot is minor Mild weather, flat because loads are low and economizer
- What do ERVs do for our ventilation load? Plot Heating wow 30 to 90%; ERVs in MN primarily reduce the load to heat outside air Cooling, smaller 10 to 25%, but peak is 20 – 40% yielding opportunity to downsize cooling systems
- It’s patently obvious that a few of the units in this study were never sincerely commissioned and were avoided during recommissioning efforts. 50% of the found savings in this study would have been uncovered during initial Cx work. The remaining during routine Rcx work. Staff can’t be afraid to Rcx an ERV. That said, Rcxing an ERV is not necessarily a straight forward thing. Every single unit (including some ostensibly similar units at the same buildings) were implemented differently. Different jargon, control settings, etc.
- Mature components, we seldomly doubt the effectiveness of heating & cooling coils. Well the same is essentially true for an erv. Problems don’t occur with the passive component, they occur with its installation, programming, and operation. Sure, like a HVAC system a component might be designed or sized poorly. But this is rare
- Thank you for attending this CARD webinar. You can download the final report on this project from the direct link on this slide. There are also links to two other related ERV guides that CEE created as part of this project. The link for the CARD web page is also on this slide. The web page has various resources and information related to the CARD program and to CARD research projects, including links to this and other recorded CARD webinars and final reports. Use the quick links indicated to help you navigate to what you are looking for.
- Thanks again for participating today! Before we leave, I want to take this opportunity to mention a couple of upcoming CARD webinars that might also interest you: July 12 – CEE and Wisconsin Energy Conservation Corporation will conduct a webinar on the Small Embedded Data Center Program Pilot July 26 – Illume Advising will conduct a webinar on the Statewide Commercial Behavior Segmentation and Potential project August 17 – The Weidt Group will conduct a webinar on a pilot program which investigated an option for Expanding Utility New Construction Design Assistance Programs Statewide Please contact me if you want more information on how to sign up for any of these webinars or if you have questions or feedback on the CARD program.
- That’s about it. Thanks for your time and listening in with me today. Before I quit here, I’d like to acknowledge my colleagues Ben Schoenbauer and Dave Bohac who put in equal time on this project. I’d also like to thank Mary Sue at commerce for helping us restructure this project to incorporate the pilot, that really expanded the utility of this work. I’m happy to take questions if we still have time. I’m also available offline to talk about the project, either what you saw or some of the material I didn’t present.