Dan, the conclusion of your link pretty well covers this subject and is consistent with our previous recommendations and how we address this:

Conclusion
The VAPHS has rapidly implemented CDC’s recommendations and has taken several steps to protect patient safety. The hospital shut down their potable water system on November 15, 2012 to initiate remediation. Meanwhile, a combination of bottled water and point-of-use filters were used for patient care needs. Superheating and hyperchlorination were performed, followed by installation of a chlorine drip to maintain the chlorine level at approximately 1-2 ppm throughout the system. Repeat sampling two weeks later showed that remediation was successful, and water usage restrictions were lifted on November 30, and the VAPHS declared the water system clear of Legionella. To date, no further LD cases have been detected. I would be happy to answer any questions the Committee may have.

Yes, the HVAC industry in Europe is much more advanced than in North America. They have strict licensing and apprenticeship requirements. Even architects have to first become an engineer before they can become an architect.

So my take away on the article still leaves me in favor of closed loop systems.
For the modest additional cost in an isolated radiant system verses the periodic testing (If at all) and the fix, it seems a better solution to isolate from the start.
What I get currently from the CDC
15% death rate should you get legionella.
The CDC fix should you be lucky enough as home owner to know what is going on with your trusty heat system;

Note the part about an already chlorinated public water source still failing to kill the legionella
Note the part about hyper chlorinating the system to address the problem.
Note the part about 160-170 degrees to kill of bacteria.

These seem like extreme things to keep up with fro the average DYI.
What % is really saved $ with an open loop system in the view of the whole building budget not using a proper boiler or isolated water heater or heat exchanger isolation. I do not think it is significant, more that open loop is viewed as an easier system to install, less cost to sell.
Just saying,
Dan

Posted By FBBP on 05 Feb 2014 11:40 AM

Posted By Zad on 05 Feb 2014 05:42 AM
FBBP, thanks for the link. I had found that site about a week ago and read all the research papers listed at the bottom of the page. None of the evidence presented pertains to open direct systems except for the obvious opinion of the website author. What is disappointing to me is that the website is clearly anti-open direct and yet all the evidence presented does not contain one shred of data supporting the idea that open direct is dangerous. There are numerous references to any given electric hot water tank having a 40% chance of being contaminated with Legionella but absolutely nothing on open direct. This site is a classic example of an opinion masquerading as a well substantiated position using totally unrelated data to support the opinion. So frustrating. At the end of the day, what I am left with is the fact that I could easily have an electric hot water tank installed in my house today without any question about safety, despite the well documented risk of Legionella exposure. If I were to ask for an open direct heating system to be installed, however, I would likely be met with stiff resistance due to completely unsubstantiated perceived risk. As a layperson to the plumbing and heating industry, this makes absolutely no sense to me. What am I missing?

Zad - I was wondering if your code is the same as Alberta's and that it prescribe a minimum run time? I think that is the key. I understand your frustration with rules with no back ground. If something is said often enough, it just gets parroted by people who have no idea of why, until it is commonly accepted as gospel.

I am close to the Alberta border in BC. What do you mean by run time? And why is this the key? Being a HVAC layperson I don't know what you mean, sorry.

Zad - The Code requires •••2.9 A means shall be provided to automatically prevent stagnation by cycling the Combination Heating System at least once every 24 hrs.•••
This prevents water from sitting in the tubing, like during the summer, where it could be colonized and then reintroduced to the potable loop.

If you are going to do open, I would make sure it circulates but for me, IF I was going to use electric water heater, I would just put in two, one for each.

Posted By sailawayrb on 05 Feb 2014 11:17 AM
Thanks Zad. Something else for you to consider…

When heat sources are combined with zoned HR distribution systems, it is possible for the heat source to short cycle when only a couple of these zones call for heat. This occurs because the rate of heat produced by the heat source may be much greater than the rate of heat used/released by these zones. Some heat sources in combination with low hydronic fluid volume HR distribution systems cannot absorb this excess heat rate without experiencing a rapid rise in temperature. This causes the heat source to reach its high temperature limit very quickly resulting in very short on times and short cycling. While electric heating elements can tolerate short cycling, gas valves, oil burners, ignition systems, and compressors will have a significantly reduced life expectancy.

So an electric hot water heater may be a better choice than a gas fired hot water heater with regard to this issue. You can also easily replace many electric hot water heaters for the cost of what a “pro” will charge you to install a gas fired boiler. So while we typically prefer/recommend boilers over most heat source options for HR applications, for a competent budgeted minded DIYer, an electric hot water heater may be a good DIY option.  As is always the case, doing a good ROI analysis for your specific situation parameters will confirm this.  Again, you have to properly determine the BTUs in order to size and access the feasibility of using the heat source being considered.

I just ran through your heat loss calculator and your radiant design calculator. Nice job with those, they are excellent and with the manual they are very easy to use. Sadly, the numbers don't work out so well for me. It just so happens that last night was -18F, a good night to remind me that it gets that cold here. I used -25 in my design parameters and the heat loss for the floor with radiant heat (I am going to use electric baseboard upstairs if all this goes through) was 52694 BTU/hour. To keep up on a night like last night for zone 1 (1060 sq ft) the supply temp would have to be 162F requiring 8 circuits on 6" spacing. Not a viable scenario. Given, I used an inside temp of 72 and it was only that cold in the dead of night, while during the day today it will get up to 5F. For zone 2 (188 sq ft at 74F - bathroom), 156F water temp on 6" spacing and 2 circuits. Basically the same for zone 3. I am not sure if I made a major mistake somewhere but this is what it came out as. Thoughts?

Posted By jim on 05 Feb 2014 11:40 AM
Maybe there's a lack of evidence on this because its not worth anybody's time to test the hypothesis that an open system breeds a Legionella when an open system doesn't have many advantages to make it worth testing that hypothesis in the first place.

And if your expecting to experience warmth in your feet in a radiant system then the system is probably being used in the wrong way.

This is exactly the type of attitude that stops learning and advancement in any field. We faced the same thing in one branch of cancer therapy where it was assumed that antioxidants would make chemotherapy less effective by blocking the pro-oxidant effect of the chemotherapeutic drug. Makes sense on first blush. However, when it was actually tested, in turned out that antioxidants potentiate the effect of the chemo and, at the same time, reduce side effects by protecting the healthy cells. Again, I go back to the well documented fact that 4 out of 10 electric hot water tanks are contaminated with legionella yet they are still considered a healthy and safe way to create DHW. It would be very interesting to me to know, based on evidence, how a well designed open system would function. I disagree that the upsides are too small to warrant use. From a cost and environmental perspective, there are significant advantages, particularly if it can be done safely. Instead of warm toes I should have said toes that are not cold. Our 110 year old place is pretty chilly at floor level in temps like we have now.

Sailawayrb,
What is your turn around time for a hydronic radiant heating design? Seeing the numbers on the calculator makes me wonder if I am barking up the wrong tree for our application. I just played around with the envelope number in the heat loss calculator and what a difference that made. Even though the house in 110 years old it is insulated (R12 batts with 1" foam board wrap) with a vapour barrier. I am going to have foam sprayed into the joist box ends and a seal coat sprayed on the ceiling in two months which will dramatically improve the tightness of the envelope. So, sailawayrb, what number would you suggest I use for the envelope parameter? This could completely change the design.

Zad, I can’t really critique your heat loss analysis without knowing the details of your building construction (e.g., ceiling/wall areas, fenestration areas, and associated R-values). However, your 52,694 BTU/hour does not throw up a red flag based on what you indicated. Your 162F supply temp does seem way high to me which makes me think that you entered something incorrectly into the HR design software. However, without seeing your inputs, I can’t really critique this either.

There is a Contact Us tab on our website. We are fully booked up for the 2014 construction season, but we have a team who would be happy to answer any questions that you may have as a courtesy. We would also be happy to look at your inputs/outputs and advise if we see anything that we suspect might be erroneous. The instructions explain how to save your inputs/outputs as a PDF file so you can send them to us.

ok, thanks. I will go through it again to check my numbers and send it on to you. I appreciate the help.

I'd guess the reason you see hard data on electric water tanks is because they are a proven and effective way to make domestic hot water. An open loop hydronic system has flaws outside of the bacterial question that make many professionals avoid them. Feel free to spend your own time and money to test the safety of a system that you shouldn't build in the first place because it has other demonstrated weaknesses.

Posted By jim on 05 Feb 2014 03:31 PM
I'd guess the reason you see hard data on electric water tanks is because they are a proven and effective way to make domestic hot water. An open loop hydronic system has flaws outside of the bacterial question that make many professionals avoid them. Feel free to spend your own time and money to test the safety of a system that you shouldn't build in the first place because it has other demonstrated weaknesses.

Please elaborate, what, aside from the microbial issue, are the proven shortcomings of a properly designed open direct system.

That information has been covered 100x on this forum. You're also asking a loaded question by saying a "properly designed" open loop. A properly designed open loop is in the same price range as "properly designed" closed loop system with fewer risks to the system and occupants. So why do you even care how an open loop performs if the closed system that eliminates risks inherent in the open design costs about the same?

Or do you want an improperly designed open loop to save money?

Ergnut, I have scoured this and other forums on this issue and from a layperson's perspective, none of the criticisms make sense. A paper in the New England Journal of Medicine was published several years ago that found that 70% of what is done in medicine has no scientific basis. 30% of medical practice has a sound basis in science and the rest is simply done because it has been done before, and on and on it goes. I can't help but wonder if this is something similar.

If a heating system provides enough water at the right temperature in a safe way, what is the big deal?

I have found not one documented case of infection associated with an open direct system.
For people that have open systems with properly sized heaters designed to cope with the cycling, their systems work very well, based on their assessment.
Users love the efficiency and cost savings.

So, please, I am not being facetious, nor do I have anything to gain from this discussion, other than information that will help me make decisions on our system.

What are the flaws you speak of? Are they evidence-based or are they opinion-based? I am honestly curious.

systems being destroyed by being connected to fresh water is a real concern. a whole developement of "open direct" systems in washington was taken out, apparently by some grounding issues that damaged the PAP tubing in the system (rated for potable). I've seen more than a couple of systems myself succumb to mineralization or other water quality issues. It's not good for most systems to be constantly introducing fresh water. Very small or very simple systems MAY be ok in some cases. but not most of the cases out there actually getting open direct systems; usually the design tradeoffs to make the systems work, IF they do, compromise the comfort and efficiency of the systems themselves... i.e. bad balancing/lesser zoning, zone by pump, large pipes, etc.

There is no significant advantage to efficiency for open direct, unless adding a heat exchanger makes you turn up your water heater temperature, and that is a VERY narrow band of potential systems indeed. the temperature drop across a heat exchanger is not a significant efficiency loss in any other case. Also, Heat exchangers can be insulated.

the ONLY significant advantage of SOME open systems is initial cost savings... and not even all systems see that. heat exchange is a one time insurance payment that protects the owners and their systems and, in some cases, their homes as well in the event of a leak, and it prevents the need to make any other real compromise in the system design to ensure safety or comfort. Going open direct results in a cascade of design decisions that simply put greatly increase the chances of system failure or underperformance.

even a cheap radiant system isn't cheap. protect it. protect you. make sure it works.

Thanks Rob, those are perspectives that I have not found in other discussions on this topic. Much appreciated.

Rob - two other points that might be worth discussing along your lines would be the need to use bronze and the fact that frost protection cannot be added.

Right, brass or stainless steel components would be required for an open system. However, closed systems that neglect to use O2 barrier PEX will have this same issue too.

Everything Rob said...just like to add: If one were to make the decision on behalf of one’s family that open direct systems are a no risk exercise; that decision is clearly based on lack of full scientific certainty and said system will ultimately be passed onto the next purchasers of the home - who may unbeknownst to the seller, be potentially vulnerable to a potential condition of the water potentially created by the system – that’s why they call it scientific uncertainty. If the sellers had explored the issue and do not provide full disclosure - it says something about character doesn’t it? If the seller does disclose then at least they correctly afford the new buyers the opportunity to satisfy for themselves whether the system is safe for their family; ergo there remains in the transaction from day one, an unanswered question about the safety of the system.

I believe Zad’s point was that many domestic hot water systems already have Legionella without their owners even knowing about it and that having an open loop HR system might be not be any worse. So I believe Zad was looking for data to substantiate this along with an approach to prevent or treat Legionella in such a system (i.e., either a domestic hot water system or an open loop HR system). Some of us have had the pleasure of installing Legionella treatment/prevention systems in domestic hot water systems in elderly care facilities and fully understand how a chlorination system can be used to accomplish this. So, from a sound scientific perspective, a proper chlorination system could likely be used for an open HR system too. However, no competent HR company would ever recommend using an open loop HR system. In most regulated states, selling a home with an open HR system without disclosing it would be misdemeanor…and likely a felony if someone were to get ill or die from using it.

Thank you sailawayrb,

Re: I believe Zad’s point was that many domestic hot water systems already have Legionella without their owners even knowing about it and that having an open loop HR system might be not be any worse.

Acknowledged. My participation in this conversation is more macro based and not so much addressing individual comments. The extent of my interest are others who might rely on the dialogue and draw conclusions that may not be in their best interest.

Re: So I believe Zad was looking for data to substantiate this along with an approach to prevent or treat Legionella in such a system (i.e., either a domestic hot water system or an open loop HR system).

Acknowledged. As discovered – it does not exist.

Re: “…Legionella treatment/prevention systems…chlorination system…”

Acknowledged. As an ASHRAE member you are likely aware of the developments with proposed Standard 188, Prevention of Legionellosis Associated with Building Water Systems - your comments are in-line with those in the document. The challenge of course is the Standard as it has been proposed, excludes single-family residential buildings and in my opinion, until mandatory testing of residential bacteria contamination control systems (chlorine, heat and 24 hour purge control) fall in line with the mandatory testing of residential chemical contamination systems (atmospheric vented back flow) they remain flawed solutions.

Re: “…no competent HR company would ever recommend using an open loop HR system.”

I agree.

Re: “…selling a home with an open HR system without disclosing it would be misdemeanor…and likely a felony if someone were to get ill or die from using it.”

I agree and thank you for stating the potential consequences for unethical behaviour.