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Why not to use water heaters
zeke
Member Posts: 223
All the data I have seen say they are dead by 140 deg.
Where did you get that hospital data?
Where did you get that hospital data?
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Comments
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Siggy's article in this months PM got me to thinking. Why don't we educate the general public better? Which is why I would like to dedicate a page on my web site to why pros don't do things a certain way.
A few topics I want to cover are:
Water heaters used as boilers
Plate-less staple up
Tankless water heaters used as boilers
Would you guys be willing to help me to compile a list of cons to these methods?0 -
Sure we would...
Let's get a list started!0 -
Thanks! I'll post my argument soon... Mainly I am going to focus on efficiency and reliability. I know some of you guys have great info on health factors as well that could be helpful.0 -
Having used water heaters......
......in the past (and probably, future), I'm interested in your views, Josh.
hb
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I think there is a time and place for a water heater in heating. However I am trying to combat the internet and low ball contractors selling them for installs on homes over 1000 square feet.
Basically I want my customers to know what they are buying. In a nut shell, why boilers are 4 times more than water heaters0 -
and when that 4 times more is in their best interest!0 -
One thing I don't have is a digram showing AFUE of water heaters for specific temps and Delta T. Anybody have some info?
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Define water heater
Actually, performance and operating cost wise I'd put a Polaris or any condensing tank styled WH up against any copper, steel or cast 80% boilers in a low temperature radiant application.
Small electric tank WHs'can often outperform an oversized short cycling, mis applied (non condensing boiler in a low temperature installation)boiler also.
The devil is in the detail.
hot rod
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Well for this case lets say "conventional." Meaning atmospheric gas or electric element.0 -
I used to heat my home with a water heater...
and not just ANY water heater. I modified this water heater to allow me the opportunity to do a complete and full outdoor reset on it. I installed a normally closed solenoid on the main burner pipe between the snap acting gas valve and the burner. I figured that as long as I was going to be using the least efficient method of heating water, for the sake of learning something, the least I could do was make it as efficient as I possibly could.
It used to irk the living crap out of me to hear that heater burner running when I knew that the actual load was so insignificant. Kinda like driving a truck on flat ground with the clutch slipping. Drove me nuts.
Eventually, I installed a mod con boiler, and reduced my energy consumption by 30%. For me and my money, that in and of itself was justification enough to warrant additional cost, even though the mod con was a freebie prototype from HTP.
As HB says, "it's not so much a matter of you got what you paid for, as it is a matter of you didn't get what you didn't pay for..."
Efficiency has a price tag.
As for combination open loop/space heating water heaters, my position is well documented. Soon, it will be illegal.
ME0 -
So what's more important to you?
Working or losing a sale because of lofty ideals? My kids are expensive. If you had to do an open system to compete or lose the sale, what to do?
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Refuse to compete with "open systems".
Refuse the job, flat out!
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Amen to that! I refuse the job once or twice a week.0 -
Mark, I'm with you for the most part, but that outdoor reset rig on a tank water heater isn't really "helping", necessarily. The proper way to reset with water temps is reset mixing out of the tank.. pulling less out of the tank.
I think in the case of a tank, reset is probably in practice, at best, efficiency neutral. you basically would be "stutter cycling" until the outdoor temperature stops dropping, right?0 -
no open cross connected systems
will be installed by my firm. In my mind they should be a criminal offense - given what's known about bacterial amplification and well-established as factual.0 -
OE & EF
Operating Efficiencies can be dramatically different from Energy Factor ratings. OEs are derived while the unit is in active heating mode to represent the amount of net energy being transferred. EF, on the other hand, incorporates all parasitic energy losses during the 24-hour cycle.
Many standard water heaters, gas for example, will see 82% OE, but a .63 EF. In other words, that unit's overall efficiency is 63%. True operating costs require you utilize the 63%. That's also where the misguided notion that adding a hydronic load inproves a water heater's efficiency comes from!0 -
That's not true Dave. EF is the unit's operational efficiency ON A DOMESTIC LOAD. The parasitic losses are expressed, in that number, as a reduction in the efficiency percentage.
If you are only firing twice a day, and lose that same amount of energy in parasitic losses, you are at a 0.50 EF.
However, if you firing all day long, your parasitic losses are similar, and your ef will then be much higher, because the parasitic loss is much smaller percentage of your overall usage.
Hydronic load doesn't increase operating efficiency, but it WILL increase the overall efficiency of the unit from what it would be if it were used just as a water heater.
right?0 -
I was told
by one water heater mfg that the EF represented an average daily representation for standard usage, which the DOE defines as just under 50-gallons per day per US household.
If intermittent firing causes the .63 EF to drop to .50, them adding a load that will surely result in lots of short-cycling must have an even greater negative affect upon overall EF.
How did you arrive at .50?0 -
Dave's OTM!
"OTM" = on the money!
In the state's/regions I am familiar with codes, using a water heater as a boiler is illegal. Other than a few that condense, and when one considers the size vs. cost of a comparable boiler, the advantages are minimal.
The most obvious "issue" is water content. Most water heaters, start at 40-gallons of storage. Most boilers, at 4-gallons. Having to heat an additional 36-gallons with no direct benefit, unless doing an "open" design - which has LAWSUIT written all over it (pick one: scalding, legionella, controls interfacing, quality, manufacturer's intended purposes, warranty problems, basic product design limitations, etc.) makes no sense.
This is basic stuff. Boilers ae for heating homes and indirects. Water heaters are substitutes for indirects.
Period
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I'm illustrating a point, not quoting an energy factor.
So, your EF is for 50 gallons a day. let's say they assume a 60 degree rise, just to get a number: 60 x 8.3 x 50 = just about 25kBTUs/hr. edit: whups, that's just 25000 BTUs each DAY, not each hour.
they say you have what, 1/2 degree an hour loss? 30 gallons x 8.3 x 0.5 x 24 hours = just about 3000 BTUs/day.
So ON THAT LOAD, the 3000 BTUs/day of standby loss represents 3000/24000 = 12.5% efficiency loss. That is, 12.5% of the total load is lost.
No matter what you do, that 3000 BTUs/day is standard.
However, if you double your usage, it represents a loss of only 6.25% of your usage. If you recalculated the EF, it would be 6.25% higher because of that.
Obviously these are ballpark numbers, but they are to illustrate a point; if you add a heat load of 25kBTUs AN HOUR, you just did a full day's DHW load every hour! the parasitic losses would be very small compared to overall usage... assuming you even have parasitic losses... and so the "real" EF would be much higher than the number you're looking at for DHW production.
So what you would need to know there is the actual combustion efficiency. Which is not rated on water heaters, because they aren't rated as heating appliances. But It's certainly higher than the EF rating. How much Higher? Hard to say. But I bet it's somewhere between 10 and 15% higher.0 -
not to pick nits, but
you'd need one very slow-n-low input at OE to achieve your EF numbers. In reality, the tank will recover in a short (speaking in terms of 24-hour cycles) time frame and then idle. Short-cycling can result in very hot stacking (up to 190F and remain code-compliant) and, as I understand the combustion process, be detrimental to ER ratings. The example you're using will only be accurate for about 10% of the year's heating season. I've witnessed more than a few tankers get tanked into an early grave via sustained flue gas condensation during shoulder seasons.
One mfgr uses density of water at 120F to obtain its weight per gallon for their first-hour ratings, which would represent the weight of lite-water or PR-water in order to boost the recovery rating. Others use 60F for density & weight per gallon to run the calcs. The DOE has detailed charts showing ave water temps throughout the country. They also show where folks set their water heater's unitrol - temp wise & it's plainly evident that 120F doesn't suit the majority of the country for storage temps.
Your numbers need to reflect the overall run time in a 24-hour period to more accurately reflect the EF - if I am seeing this correctly in my minds eye.
Not trying to be obtuse, just trying to understand where or if, I've gone wrong.0 -
Yes, the lower the load the closer to regular energy factor usage you are. And, as you've noted, the energy factor itself makes a lot of assumptions that may or may not hold true.
I'm just saying the energy factor, as rated, assumes that unit is usually not running, and the parasitic losses are thus a relative large portion of the actual usage of the water heater. That throws off the rating of the appliance when used for heating, in favor of the water heater's efficiency.
Whether you short cycle, stack, or what have you depends on the water heater you use, how it's plumbed, how the sensor reads temperature, your load, etc etc etc. i've seen a bunch of water heater systems run fine. I've seen some do what you describe (and reversing flow stopped that issue, but resulted in poor DHW performance during cold weather when the cold return at the top of the tank made DHW to the fixture too cold. Yes, we were using a heat exchanger!).
I'd like to see one with a sensor in the top of the tank, personally. I think that would solve most problems. With a 3-way tempering valve on DHW, and a 10 to 20 degree firing differential. Say, 140 to 120. That would kill short cycling, and utilize the natural buffer capacity of the water heater, and would kill the bad boys you hate so much as well.0 -
a case by case basis, Josh
for small load jobs, lets say under 40K a WH may in fact be a good match.
Personally I think we need to distance ourself from the word "boiler" when taliking about low temperature radiant appliances, let's say under 140F.
Boilers are for making steam, hense the word boiler.
Many fine heating appliances are out their without the label "boiler". The MZ is a fine example of a proven, safe, reliable, efficient heating appliance without ASME badges. The HTP products have been offered without the ASME "boiler" badge.
In all honesty a basic tank WH has a much higher operating and test pressure, 300psi! Has 3 temperature protection devices, Aquastat, ECO, and 210F T&P valve. And is glass lined to last 30 years or more in closed loop applications. Plenty of safety margin for a device that operates at 12psi in a typical hydronic application
Yes you do need to watch for extended condensing mode operation, and also those outdated "boiler" regs
TGhe Bradford White Combi2 is a nice choice for a listed, safe, dual purpose heating appliance.
hot rod
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Rob....
The hotter the stored water, the greater the standby loss, no? Hence, FULL outdoor reset. The heater (theoretically) is capable of operating with inlet temperatures far below 70 degrees F. I say theoretical because when I took the heater out after three years of operation, the insides looked like a 20 year old heater from the flue gas condensation. So much for that stupid theory...Also, theoretically, the lower the tank temperature, the higher the thermal transfer efficiency of the appliance.
Back to reality. In my opinion and experience, if I did a full reset, my stand by losses are significantly negated. Hence, the application of the ODR controller. If it WERE in fact a medium efficiency BOILER, then I would have gone your route, hot deck and mix down to loads.
Remember, this was just one of many experimentations done here at the Eatherton High Altitude Research Center.
ME0 -
And poor ones at that...
(substitutes for side arms).
Did you ever wonder why it is that there are no fire under the tank water heaters over in Europe? It's because they WASTE so much energy.
One of these days, we (Americans) WILL wake up...
ME0 -
Do you really think......
......that using water heaters or open systems will become illegal? Some of the bigger radiant proponents (companies/organizations) advocate/market/use water heaters as their primary heat source.
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They already are....
it is just a matter of enforcement from the AHJ. It states right in the code that the quality of the water shall not be compromised by the heating system. It also states that the appliance MUST have the capacity to supply both of the attached loads at their peak demand condition.
It is no longer approved in Denver, and numerous other municipalities...
If the "industry" thinks they can weather the law suits that they will be facing soon, more power to them. For me and my money, I'd rather spend it some place else.
The lawsuits arer already flying fast and furiously in the UK, and I'm aware of at least three cases locally that are under way.
No one in their right mind will want to be a part of it, regardless of the potential monetary savings up front.
ME0 -
one such co
bragged in public (a meeting) that he knows exactly what areas outlawed the dual use open systems, but that he sells them to HOs to get around the regs. HOs can install, but if a licensed contractor were to do the same, they could be hammered.
In my mind, if anyone knowingly circumvents the laws to gain sales, they're ciminally liable if anything goes wrong. As ME said, it's just a matter of time now. But, we all know how this works in reality. The co selling same goes bankrupt, the principals skate and they open up the next day under a different name.
As for enforcement? That's been a running joke in my area as the current enforcement is just for those pros with a license - everyone else gets a free ride. The PHCC and NFIB have now received reports regarding the state of codes enforcement and the inspection process we are being subjected to in PA. When I get back from vacation, I'll be filing with other agencies to see if we can repair this broken system. We're not allowed to sit in the front of the bus, if you get my drift, and we're the only riders paying the fare.0 -
Yes, you can reduce standby loss, but is that negated by reheating the full tank of water as it cools at night, even if you didn't have a demand that required it? You don't lose all of that excess energy of course, I'm just saying, it's not ideal and I would be more interested in a water heaters used "as intended" that an experimental rig like that, at least as far as making claims about water heaters as a whole. that's all. If you have data from the experiment though I'd love to see it!0 -
Well, if you have 4 gallons in the boiler then you cycle 10 times the rate you have if you have 40 gallons. I'm not so sure that the increased firing cycling rate offsets the residual heat loss. Where is the data?
Scalding and legionella are non issues when you have mixing valves and legionella don't like temps of 120+, so the case against hot water heating using the HW heater is still not too convincing.
There seems to me to be more than enough firepower when you look at a HWH with capacities of 40 gal and a firing rate of 100,000 BTUH (my case). Too much overkill for just hot water and very inviting if you need say an additional 40K of heating .
It could easily be managed without putting a dent in the HW performance.0 -
actually, are you saying that there is never a benefit to buffer capacity?
Cause I'm going to have call shenanigans on that, if so. There are definitely significant numbers of homes out there that benefit from buffer capacity.
Is that enough to recommend a water heater? Not *usually*. But sometimes, yes. In particular, in low load situations. With a heat exchanger, of course.0 -
Scalding, maybe Legionelllan NOT...
If you have potable water laying in a RFH circuit, with no circulation, it is at a nice toast temeprature for the wee bugs. THey're having an ORGY. You and your family come home from a long trip, wife starts washing the mountain of laundry, and washing kids, dad finally get into the shower and turnes up the RF heat before he steps into the shower, and BINGO, direct exposure to massive quantities of legionella pneumophila and a host of other water bourne bacteria. Just because the water heater is set high does not guarantee that you and your loved ones (or customers) will not be exposed.
I've never seen a 100 K 40 gallon tank in these parts. Best we can do is a 75K 75 Gallon unit. Not to say they aren't made, just not readily available in this market.
As for data, why would the water heater manufacturers want to publish data that showed their product to be inferior?
ME0 -
Bock 32E -- 32 gal, 104K BTUH.
Sorry, I thought it was 40 gal, but my case remains.0 -
How would you guys feel about this.
A combined DHW/heating system with a heat exchanger and an HTP Phoenix hot water heater would not appear to be a real bad approach to that type of installation. They have an added solar coil and that might work as the heat exchanger.
It does not have the natural draft vent down the middle of the water tank. It condenses. Has pretty good insulation (1/2 degree per hour I think). Losses from the tank would be the same as a like sized indirect. There could be a conflict when heavy DHW and heating loads are concurrent. A simple answer could be a timer to shut down heating during shower time if it is well defined period. Hmmm. You could also put a sensor on the DHW pipe past a loop blocking convection and disable heating when the pipe gets hot from demand flow.
In some ways it is like a decent condensing boiler with built in indirect and a heating buffer tank. Not as controllable (e.g., outdoor reset), but maybe not so bad. Effeciency is lost to the high water temp, but given the position of the heat exchanger, stratification may help when only heating demand is present. When making DHW the efficiency is probably close to a modcon and indirect. The boiler exchanger sees cooler water than it would if it was having to heat water above the DHW tank temp for heat transfer efficiency.
Just a thought. It is an expensive heater and not a HD special.0 -
Oh, you mean an earl berler..
We don't have much oil around here Zeke. I can count the oil installations around here on one hand (2 fingers actually).
Hospitals that intentionally maintain tanks and distribution systems at or above 180 degrees F commonly find legionella within their systems.
High temeprature is not a final cure.
ME0 -
the ONLY thing I don't like about this method is that you cannot drop the heat source below DHW temperatures, it will always fire to keep the tank at 120 for DHW.
However, that said, it would sure seem to beat a lot of other choices. we have a client using this on a microzoned load and I am personally glad for buffer capacity.0 -
HTP Phoenix
I have designed a couple of systems where the homeowners wanted infloor heat in the basement and floor warming in the bathrooms along with a HUGE DHW demand (12 GPM shower). I decided to use the HTP Phoenix with a couple of Taco X-Pump Blocks to do the trick. The combination works great. High mass, modulation, and condensing in one appliance, what could be better?!0 -
Legionella
ASHRAE says a minimum of 140°F recirculated with a return temperature of at least 124°F, or intermittent flushing with 150°F water.
Apparently a VERY high chlorine concentration (20-50 ppm) is required to kill legionella. The Montana Department of Environmental Quality requires 0.2 to 0.5 ppm free chlorine residual at distant points in a water distribution system. I am not sure what other States require. Obviously that is nowhere near what would affect legionella.
The attached photo shows that heat is the most effective way to kill legionella. Nothing else comes close.
Incidentally, Butte, MT has one unfiltered surface-water drinking water supply. If I had any concerns about drinking the water before I knew that, they are now 20x stronger. It's chlorinated, but not filtered. Nothing like finding a disinfected goose turd in your water glass. With any luck this situation will be remedied soon.0 -
At 140F
the required contact-time is 20-minutes to significantly reduce the free-roaming colonies, but has little to no affect upon legionella that continue to thrive in the outer fringes of biofilms and at the bottom of storage vessels where cooler water settles.
While hot water pasteurization is, by far, the best and most effective means at everyone's immediate disposal, the proper method is rarely utilized. Half-measures continue to be widely assumed to be more than sufficient.
It doesn't help that plumbing codes have turned a blind eye to this issue. CIPH took a good first half-step by mandating elevated storage temps and added a scald-guard mixing vlv at the tank's outlet. Hopefully, they'll lead the way when folks recognize the distribution system and points of use need to be protected to facilitate system-wide protection.0
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