Large Scale domestic hot water

Geoboy_2

This continual issue of capacity shortage is relatively new. When our systems were rehab'd 5 years ago it wasn't an issue. We believe that the system capacity is probably correct for that reason. However, in the past year we are seeing outrageous amounts of water being used in the wee hours of the morning. (I've checked it at 3 AM - averaged about 11 GPM averaged over 10 minute period - laundry rooms not in use! I shut off hot water supply and usage dropped to under 3 GPM. NO ONE COMPLAINED!) Our problem is the nighttime hours are the very time that we expect the booster unit to recover capacity.

Our big problem is the continued failures of the geothermal preheat units. This is our primary motivation for considering the gas conversion.

Based upon the way the building is plumbed, greywater heat recovery isn't an option, at least not economically viable. We really don't want to redesign the plumbing, we simply want to get back to where we used to be, when everything worked better.

Thanks for your response.

geoboy

Large scale domestic hot water

Hi all. I lurk here regularly and have posted several times - find this site very helpful.

We have a large residential building with hot water problems. The building is all electric. Heat and air conditioning are provided by a centralized pump-and-dump geothermal water-water heat pump system, which was upgraded five years ago. Domestic hot water is also electric but is implemented as a two-stage system. Incoming water is preheated by a geothermal subsystem, which can use as a source either 55 degree groundwater directly (winter time) or groundwater which has previously passed through the HVAC geothermal units (allowing recovery of air conditioning waste heat in the summer). The preheat subsystem has 480 gallons of storage. Preheat gets us anywhere between 80 and 105 degrees, depending upon season and load. The preheated water then flows to storage tanks (total 550 gallons), where it is then pumped through a large electric off-peak storage heater to raise temps to about 140 degrees. Output of storage tanks is tempered to 120 F. There is also a building recirc loop.

We have been having problems with both the preheat and booster subsystems. The preheat units have failed numerous time due to water quality issues, while the booster heater is a moldy oldie - the original manufacturer is long gone and parts need to be custom fabricated.

Currently we are plagued with periodic shortages of hot water. Part of this is due to equipment issues, and part (probably the bigger part) is due to waste of "free" hot water by building residents.

We are considering replacing both subsystems with a single gas fired system. The idea is to eliminate the preheat subsystem and replace the booster unit with several gas-fired units in parallel, leaving the 550 gallon storage tanks, recirc loop and other piping intact. We are considering such units as the Munchkin VWH or equivalent.

It has occurred to me that tank-type high efficiency condensing water heaters (such as A O Smith Cyclone, HTP Phoenix, etc.) could also be used as the heat source. Although I realize that potable water boilers are normally used in such large-scale applications, using tank-type heaters does have the advantages of giving us extra storage on tap to help combat spot shortages during peak usage. I am also curious as to the relative advantages of boilers vs water heaters regarding product longevity, resistance to debris in water, etc.

Do any of you hot water experts have any information? Your assistance is greatly appreciated.

bigugh_4

Look at Lockinvar Heaters.

I once replaced an electric system with one of their instant type heaters. It worked very well. No storage tank needed as the water was circulated around the hotel and back to the heater. I installed it according to their (lockinvar's) instructions. the water was tempered as it left the boiler room.

tim smith

Another option, ASME plate and frame heat exchanger with

condensing boiler(s) and storage tank(s). You could also parallel or series a second plate and frame for waste heat of a/c or even for solar in future. Would be pretty cool I think. I have done the Triangle tube boilers & plate and frames w/ tanks for 160 unit apt bldg in past year or so and works well. Good luck, Tim

Mark Eatherton

Lochinvar Armour...

Gioninni in an non ferous jacket.

In a one for one replacement over a tank fired system, they can reduce the energy consumption by a minimum of 30% just due to the change in combustion technology. And they modulate!

ME

geoboy

RE: Plate and Frame...

Our preheat subsystem consists of two 2-stage water-water heat pumps which impart heat via a plate & frame exchanger to our 480 gallon storage tank array. There is a noticeable loss through the exchanger (the surrounding room air is fairly warm). Also, both sides of the exchanger need to be pumped 24/7. Seems to me that running the potable water through either a boiler or tank-type heater designed for the purpose would be more efficient - reduced pumping cost and no exchanger loss. What am I missing?

geoboy

Mark

I've seen your posts out here for a long time and have come to respect your input. Lochinvar vs Munchkin - is that just brand preference? Don't know the relative costs, and we don't need Lochinvar's fancier control system. (We have a Honeywell Excel 5000 DDC controlling the entire operation). Any reason to consider either the Munchkin? Waht about tank-type heaters like the A O Smith Cyclones or Munchkin Phoenix? (We are in Massachusetts - hence the interest in a locally supported brand.) Should we even be considering the tank-type approach?

BTW, we have over 300 units here, primarily one bedroom.

Jack

Step one

IN my opinion is to deal with the water quality issue. You state that you think the current equipment problems are in large part water quality related. Regardless of the type of material used in the newer system, poor water will rapidly deteriorate performance of high quality materials through scaling, etc and while you will be happy for a while, it won't last and it will end up costing more, sooner than you thought.

Listing the equipment types in no way provides the information needed to size your system properly. How many apts in the building? What type fixtures and flow rates from those fixtures? In any hot water design you want to look at water conservation steps as a part of the design. Can you do that? It can have profound affect on the system design.

Can you provide that information?

Mark Eatherton

The difference...

is primarily in the control logic, and the quality of construction. At the bare roots core, they are both Gioninni heat exchangers.

The thing that bothers me about the Cyclone is that it is a glass lined steel tank, which means that the flue gas passage ways that the condensate will be trickling through are mild steel, and it has been my experience that mild steel and acidic condensate don't like each other. I would love to be proven wrong, but the tank type of heaters of Smiths that I have substantial history with (mild steel with magnesium or aluminum anode rod) have a specific finite life expectancy, and when the tank is exposed to the process of combustion, the life expectancy of the tank is significantly reduced.

HTP's Phoenix is a stainless steel tank (not sure which one, and one would want to check for chlorides in the water before spec'ing) which SHOULD have a significantly longer life expectancy.

A word of caution on applying the Gioninni heat exchangers in potable water applications. If you have hard water (lime scale accumulations) I would STRONGLY recommend the use of a magnetic water conditioner to avoid the eventual plugging of the heat exchanger due to lime scale accumulation. I have successfully applied Superior Magnetic water conditioners, and they use to do a free water analysis to determine if they can be effective.

I know a lot of people here think they are BS, but you can't employ hundreds of people since 1964 selling garbage... It works in MOST cases. (will NOT address "glass water" or silica scale accumulations found in parts of Texas and other southern states).

Seeing as how you already have a fancy control logic with lots of I&O, you should consider doing a DHW programmable set back. ASHRAE has some clear cut ideas of the hourly demands for this type of system. During peak loading, raise the storage tanks to 140 degrees F (assuming anti-scald mixing valves on the outlet), and during no peak conditions, turn the system down to 130 degrees F. Doing so will reduce the in building standby losses anywhere from 15 to 30 % of base consumption. Between the application of this technology and the highly efficient sealed combustion technology, you could reduce their energy consumption by 30 to 60%.

Don't forget to control the DHW Circ Return as well. That is responsible for the majority of distribution losses.

Thanks for the kudos, and thanks for being a part of the community.

ME

geoboy

Mark and John...

John:

Regarding water quality issues, we have two types. The failures of the geothermal preheat units are due to high iron content in the ground water, and the bacteria that are indigenous to that water. We have filters which have been known to clog rapidly, starving the heat pumps. Although they will shut down on safety (freeze protect and/or low pressure), sometimes by the time the shutdown occurs we've already experienced freezing in the evaporators. We've lost about a half-dozen evaporators and compressors as a result over a five-year period. We even added diferential pressure switches to the preheat units to try and detect clogging filters, but they are only partially effective. Our HVAC heat pumps are also exposed to the same garbage in the ground water, but due to lower operating temps and duty cycles they are relatively unaffected - no failures thus far!

The second type of water quality problem to which I refer is in the potable water itself (which does not pass through the geothermal heat pumps). These problems have been less serious, but do comprise a nuisance. We do have some scaling, which has led to replacement of tempering valves on the storage tanks. We also periodically take on significant amounts of debris in the incoming water, courtesy of the municpal water department. This normally occurs after water main construction (of which there's been a lot) or flushing of the fire hydrants (a semi-annual event).

Regarding system load, we have over 300 units in the building, Each has one kitchen and one bathroom. About 35 - 40% of the units have dishwashers. No laundry equipment is permitted in the units (although we've found some anyway). Our two laundry rooms contain 10 washers each. Most of them are EnergyStar compliant front loaders.

We are about to embark on a comprehensive program of unit inspections, looking for unrepaired leaks (over the years we've found some whoppers), multiple head showers, hot tubs (yes, we've had them too!), etc. We are also checking for cross-feeds through malfunctioning mixing valves on plumbing fixtures or equipment connected to mixing faucets left on all day.


Mark:

I've been looking at the Lochinvar website. Am I correct in assuming that their Armor is the DHW equivalent of the Knight, just as the HTP VWH is the DHW equivalent of the Mucnhkin?

We haven't considered nighttime setback of the DHW temps because we don't have a clearly defined off-peak period. We have a lot of younger people here as well as night shift workers, and people come and go at all hours. We do detect excessive usage at night, and have for the past 4-6 months. We believe that some of this is illicit. We just busted someone for having a forbidden washing machine in her unit - turns out she was doing laundry for hire!

We have a pretty good handle on the DHW recirc loop. It's controlled by an end-of-line sensor, and attempts to maintain a value of 103 degrees at that sensor, whose location is fairly distant from the nearest apartment. A temp of 103 at the sensor equates usually to 110 or above at the worst-case usage point. We also suspend recirc when the tank temps get too low.

I am intersted in finding out more about magnetic water conditioning. Do you believe it has the potential to address both water quality issues as described above?

Thanks for your responses.

Mark Eatherton

Yup and nope...

Yes, the Armor is a Knight in all non ferrous clothing.

And no, I would not recommend you use the MWC's to address the bacterial iron problem on the GSWHP side. They would only compound the current situation you have.

Instead of pump and dump, maybe you should consider the possibility of a closed loop system or one of the new closed loop large surface highly conductive heat exchanger that they can set down the hole...

Seems like it would be cheaper than replacing evaporators and compressors in the long run.

As for sizing DHW heating systems, I have always depended upon the RayPak DHW sizing guidelines. They give you the basics, based on an 80% draw down factor along with recovery factors, and if you want to shift those numbers around, you can, so long as you maintain the bottom line number of BTU's that they call out. Has never let me down.

ME

tim smith

True on the extra pump needed. Although you do reclaim the heat

from the condensor which is free offsetting the cost of gas you will use to heat the tanks. I would be more inclined to lean towards the heat exchanger idea along w/ maybe a tower for cooling when dhw demand does not take up the heat. Just a thought, also you would do away with the the scaling problem on a closed loop. Just conjecture at this time but could be viable??? Ideally you would run a closed loop to ground loops for heat pumps and steer off water to heat exchanger for dhw when needed. That I think would be the best of all worlds. Tim

geoboy

Heat Exchanger down the hole??

OK, thats a fascinating concept! We have two 78 ft deep wells, which we use alternately, although we can run them together if need be. Under peak conditions we need as many as 500 GPM to satisfy the mid-winter load for heat and DHW. (we cool that water approximately 8 degrees.) What sort of heat exchanger could fit in the wells capable of passing the equivalent number of btus?

The previous version of our system used a heat exchanger between the well water and the heat pump loop, which consisted of two 200 ton Chrysler Airtemp chillers. Maintenance was a nightmare due to fouling of the exchangers. Once fouled, we were unable to satisfy the winter BTU requirements of the heat pump system. We replaced the exchanger several times first going from shell-and-tube to plate-and-frame, and then re-plating the plate-and-frame units twice. Of course we were also running 15 HP worth of pump 24/7 to drive the intermediate loop. The existing system eliminates pumping an intermediate loop and allows us to run the well pumps on VFDs, which provides substantial energy savings.

The seven HVAC heat pump units show minimal problems from the well water environment. The two DHW preheat units are the problems, despite the fact that they are almost the same model and are connected to the same well water. The difference is the duty cycle - the DHW units run a much higher percentage of the time. There is also a difference in the length of the piping - the DHW machines are closer to the well water source than are the HVAC units.

If there is any way an appropriate heat exchanger can fit down the hole and satisfy our BTU load, I'm all ears, particularly if it can be done more cheaply than replacing the DHW system. Any data on such a device?

Larry Weingarten

I'd really like...

... to see details on DHW load. Could be something as weird as sub-metering would substantially reduce the usage by discouraging waste; for example. Drain heat recovery, demand pumping, main and twig plumbing and fixtures each may have a place in cutting the load. Once the load is reduced appropriately, the heating equipment will certainly be simpler and less expensive, now and on into the future.

Yours, Larry

Mark Eatherton

Sorry...

I was between homes. I tried googling the heat exchanger and came up empty. I do remember getting information on one in the email at work though...

Claimed to be able to do the work of three wells with one as I remember. Not sure if it would work or fit in your situation. Will try and see if I can find it tomorrow.

ME

Mark Eatherton

Sounds like a leak to me...

Under floor/ground distribution?

ME

geoboy

Nope, no leaks we can find.

All of the piping is aboveground, either in the units or in pipe chases. When anything leaks something or someone gets wet, or else we see unexplained puddles in the basement. We can then track down the leaks.

As explained above, we believe there is some illicit or at the very least, irresponsible usage in the building, which we are slowly attempting to track down. Renters never admit to anything!

[Deleted User]

Threaten them...

with the potential individual DHW usage/billing system if consumption does not drop, and see what happens.

"Not in MY wallet you don't!!!"

Works everytime. So long as residents perceive that ANYTHING (heat, water, hot water) is "FREE" they WILL waste it.

No luck trying to find the email either. Still looking in the archives.

ME

geoboy

Actually, we've thought of that.

So much so that we let it slip through the building's rumor mill that individual meters may be considered!

Meanwhile I've been checking daily water usage in the building over the past week. Since word got out about the impending inspections and possibility of individual metering, daily GPD has dropped a little. Don't kow if it's a pattern or simply a fluke!

Thanks for your effort. After reviewing everyone's posts, I'm still unclear as to whether we should consider using stainless water heaters such as the Phoenix (apparently the Cyclone is out) or non-ferrous boilers such as the HTP VHW or Lochinvar Armor. In your opinion, which of the two approaches would be more economical over the long haul?

Randy_30

FYI the Phoenix tank is 316L and the exchanger is cupernickel.

hot_rod

Solar component an option?

It could provide a portion of the DHW and maybe help with the geo side.
30% tax credit on commercial, possible state and utility incentives.
hr

tim smith

Maybe someone is doing some Hydroponics farming, has

your electric bill went up also??? Hmmmmmmmm.

Tim Weaver

Leaking faucets

As a building ages faucet seats start leaking and even though viewed one at a time it doesn't seem like much, the combined volume can get pretty serious.

Tim Weaver

Check the Sewer

If you have a singular Building drain; look in the cleanout and look at the meter during the off-peak hours. Also dress up like an investigator and prowl around at nite with a listening device.
Sometimes mixing valves (shower, etc) can allow hot to migrate into the cold lines where it might get used as toilet tank fill or lost out the discharge of reverse osmosis point-of-use filters (these waste a lot of water).
Also look outside the building for leaks running down the outer foundation.

Unknown

Mark thats not fair

its not just the people here that think they are BS.
http://resources.cas.psu.edu/WaterResources/pdfs/magnetic.pdf

seabee570

problem

does your honeywell ddc system have trending?If not it could probably be installed,you could then trend and print out your usage patterns.Another additional controller made specifically for your domestic hot water control might also help.I have found a control made by fluidmaster is very good. I cannot think of the name of it.essentially it trend usage and has a setback and recovery feature.I have used them at 3 different types of facilities and they work well,and save some money