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Hot water heater argument

Hot water heater argument

Hot water heater argument

(OP)
  Hello all. I am hoping someone here can answer a question that would seem a no-brainer to me but, not being an electrical expert, I thought I'd pose it here. What it is, the facility where I work is on a electricity usage reduction program and are looking for anyway to cut back. One thing that was brought up was the use of hot water heaters. As it turns out we have quite a few in and around the plant.
  The question is, would it be advantageous to replace the 4500 watt elements in most of our heaters with 1500 watt elements? My boss claims that this would save a lot of power. I really don't see it. It would seem to me that it takes a certain amount of power to get a certain amount of water up to a certain temperature. The only thing a lower wattage element would do, in my opinion, is to lengthen the time it takes. Is he correct or am I?       Thanks, Ballpeen.

RE: Hot water heater argument

Yep, lower wattage element means more time.  It takes a certain amount of energy to raise the temperature of a specified amount of water a specified temperature.  Energy is power times time, so 1/3 the power means 3 times the time.  The big risk of changing the elements is that you might not be able to keep up with the water usage.

RE: Hot water heater argument

Depends on the useage, but you are closer to being correct. If the hot water is used a little bit but all day long where the elements are on all day to replace hot water used, then he may have a point worth considering. Part of the reason is that a lot of hot water is wasted replacing cold water in the pipe, that's why you have to wait for the hot water to "get there" if the heater is far away. If the hot water is being trickled through semi-regularly, the losses would be slightly less (assuming the pipes are insulated). If the hot water is used in big slugs and replaced only a few times per day, you would be right because the amount of waste would be minimal compared to total useage, and the energy to heat it is essentially the same.

A better idea is to do what people elsewhere in the world  have been doing for years, replace the big heaters with small instant heaters at the point of use. They don't store the hot water, they heat it only when you use it. Cuts down the losses to absolute minimum, and hot water is right there when you want it.

Eng-Tips: Help for your job, not for your homework  Read FAQ731-376

RE: Hot water heater argument

Most facilities would be more interested in reducing their PEAK load (called: load shedding).

Therefore, what you would want to do is put in a control system so that all non-critical loads (and hot water heaters are typically ideal candidates) can be temporarily turned off when the essential loads start to climb. Since the tanks are full of hot water, if the power turn-off is not excessively long, then nobody will even notice. In the worst case, you might need to replace 40 gallon tanks with larger 60 or 80 gallon tanks to ride over the load shedding gap.

Instant 'On Demand' water heaters have some advantages, but they would be the exact opposite of what most facilities would be looking for if they're trying to reduce the peak load. Most tankless 'On Demand' water heaters need 7 or 8 kilowatts. That's a higher peak load than a normal tank.

Or switch to natural gas or oil fired water heaters (yuck).

Saving power overall (not concerned about when) means putting in water heaters with better insulation, closer to the tap (less running the tap waiting for hot water), insulate the pipes, slab of insulation under the tank, ask people to use less, etc. This is where 'on demand' heaters can help.


RE: Hot water heater argument

You should always look for ways to reclaim process heat into heating or preheating the water heater water.  If you are running any kind of cooling systems,(cooling towers, radiators, fans), check out reclamation.

Keith Cress
Flamin Systems, Inc.- <http://www.flaminsystems.com>

RE: Hot water heater argument

Right on itsmoked.
The reclaimed heat doesn't have to do the whole job. Any preheating of the water before it goes into the existing hot water tanks is benificial.
A heat exchanger on an air conditioning system through which the refrigerant flows on its way to the condensor and through which the water flows on its way to the existing hot water tanks would be a win win situation. Lower head pressure and so more efficiency for the air conditioner, and preheated water for the hot water tank.
In times of light demand, the cost of energy for the smaller elements will be about the same as the larger heaters. Half as much heat for twice as long. The real saving is when the demand is high and people must use luke warm water because the 1500 watt heaters can't keep up to the demand.
Another energy saving technique that doesn't work very well is to just set the thermostats lower. The heat loss through the insulation of the tank will be slightly less but not enough to worry about. The users will just open the hot water tap wider as they mix the hot and cold water to achieve the desired temperature. The hot water will be at a lower temperature so the users will use more of it to compensate. Same energy bill in the end.
yours

RE: Hot water heater argument

waross, your points are much more valid if in fact the hot water is being used by people, particularly people who won't whine about a lack of hot water (or people who's whining will be ignored by those who make the decisions), but your points don't work well if the hot water is used by a process that has specific temperature needs.  The OP doesn't state the use of the hot water, so I don't know.  Hot water for hand washing, and the plant has a demand charge there might be some cost savings, but the pay back will be loooooong; hot water for most any other use, or no demand charges, the change may cause more problems than it solves, and the payback might even be negative.

RE: Hot water heater argument

Hi davidbeach
I'm sorry if I didn't express myself well. I agreed with your original post and I thought that my post was complimentary to yours. I think I agreed with your latest post.

"The hot water will be at a lower temperature so the users {Proces or hand washing} will use more of it to compensate. Same energy bill in the end."
respectfully



RE: Hot water heater argument

waross, sorry, my attempted point in my 23:36 post was that process uses may draw the hot water faster than the lower wattage element can keep up with and the only way to maintain the necessary temperature is with the higher wattage element.  Using more won't help if the temperature isn't high enough.

If the lower wattage element can keep up, than hand washing or process won't matter, and it is just a matter of the lower wattage element being on longer.  But if the lower wattage element, even on continuously, can not heat a sufficient volume of water to a sufficient temperature, then the attempted replacement will fail.  That's all, otherwise I think we agree.

RE: Hot water heater argument

As mentioned, On-demand heaters are typically 7 or 8 kW. That sort of indicates that is the sort of power required to keep up with most normal demands.

In other words, it's obvious that 1.5kw wouldn't.

RE: Hot water heater argument

If the hot water draw from a particular hot water heater is intermittent, then the on-demand (or flash water heater) is the way to go. They are used extensively in Europe to save energy. In many situations it makes no sense to keep large tank of water hot all the time.

However if the water is in continuous use, then going to a on-demand or even changing elements won't save energy.

RE: Hot water heater argument

Is this a 24/7 plant? If not, timers may help. Heating elements cycling on and off during periods of non-use waste the energy that is lost through the tank insulation. Warm water losses less energy than hot water does through a given insulation level. Set the timers so the water is hot prior to use. Demand charges and time of use may complicate matters though. If all the water heaters now switch on simultaneously during high load hours, the savings might be negative.

RE: Hot water heater argument

"...makes no sense to keep large tank of water hot all the time..."

The standby losses can be reduced. In my own house the hot water tank has some sort of high-tech foam insulation (maybe R14). It's wrapped with an after-market insulated tank blanket. The tanks sits on a 2-inch slab of foam (R10). The cold line has an anti-siphon trap to block any convection circulation into the cold supply. All the pipes are insulated. I'm fairly confident that my hot water heating bill is primarily consumption driven.

OP really needs to double check about overall consumption versus peak load. The approaches can be opposite depending on the goal.

RE: Hot water heater argument

Energy savings is more than just the standby losses. The on-demand water heaters can be located very close to the point of use. Not only do you save running water until it's hot, but you save that hot water left in the pipe afterwards that just cools down. And, if you are in a warm climate, you save the AC cooling resulting from standby losses and the wasted hot water heat.

RE: Hot water heater argument

(OP)
  Wow, I didn't expect so much input. I guess our facility's water heaters would be considered to be occasional usage only. Practically all the heaters are for hand washing only. So lower wattage elements may make sense and as it turns out they're not all that expensive. I agree that we should replace our heaters with point of use type, but that will only be done as the older ones start leaking. We are currently monitoring our water heaters one by one with a wattage meter to see just what is actually being used on a day to day basis. Many of these are Mon.- Fri. and could be off over the weekends.
  Right now I'm being told that "everything" is on the table as to electrical cutbacks. Even possibly moving our primary shifts to after peak hours instead of the traditional 9 to 5 environment. The reason being is that out electrical expenses have jumped to $1,000,000 over last years cost, or so we are told by our upper management. I guess some negotiating has been going on and we were able to shave off a considerable amount but, we still need to save more.... It never ends.
  As far as heat reclamation, there is quite a bit of that going on already as our company is attempting to become as "green" as it can be. We try to save all the btu's we can.
  Maybe the best thing to do is wrap the heaters with insulation (fairly cheap), install lower wattage elements ( also fairly cheap) and call it a day, where the type of timers we would need cost around $90 ( from Grainger's),  it would take a while to recoup the $$$$$.
  Does anyone have any magic "bullets" that would save a manufacturing company with mainly motor loads some $$$'s on electricity? And yes, we are cutting our lighting as well. My boss says that what we are doing will only make about a 1% difference in our overall bill. But you can't get the people in the Ivory Tower to understand it.   Ballpeen.

RE: Hot water heater argument

You could do what one of my general managers did: put timers on the copiers (what a dork).  

While it saved money on the utilities, it cost 10 times more in labor than the savings in utility bills.

TTFN



RE: Hot water heater argument

ballpeen;  When your kind of question comes up the FIRST thing that must be looked at is your "rate structure".  Because the biggest punishments dished out by suppliers can be due to power factor(yours being possibly)bad,  and peak load penalties, a penalty charged because the power company has to have available enough capacity for your highest load time.  Until these two questions can be answered, a whole lot of our suggestions would be flat wrong or ineffective.

That said a company with many millions in electrical charges should really have someone brought in to actually assess the zillion possibilities that are probably available in a place that large.

What kind of business are you? Textile? Food?

Keith Cress
Flamin Systems, Inc.- <http://www.flaminsystems.com>

RE: Hot water heater argument

Please reread your initial doubts and Davidbeaches response. The lower wattage element will use the same energy and cost you in material and labor. Big deal if it's cheap, there is no payback, ever.
Now that I know the use, I have another suggestion. Hand washing requires warm, not hot water. You may be able to lower the thermostats. The possible downside might be insufficient warm water since more will be drawn from the tank and less from the cold water supply. As I stated before, more energy moves across the insulation from the hotter water. Somehow I suspect heating water for washing hands is an insignificant part a 1M increase.

RE: Hot water heater argument

There are always exceptions, but many people who have used On-Demand water heaters are not that fond of them. I have several types in a lot of different places. I have used both gas fired and electrical. Your primary control of the temperature is the flow rate. It's really exciting in a cold climate to try for a hot shower. When the incoming water is very cold, the shower is just warm. You keep trying to cut back on the flow to get the water warmer. Then the flow switch cuts-out on low flow. Instant ice water. Now you have to turn the flow wide open to get it to start again, while trying to get out of the spray. One repair bill can wipe out a couple of years savings. I have seen and worked with the 7 to 8 Kw On Demand units. They were commercial units used to pre heat water feeding an institutional dishwasher. The dishwasher heats its own water, but that takes time. The wash timing cycle doesn't start until the water has reached a certain temperature (Set by the local health board).
When the demand for clean dishes exceeds the machines capacity, some suppliers increase the hourly through put by putting an on demand preheater ahead of the dishwasher to speed up the heating part of the cycle. The last one that I saw had a dedicated service and revenue meter.
yours

RE: Hot water heater argument

Back to your primary problem.
I would suggest that you counter the smaller element suggestion with a better insulation suggestion. Better insulation for both the tanks and the hot water lines.

Aside from the water tanks, the first thing to check is your power factor, but I would guess that with a power bill like yours, any power factor penalty would have been noticed long ago and corrective action taken.
From the size of your bill you should be considering your own generators for peak shaving and/or co-generation. The economics depend on the relative demand charges, the cost of fuel, and the utility's willingness to buy peak power and pay a good price for it.
Do you have natural gas on site?
With a generator you will probably be able to heat all the water that you will ever need.
Do you use a lot of air conditioning or refrigeration? Using hot gas to preheat your water ahead of the hot water tanks has the potential for double digit percentage savings in water heating costs. Even solar water heaters will save a lot of water heating costs. Again use them as preheaters and let the electric heaters supply the final heating and control the temperature. That keeps the new system transparent to the users and no-one will be inconvenienced.
A good question to keep things sane is "How much a year does one of these units (Hot water tank, copier, whatever) cost to run, how much can we save and what will it cost to change it?"
Or if you prefer, "What's the cost benefit analysis?"
yours

RE: Hot water heater argument

(OP)
Thats some good advise given there, particularly waross. As stated my super has said right along that with all of these electrical reductions your only looking at "pennies" and I think after what I've seen for numbers he's probably right.
  Yes, there is talk of doing a cogenereration in conjunction with our steam boilers but, again  my boss says you need a cooling tower to keep a constant vacuum on the discharge side and engineering doesn't think its needed. We'll see how it all works out in the end.
  Itsmoked, I work in the maintenance dept. of a textile plant. As an assistant to the dept. manager. I'm the guy that usually ends up on all of the projects that my boss doesn't want to do, and this electrical reduction is one of them.
  As far as the rate structure, that is constantly being worked on from what I understand.
  No, we don't have natural gas there. We primarily burn wood and use #2 fuel oil as a backup. And no, we really don't have a lot of A/C or refrigeration either. One thing that we do is take our hot waste water and use it to preheat our process water and we also have a couple of water cooled air compressors that also preheat water and those work quite well. Although the heat exchangers keep having the tubes go bad, but thats another story altogether.

RE: Hot water heater argument

I hear you waross.. I drove over to the next town (30min) and bought an demand gas water heater when our old 50gal started leaking.  Got back and started reading the manual..

1) Water lines came out the bottom... Not an insignificant change to existing plumbing.
2) Required a 6inch flue.  Up from exiting 3 inch?
3) Required a 1 inch gas line from metering point!!
4) Wouldn't come on at less than 3/4 gal/minute.

I took it back.

It costs about 37.5millicents to raise a gallon of water a degree F.  So carving a bunch of degrees out of water heating by preheating is a great spot to start.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Hot water heater argument

ballpeen,
First off, I'll reiterate the comments about hiring an expert on this. $1 million is a lot of money as an increase, even a 10% recoup in the first year would more than pay for the consultant.

For example, like others I would also suspect power factor penalties.  The peanlties often work out as multipliers on your basic rate, so even if appears that they have negotiated a good rate for you, they jack the net dollars up by sticking you with a big penalty for poor pawer factor. I'm not bashing the utilities here, power factor costs are very real to them, but often they are in the business of selling you on THEIR solution, which is for you to pay for thoses costs, rather than mitigate the cause. You mentioned using cooling water from large compressors to preheat process water. Large facility compressors are often a good candidate for running synchronous motors as synchronous condensers to improve the power factor of the entire plant. Not cheap, but possibly a quick payback if you are getting hit with big penalties.

There are also very (relatively) low cost Demand Reduction Systems that act as energy watchdogs, monitoring and mitigating your peak demands, another utility rate multiplier, by shedding loads on a prioritized basis.

Getting an expert on board to investigate your needs and suggest the myriad possibilities would be well worth it. Fluorescent light bulbs and water heaters are not ging to make much of a difference in a $1 million anual increase I'm affraid. Not unless you have about 4 million incandescent bulbs!

Good luck with that.

Eng-Tips: Help for your job, not for your homework  Read FAQ731-376

RE: Hot water heater argument

We've been looking hard at energy savings too. A 60% increase in electricity prices kind of impacts the bottom line.
We're a teeny tiny factory in comparison to most people here I would guess, and the cost of changing things just wipes out any payback. We tried looking at cogen but our processes just aren't suitable as our ovens high grade heat, not low. Solar and wind are so expensive and difficult to integrate that we'd never ever recoup the cost.
All the seminars we can go to ever tell us to "turn off the lights in empty rooms, and shop around for your supplier. No sh*t Sherlock!
All we can do practically is to add insulation to everything to reduce heat losses in the process.
No environmental grants available for us to help us do it either. (The Government must have spent all the money on their £500,000 shiny new walkway.)

So I'd agree: lag everything you can, and see if you can reduce the temperature of the water for hand washing (and the processes too: even 1 degree C reduction will help)

Rob

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

RE: Hot water heater argument

"...on-demand water heaters can be located very close to the point of use..."

This implies that one might have several on-demand heaters distributed around the facility (or, for home use, around the house). Sounds like a good idea. But...

Each 7kW unit probably draws about 30A from a 240v feed.

For home use, if you have one appliance (a dishwasher for example) filling with hot water, one person taking their morning shower and a couple of people decide to wash their hands in different washrooms, then you're looking at an instantaneous current draw of perhaps 120A (240vac). Add in some other loads (like space heating and a water pumps) and your 200A service suddenly starts to look inadequate.

In other words, for home use, the advantage quoted at the top may not be as practical as it might appear.

And for facilities, such uncontrolled peaky loads might be the exact opposite of what is required to reduce the electricl bill.

There are small (eg: 5 or 10 US gallon) 'normal' water heaters that can provide another solution with fewer drawbacks. And they're much cheaper to boot. Might be ideal for isolated bathroom sinks.

RE: Hot water heater argument

Hey RobWard do your ovens have stacks with heat exiting?

Just curious.

Keith Cress
Flamin Systems, Inc.- <http://www.flaminsystems.com>

RE: Hot water heater argument

A further possible problem when changing elements is finding the flange underneath is composed of rust. Old element kept the rust in place and prevented leaks, but the new one will never seal. The cheap job has suddenly become expensive. Here's a link to a very efficient water heater that solves the rust problem too. http://www.marathonheaters.com/

RE: Hot water heater argument

A quick fix for under utilized tanks is to remove one of the jumpers to the bottom element.  It has the effect of reducing the effective volume of the tank. It is quick, there is no problem with rust, there is nothing to buy, and if the jumpers are saved it is quickly reversible.
I don't offer this as a solution, but rather offer it on the theory that if management is going to do something with a small probability of success, let's steer them to something cheap and reversible (If you can't make your boss look good, try to keep him from making himself look bad). It will almost certainly reduce consumption and there are almost certainly going to be enough complaints that it will be reversed. Myself, I would probably suggest it to management on that basis. However I have virtually no corporate survival skills whatsoever.
And what the hey. In a big plant there are probably several tanks that are under utilized and would profit from this kludge.
yours

RE: Hot water heater argument

Itsmoked,

no they don't. (Well, not intentionally anyway)

Back to water heaters though; you mentioned these in another thread I started asking about generators:

http://www.whispertech.co.nz/main/acwhispergen/

2 birds, 1 stone...

I wonder if they'd be of any interest to th O.P.?

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

RE: Hot water heater argument

Hello RobWard
Here's a web site that may be valuable when evaluating sterling cycle devices (As in the link above.)
The web site information appears to be about 4 years old and may be out of date. It will give you the questions you will want answered when evaluating a sterling engine, and hope that new developments have changed some of the answers.
Yours

RE: Hot water heater argument

Still, how many water heates are we talking here?

Let's review Econ 101; "run the numbers before taking action". If all your heaters were reduced from 4000 to 1500W, each ran only 2 hours per day cumulatively, 365 days per year and you pay 10 cents/kWH, you would save $219/yr per water heater. You need to have 4566 water heaters to end up saving $1,000,000/yr, and of course the first year you would have to suck up the $100 guesstimate for parts and labor per heater, which comes to a whopping $456,000 initial outlay. I still say you have bigger fish to fry first. Play with the little stuff after you make a big dent in that increase.

Eng-Tips: Help for your job, not for your homework  Read FAQ731-376

RE: Hot water heater argument

I don't know how I missed the reference to steam and co-gen.
Re the cooling towers. The answer is yes, no, and maybe.
It depends on the whole layout.
I'll try to give you an over view so you can talk intelligently.
There are two types of steam turbine, (I have allready commited a faux pas because there is also a third type that combines the first two but later for that).
A condensing turbine typically takes steam at boiler pressure and discharges into a vacuum. This needs a lot of cooling and a water tower is a good way to provide the cooling but not the only way.
A non condensing turbine typically takes steam at boiler pressure and discharges steam at a lower pressure. No cooling needed. A 150 psig boiler may feed a noncondensing turbine that discharges steam at 15 psig for use in a drying cycle. This type of turbine may often be bypassed with a desuperheater which is cheap and simple and will convert high pressure high temperature steam into low pressure low temperature steam. If your turbine goes down, your other process continues without interuption. Also, if your process demands more steam than the turbine can deliver the desuperheater can be configured to automatically kick in and supply the excess steam again without interuption to your process.
The choice depends to a great extent on what you have in place, the availability and cost of fuel, the availability of capital, and your intended mode of operation. If your boilers have more capacity than you are using you may opt to just use the excess capacity to generate part of your electrical needs. With an assured supply of cheap fuel, you may opt to go new higher pressure boilers and supply all your electrical needs, or generate and sell an excess.
The third type of turbine is a multi stage turbine that supplies steam at one or more intermediate pressures and condenses the balance.
In addition to a cooling tower, a river or a lake may be used for cooling water. Watch out for environmental issues because of the increased water temperature of the river or lake. I read a paper on a co-gen plant whose output was limited by the allowable temperature rise of the stream they used for cooling. When the water flow was down they had to curtail generation to avoid heating the river over the limit set by the local environmental board. I read about a nuclear plant whose discharge of warm water into a lake gave rise to an explosion in the mussel population in the vicinity of the discharge.
In a sawmill environment, lumber can be pre-dried by placing it in front of the air discharge from radiator type coolers, but that's a poor mans solution. Either poor in capital or in water for a water tower.
I hope this is enough information for you to interface between your boss and the engineering staff or at least ask intelligent questions.
yours

RE: Hot water heater argument

(OP)
   I didn't realize that you had a non-condensing type of steam turbine available. That looks like a viable option. Maybe thats what our engineering dept. is looking at right now? Based on what my boss is saying, he evidently isn't aware of them either.... There is a river nearby but, this company is dead set against any discharges into it. Even if they are benign. What they want is a "closed loop" way of thinking, where we actually throw nothing away, if you get my drift. Heck, if we do have a spill, its a major event.
  One thing that is going on at this plant is that the facilities engineer and my boss, (a master electrician and maintenance dept. head), have what seems to be an ongoing feud. Its a long story but, each of these guys are constantly trying to prove each other wrong. Usually the engineering guy comes out on top as he has the upper management on his side, even if the outcome doen't make a lot of sense. I have to be careful what I say because I can get my boss in trouble very easily.  
  Of course, we are using a wattage meter to check our H.W. heaters to see just what they are consuming. That way we can make a sensible decision as to what our best options are. Whether to put timers on or just wrap them with insulation. Removing the jumpers are something that I haven't heard yet. Do all these heaters have them? I'll run it by the boss first and get his input on it. I know what you mean stevenal about the element removal, sometimes its a nightmare.
  I am not sure if they have checked into hiring an energy consultant or not. It probably would be worth while, but all I can do suggest it. Actually hiring this person would ultimatly be up to someone higher up the food chain.
  One thing I'm sure of is the monitoring of the power factor. And it runs close to .80 to .90 as a rule. Where the cloth is woven, the room where the disconnects are, there is a digital readout that tells the P.F. constantly. And I've been told there is a large bank of capacitors where our power comes in to another building to offset the large motor loads we have there. I'm not sure how that is monitored in this other building, but there must be a way. I'll ask about that and see what my boss says.  Regards, Ballpeen.

RE: Hot water heater argument

If you are using large industrial; water heaters this will probably not apply, but for residential heaters there are typically two elements each rated at the rating of the water heater. The upper heater comes on first on a fixed thermostat. This warms the water in the upper 1/4  or less of the tank very quickly to give fast recovery. When the upper thermostat reaches it's set point, it transfers the current to the bottom element that heats the rest of the water. This is the element with the adjustable thermostat.
An indication of a failled lower element is hot water available quickly but it runs out quickly.
respectfully

RE: Hot water heater argument

Waross,
could you post a link to the site regarding sterling cycle devices, please?
(Sorry for the unintentional thread-hijack folks...)


Kind regards,

Rob

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

RE: Hot water heater argument

Thanks Waross

Very interesting read.

Rob

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

RE: Hot water heater argument

its pretty simple

Either you heat the water or you don't

takes same energy to heat the water up 20 C no matter
what the source.

RE: Hot water heater argument

"...no matter what the source."

Some sources are cheaper than others. Also, a given source might be cheaper depending on when you use it.

So, it's not necessarily a matter of saving energy; it's a matter of saving money.

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