36kw tankless water heater

[Hv&Lv]

Make sure the power utility co is aware of your plans. They are not very fond of electric tank h20 heaters here.

Great Point!!
it isn’t that we aren’t fond of them, we just need to know to upsize the transformer.
anything that increases kWh sales are good...
nothing worse than a transformer tripping out at 6 AM with the water heater pulling 150 amps and the 10kW strip heat on when it’s 25 degrees outside.

 

[kwired]

Great Point!!
it isn’t that we aren’t fond of them, we just need to know to upsize the transformer.
anything that increases kWh sales are good...
nothing worse than a transformer tripping out at 6 AM with the water heater pulling 150 amps and the 10kW strip heat on when it’s 25 degrees outside.

But it is supposedly not going to increase kWh sales and the reason to use an on demand water heater. It possibly requires higher capacity equipment to supply the demand when needed though, and if there is no construction charges or demand charges ends up being a net loss to some degree to the POCO to supply such things.

 

[kwired]

Have another question(Sorry if its a Dumb question). It's pertaining to this job so I don't want to make a new post. According to 376.56(B)(1) Distribution blocks shall be marked "Suitable for use on the line side of service Equipment" or equivalent.

So when working on my bid last night, I could not find a Block that had that marking. Called my supply house and then NSI and they kind of did not know what I wanted.
The block I wanted has an SCCR rating, would that qualify as "Equivalent" According to 376.56.(B)(1) (I don't think it would)
Tried doing a General look around google but no luck.

Attached is the Block I was looking at http://www.nsiindustries.com/catalog...locks/al-r2-m4

Problem I see here without looking back on ROP's is it is not obvious what the intent was -

It seems to only apply to 376 and not to similar situations in 312, 314 or even anywhere in art 230 for that matter - so why only metal wireways? and what do they consider to be a distribution block? There are blocks on insulated assemblies that you mount in an enclosure or wireway, there is what many call "polaris taps" though there are others out there making similar connectors that do not have mounting means and you just land conductors in them. There is also ways to make up things in similar appliactions with crimped on connecting devices.

Might have to look at listing standards to determine what actually is a distribution block? If not using such item does it still need to comply, or is only thing you can use need to be a listed distribution block, but only if in a metal wireway?:?

 

[Hv&Lv]

But it is supposedly not going to increase kWh sales and the reason to use an on demand water heater. It possibly requires higher capacity equipment to supply the demand when needed though, and if there is no construction charges or demand charges ends up being a net loss to some degree to the POCO to supply such things.

We have them on our system now...
I fail to see your reasoning on how they will not be an increase in kWh sales...
I can show you customers bills before and after these installs.
some have went as far as reinstalling a tank water heater.
its proven in the industry these high kW units aren’t money savers

 

[kwired]

We have them on our system now...
I fail to see your reasoning on how they will not be an increase in kWh sales...
I can show you customers bills before and after these installs.
some have went as far as reinstalling a tank water heater.
its proven in the industry these high kW units aren’t money savers

The concept of why you use a tankless heater is that it only heats water while there is demand for the water. It takes same energy to raise a gallon of 60 degree water to 120 degrees whether it is done in a tank or during the time it passes through the tankless unit. The efficiency of the unit should be higher than a tank type heater, that don't mean you don't get higher energy rates, demand charges, etc. because of the nature of your loading, but actual kWh needed to use a specific amount of hot water at specific temp should be less.

The tank style unit has losses during storage, and must periodically replenish those losses. If the tankless is using more energy then you probably have other loss reasons or they actually are using more hot water for some reason in those instances.

Sometimes when people get something that is supposed to be energy efficient they tend to make poor decisions in using it because they think it is more efficient they can get away with those poor decisions.

 

[winnie]

I have a tankless gas water heater. I love it. Subsidized because it uses less gas per gallon of hot water delivered, but I love it because there no longer is a limit on the gallons I use

I still end up saving money because I converted from an electric storage heater to a gas tankless...

A 400A service to a 1200 sq foot house seems like severe overkill to me, but heating water takes lots of energy, and if you want to enable 3 separate users at once (dishwasher, laundry, tub) then you have lots of flow....

-Jon

 

[kwired]

I have a tankless gas water heater. I love it. Subsidized because it uses less gas per gallon of hot water delivered, but I love it because there no longer is a limit on the gallons I use

I still end up saving money because I converted from an electric storage heater to a gas tankless...

A 400A service to a 1200 sq foot house seems like severe overkill to me, but heating water takes lots of energy, and if you want to enable 3 separate users at once (dishwasher, laundry, tub) then you have lots of flow....

-Jon

But it takes same energy to heat same amount of water by the same number of degrees. The 400 amp service becomes necessary because with the instant heater you are trying to do the work in a lesser time, but are not using any energy to maintain a storage tank during non use periods.

Same for the gas unit, it will use approximately same amount of gas to heat same amount of water the same temp. Efficiency isn't 100% like it is for electric heat source so losses will vary a little but will still be in same ballpark if both have similar efficiency rating.

It just happens to be easier to deliver the higher energy rate with gas without increasing the cost of what is needed to deliver it at that rate. Chances are you run same size gas pipe to tankless as you do to the tank type unit, but electric units the tank type are typically slower recovery at a lower input rate. You could put 36kW of heating elements in a 50 gallon tank and have faster recovery, should still use right about the same energy if water usage remains the same. But along with that still comes the need to be able to supply higher demand in short time vs lower demand over longer time which means larger source, conductors, gear ... maybe demand charges or different rates because of the situation of more cost involved to deliver similar amount of energy.

If it cost less to operate than the old electric unit (energy only not the additional equipment and possible demand fees) then it is because your gas cost less per unit of heat than electric and not so much because it is any more efficient at transferring that energy, in fact the gas unit is probably less than 100% efficient because some of the heat leaves the exhaust flue where the electric unit doesn't have that loss.

 

[growler]

A 400A service to a 1200 sq foot house seems like severe overkill to me, but heating water takes lots of energy, and if you want to enable 3 separate users at once (dishwasher, laundry, tub) then you have lots of flow....

-Jon

I know where there is small house that's out in the country that is only about 1500 sq ft ranch style house that has a 400 amp service. The house was built in the early 1960s so this really perplexed me (original service ). They just didn't install services that big on small houses back in those days. They didn't even do a lot of indoor pot growing at the time.

After a few trips to the house to do upgrades and repairs I ask the owner why on earth they had such a large service when it obviously wasn't needed. Turns out they had a very reasonable explanation . The house was owned by the customer's father that planned to open a cabinet shop out back when he retired and would be using some large wood working equipment. He got as far as having the foundations poured ( more than one building) and then he died and the project was canceled. All this happened back in the 60s and the house still has a 400 amp service.

Just thought it's interesting the things you run into from time to time.

 

[Stebs]

But it takes same energy to heat same amount of water by the same number of degrees. The 400 amp service becomes necessary because with the instant heater you are trying to do the work in a lesser time, but are not using any energy to maintain a storage tank during non use periods.

Same for the gas unit, it will use approximately same amount of gas to heat same amount of water the same temp. Efficiency isn't 100% like it is for electric heat source so losses will vary a little but will still be in same ballpark if both have similar efficiency rating.

It just happens to be easier to deliver the higher energy rate with gas without increasing the cost of what is needed to deliver it at that rate. Chances are you run same size gas pipe to tankless as you do to the tank type unit, but electric units the tank type are typically slower recovery at a lower input rate. You could put 36kW of heating elements in a 50 gallon tank and have faster recovery, should still use right about the same energy if water usage remains the same. But along with that still comes the need to be able to supply higher demand in short time vs lower demand over longer time which means larger source, conductors, gear ... maybe demand charges or different rates because of the situation of more cost involved to deliver similar amount of energy.

If it cost less to operate than the old electric unit (energy only not the additional equipment and possible demand fees) then it is because your gas cost less per unit of heat than electric and not so much because it is any more efficient at transferring that energy, in fact the gas unit is probably less than 100% efficient because some of the heat leaves the exhaust flue where the electric unit doesn't have that loss.

Here where I am in Kansas, natural gas is about 1/3 the cost of electricity for the same amount of heat. I went large tankless this spring and can tell you this. Tankless took a bigger gas line than the tank, and only draws about 80 watts when running. Exhaust is via 2” pvc and is barely warmer than ambient temp, and not much exhaust flow at that. It also takes up less floor space than a tank.

One other thing the op should look into here is possible demand charges. I’m on a demand meter, and 36kw would add $324 to the bill if ran wide open for an hour in the summer. Wouldn’t take many months of that to offset the cost of going to gas, especially by the time you figure in the cost of all that wiring to support 36kw. 36kw would also rule out any future for having hot water on a residential standby generator if they ever decided to put one in.

 

[kwired]

Here where I am in Kansas, natural gas is about 1/3 the cost of electricity for the same amount of heat. I went large tankless this spring and can tell you this. Tankless took a bigger gas line than the tank, and only draws about 80 watts when running. Exhaust is via 2” pvc and is barely warmer than ambient temp, and not much exhaust flow at that. It also takes up less floor space than a tank.

One other thing the op should look into here is possible demand charges. I’m on a demand meter, and 36kw would add $324 to the bill if ran wide open for an hour in the summer. Wouldn’t take many months of that to offset the cost of going to gas, especially by the time you figure in the cost of all that wiring to support 36kw. 36kw would also rule out any future for having hot water on a residential standby generator if they ever decided to put one in.

Barely warmer than ambient temp on the exhaust is still an inefficiency, but like you said cost per unit of heat is less for you with gas than it is with electric resistance heating. Probably is for many but not necessarily all. Your 80 watts when running is the combustion air fan, that is one more cost that though somewhat insignificant isn't even included in the overall cost of operating that appliance, most just look at the cost of gas.

It likely still uses less gas than a storage tank heater that is heated by gas - presuming you used same amounts of hot water, this because you had less losses during the non use periods that the storage tank was losing. I have said many times before and maybe even earlier in this thread, that loss may not be as big as you think depending on circumstances. If you have longer heating vs cooling season, that lost heat goes into your home, unless the tank is not in your home, and does lessen the heating load, but it also will increase cooling load so if you have long cooling seasons it may be less desirable than if you have long heating seasons.

And yes demand charges if they are applied will make the electric version cost more to have than a typical storage tank type that don't put you into high demands, but that is a cost thing and not an energy efficiency thing. Energy used is still typically going to be less on tankless than on tank type regardless of gas or electric - both only heat when there is a demand for water rather than maintaining temp in a tank whether there is any hot water demand or not.

 

[winnie]

Yes, sorry for being cryptic. I recognize that a tankless is subsidized because of efficiency, but _I_ love the unlimited hot water.

I recognize that using gas or electric resistance requires similar energy input for the same hot water output, but that natural gas is cheaper than electricity.

So I am using _more_ hot water and thus more BTU of energy because of the tankless, but saving money because I switched from electric to gas.

Still to enter this discussion is the use of heat pump electric storage water heaters.

 

[junkhound]

Still to enter this discussion is the use of heat pump electric storage water heaters.

We have a 55 gal heat pump WH at home. Just wife and self nowadays, no long showers by personal preference, only run dishwasher ever 3rd day or so..
Have a separate meter on HPWH. Approx 11 cents kW-hr rate on PSE>. Also, laundry done in cold water.

4 years old in Sept, did install R-19 blanket around the tank. Installed in 60F basement. 4 years ago PSE paid $700 toward a HPWH.

TOTAL useage for 4 years and one month of 1723 kW-hrs, that is about $3.87 a month for hot water. Problem free GE brand. .
Probably 10% or more of bill was likely grandson and or granddaughter living here for one school year, liked 40 minute showers, about the limit of the HPHWH. We would run the dishwasher at the same time to shorten shower times considerably:lol:.

 

[kwired]

Yes, sorry for being cryptic. I recognize that a tankless is subsidized because of efficiency, but _I_ love the unlimited hot water.

I recognize that using gas or electric resistance requires similar energy input for the same hot water output, but that natural gas is cheaper than electricity.

So I am using _more_ hot water and thus more BTU of energy because of the tankless, but saving money because I switched from electric to gas.

Still to enter this discussion is the use of heat pump electric storage water heaters.

The heat pump opens a different can of worms. In that instance you are using energy to transfer heat that is already existing someplace else instead of using energy to directly heat the water.

You must also consider where that existing heat is coming from and what it may be costing you in other ways. If that heat is from inside your home, the HPWH is helping your cooling system by taking heat out of your home. So you are not only making hot water but also cooling your home at same time. But same system is robbing your heating system in the heating season - so it will have to work harder. If the heating system is resistance heat - you probably just as well off using resistance heat for water heating also whether it be tank or tankless system and save on upfront cost of the heat pump - unless you are in the south and your cooling season is much longer than the heating season.

 

[cpickett]

We have them on our system now...
I fail to see your reasoning on how they will not be an increase in kWh sales...
I can show you customers bills before and after these installs.
some have went as far as reinstalling a tank water heater.
its proven in the industry these high kW units aren’t money savers

Even if the total kWh for tank vs tankless is the same, doesn't a tankless impact the grid negatively in that you have short periods of time with 36kW demand vs. longer periods of time with 3kW demand? When the tankless calls for heat you have to supply the full 36kW and when it shuts off you have to dump that capacity.

 

[kwired]

Even if the total kWh for tank vs tankless is the same, doesn't a tankless impact the grid negatively in that you have short periods of time with 36kW demand vs. longer periods of time with 3kW demand? When the tankless calls for heat you have to supply the full 36kW and when it shuts off you have to dump that capacity.

Yes, but 36kW is a small load when looking at it from grid perspective. Now if you have a large percentage of customers served with a similar non continuous loads of same magnitude it can start to become an issue, and a situation that possibly can be financially offset by demand metering and charges.

With a steam boiler as the driving force for the generator, you basically need to have enough steam ready to take on the sudden demand, so long as there isn't too much sudden damand all at one time they typically can ride through it, as they probably have steam at a high enough level to take on a certain amount of sudden demand as normal operating procedure anyway. Known demand increases, a factory on the system typically starts to increase load at same time every day - is easy to account for. Even general added load for air conditioning or just a general increase on workdays at a particular time frame - is for the most part predictable enough they are ready for it. Of course all those people that went to work at about the same time stopped using extra energy at home when they left to go to work.

 

[GeorgeB]

Yes, but 36kW is a small load when looking at it from grid perspective.

I see quite a few pole mounted with "25" on them supplying 2 or 3 homes ... the 36kW is a big piece <g> of that 25kVA if that's what the 25 means.

 

[kwired]

I see quite a few pole mounted with "25" on them supplying 2 or 3 homes ... the 36kW is a big piece <g> of that 25kVA if that's what the 25 means.

It is a big load on an individual 25 kVA transformer serving the customer, it is a drop in a huge barrel to the substations and generation plants.

 

[Ravenvalor]

Great Point!!
it isn’t that we aren’t fond of them, we just need to know to upsize the transformer.
anything that increases kWh sales are good...
nothing worse than a transformer tripping out at 6 AM with the water heater pulling 150 amps and the 10kW strip heat on when it’s 25 degrees outside.

I have heard a story of a local utility company having to go into suburban neighborhood and replacing their underground lines after practically everyone in the neighborhood decided to install electric tankless water heaters.

Also, my neighbor installed one in his home and the utility company tried to charge him for replacing his transformer.