Water Heaters: Electricity Consumption

[jvanasin]

I am currently deciding between installing a centralised heater tank or tank-less heating units for

home/residential use.

Does anyone know which one is more cost-effective, from a purely electricity consumption perspective?

I know that that tank-less units are a pain when it comes to controlling the temperature but will

a lower electricity bill make up for this disadvantage?

Any comments will be greatly appreciated.

[Crossy]

Put simply the storage type will use slightly more electricity, because:-

1. There will always be some leakage of heat from the tank which required re-heating every now and then.
   
2. Unless the tank is right next to the point of use some hot water will be wasted when you run the tap waiting for warm water.
   

BUT

Instant heaters take a LOT of power which could put a strain on your (typically minuscule) power supply arrangements.

I would consider small (5-8kW) instant heaters at point of use and a solar pre-heat (we have a 3.5kW unit that produces a trickle of lukewarm water ).

If you get the decent electronically controlled units keeping constant water temperature become a non-issue.

If you go for a tank type, consider putting it on a timer so it only tops up the heat in the morning (for your shower) and in the late afternoon (for dishes and your evening shower).

Edited March 16, 2009 by Crossy

[KritsakornWilson]

What about FREE HOT WATER ?

You don't have to worry about the electricity consumption at all. I am talking about heat recovery where the waste heat from the air-con is reclaimed or recovered and kept in a small storage tank which will give you free hot water for your baths, showers, jacuzzis, kitchen, dishwashers, washing machine, etc.

The beauty is that the system also reduces your air-con electricity usage by approx. 25% average.

Wanna know more about this, just call Wilson at 083-7672886

Oh, did I mentioned 5 years warranty? It also extends the warranty of your air-con unit.

So start saving energy, saving money and save the earth as well.

[KritsakornWilson]

What about FREE HOT WATER ?

You don't have to worry about the electricity consumption at all. I am talking about heat recovery where the waste heat from the air-con is reclaimed or recovered and kept in a small storage tank which will give you free hot water for your baths, showers, jacuzzis, kitchen, dishwashers, washing machine, etc.

The beauty is that the system also reduces your air-con electricity usage by approx. 25% average.

Wanna know more about this, just call Wilson at 083-7672886

Oh, did I mentioned 5 years warranty? It also extends the warranty of your air-con unit.

So start saving energy, saving money and save the earth as well.

The heat recovery system can reap more than 60 degree celsious and kept in the insulated storage tank with a loss of 3 degree each day, so if the air-con is not running for 3 days you will still have hot shower for the entire family for 4 days assuming you have a 200 liters hot water tank.

Optional sizes from 50 liters to 500 liters available.

Worth considering, FREE HOT WATER.

The local hotels are installing these babies to cut all their boilers running costs.

[Crossy]

What about FREE HOT WATER ?

Are you selling these in Thailand? Webpage?

Approximate prices would be good.

Are they a retro-fit to an existing aircon?

Whilst there is no doubt that these waste-heat recovery units work well but I fail to understand how they reduce the A/C power consumption. Please explain

[KritsakornWilson]

What about FREE HOT WATER ?

Are you selling these in Thailand? Webpage?

Approximate prices would be good.

Are they a retro-fit to an existing aircon?

Whilst there is no doubt that these waste-heat recovery units work well but I fail to understand how they reduce the A/C power consumption. Please explain

OK, These can be retro-fitted to an existing air-con as well as new ones, or you can have a new air-con system which is water cooled, instead of the conventional air cooled condensors.

Conventional A/Cs run a motor to blow the hot air off the condensing fins on the CDU outdoor unit, what we called an air-cooled system.

In the process of heat recovery, the high pressure hot energy from the compressor is channeled to the water tank via heat exchangers thus increase the efficiency of the condensor which will boost your fan-coil to cool down the room temp. quicker making the compressor rest more often thus reduce the energy required to run the A/C unit and the additional savings would be from the more rest the fan motor has throughout the entire running time of the A/C as you now have a cooler gas flowing through the condensing fins as most of the heat is transfered off into water before flowing to the fins.

Bear in mind, water is a better conductor than air.

Blow at your cup of hot coffee it will take you a longer time to cool the coffee than to just sit your cup in a bowl of water. So you see now water is a better heat conductor.

Systems like these starts from THB 10,000 upwards.

Feel free to call me.

[hhgz]

"water is a better heat conductor."

The efficiency of the heat transfer to water decreases as the heat of the water increases.

[jvanasin]

Put simply the storage type will use slightly more electricity, because:-

1. There will always be some leakage of heat from the tank which required re-heating every now and then.
   
2. Unless the tank is right next to the point of use some hot water will be wasted when you run the tap waiting for warm water.
   

BUT

Instant heaters take a LOT of power which could put a strain on your (typically minuscule) power supply arrangements.

I would consider small (5-8kW) instant heaters at point of use and a solar pre-heat (we have a 3.5kW unit that produces a trickle of lukewarm water ).

If you get the decent electronically controlled units keeping constant water temperature become a non-issue.

If you go for a tank type, consider putting it on a timer so it only tops up the heat in the morning (for your shower) and in the late afternoon (for dishes and your evening shower).

Thanks... I also reckoned tank-less (instant) heaters should be more energy-efficient since we do not use that much

warm water here in Thailand anyway...

[KritsakornWilson]

"water is a better heat conductor."

The efficiency of the heat transfer to water decreases as the heat of the water increases.

You mean water in a contained and constant stage, as in a closed storage tank.

It is subjective to whether the heated up water is being drained out to use and fresh cool water is being refilled into the storage tank, as in a normal household usage senario when you use the hot water the fresh cool water will flow into the storage thus the efficiency is still good, agreed?

In the instance of not using any hot water the waste heat from the A/C still flows to the condensing fins of the CDU as per normal function of the condensor.

The whole concept of heat recovery here is to produce the required hot water for daily usage without having to increase energy consumption i.e. electrical heaters, gas burners, etc.

Thus, free hot water from heat recovery systems saves money, saves energy and saves the planet.

[jvanasin]

What about FREE HOT WATER ?

You don't have to worry about the electricity consumption at all.

Yes, I have heard of these systems before...

I need warm water for 8 points (4 bathrooms with shower+basin in each bathroom), how many litres storage

would I need? How many air-con compressors would I need to connect to the system in order to maintain

a water temperature that is sufficiently warm for showers?

Thanks

[trogers]

Heat recovery system assumes you will use the air-conditioner(s) often. If not, water will not be heated up.

It is a safe assumption for hotels and the likes, but may not for a home.

If I usually turn on the air-con for 9 hours for sleep during the warm weather, I may get hot water for a shower in the morning, but this water will cool by the time I get home in the evening.

During the rainy or cool weather, I probably do not turn on any air-con. What then?

[InterestedObserver]

All else being equal, the heater with the smaller KW rating will cost less to operate.

[KritsakornWilson]

Heat recovery system assumes you will use the air-conditioner(s) often. If not, water will not be heated up.

It is a safe assumption for hotels and the likes, but may not for a home.

If I usually turn on the air-con for 9 hours for sleep during the warm weather, I may get hot water for a shower in the morning, but this water will cool by the time I get home in the evening.

During the rainy or cool weather, I probably do not turn on any air-con. What then?

Thanks for reminding me of these critical points,...

1stly, the A/C can be switched on at any intervals any period and any duration.

when the compressor kicks in, hot water will be produced and the storage will gradually get warm

till it reaches the perset temp of 60 degrees C. Assuming a 100 liters tank requires a 12,000BTU

A/C unit to run 4 hours to heat from 28 degrees C till the 60 degrees C point. Is this too fast....

.... Thank to modern material and heat transfer technology,its proven today.

2ndly, the water temp will drop 3 degrees C in a period of approx 12 hours in an 2 inches PP foam

insullated tank, thus, in the event that your A/C is not running for the weekends when you are

away, you will still have a hot shower at more than 40 degrees C.

..... Many thanks to modern material and heat insullation technology.

3rdly, During cool season or rainy days for more than 3 days period I would suggest :

A) Switch on the A/C for 1 hour daily to maintain the hot water in the tank, or...

Add on an electrical heating rod into the tank for these cool times only.

Object here is to reduce energy consumption and saves money on bills.

Nevertheless, I am sure there are plenty of room still for improvements.

Thanks guys.

[Gary A]

Scavenging heat from an air conditioning condenser is a great idea. Unfortunately my electric bill would be MUCH higher because I seldom use the air conditioning. Running the air conditioner just for the hot water would be a quite counter productive.

As far as tank type versus on demand, the tank type is about the same price, requires less wiring and will last a lot longer. The secret is to buy the best quality tank type heater that you can find. A well insulated tank will lose less than two degrees heat per hour. Replacing a heating element is easy and cheap to do. A hundred liter tank type will draw normally less than 4,000 watts with both elements on high. My on demand hot water shower is 5,500 watts and during cold weather I have to drastically reduce the flow to have even warm water. For that reason alone, my next water heater will be a tank type.

[johnnyk]

Scavenging heat from an air conditioning condenser is a great idea. Unfortunately my electric bill would be MUCH higher because I seldom use the air conditioning. Running the air conditioner just for the hot water would be a quite counter productive.

As far as tank type versus on demand, the tank type is about the same price, requires less wiring and will last a lot longer. The secret is to buy the best quality tank type heater that you can find. A well insulated tank will lose less than two degrees heat per hour. Replacing a heating element is easy and cheap to do. A hundred liter tank type will draw normally less than 4,000 watts with both elements on high. My on demand hot water shower is 5,500 watts and during cold weather I have to drastically reduce the flow to have even warm water. For that reason alone, my next water heater will be a tank type.

Gary, Using 5500W for 10 mins. doesn't seem bad to me and I like that I don't ever have to wait for the tank to re-heat. And I like that I don't have to allocate or find space for a tank.

I'm not good at this so how much wattage do you estimate it takes to keep the tank water warm enough for a shower?

[Crossy]

I'm not good at this so how much wattage do you estimate it takes to keep the tank water warm enough for a shower?

A VERY rough guesstimate would suggest that a 100 Litre, 2" foam insulated tank would lose about 30Watts, converting to electrical units thats about 1 unit in 36hours.

Add to that the power used to re-heat the water used (same as an on-demand heater would use for the same amount of water).

Edited March 19, 2009 by Crossy

[KritsakornWilson]

Ok guys, no doubt about it, I am encouraging the Heat Recovery Systems because I just set up a showroom in Pattaya to promote energy saving solutions to the local hospitality industry.

The heat recovery system is basically reclaiming the waste heat in any given system and reused for energy saving purpose. The word here is 'System' thus its more complicated than just an instant heater with or without storage tank stand alone installation.

If your hot water usage is just 10 minutes of warm shower requirement daily, then there is no need to opt for a 'system' but just a stand alone installation.

But if your usage of hot water is greater then mentioned, and/or your concern is to save energy (i.e. saves energy to make hot water all together and saves energy of the running A/C.) then we shall discuss further for the benefits of everyone.

Oh, before I forgot, I did mentioned that we could drop in a heating rod into the storage tank so in the event that you do not wish to switch on the A/C for many days you may still heat up the water in the storage tank conventionally with the options of 1000 watts to 4500 watts glass heating rods which is 100% safe as compared to other heating rods which are made of steel, copper or stainless steel.

This is not a threat, but a true incident in a hotel in Pattaya (names kept on purpose) an electric heater blown up due to the hard water condition in Pattaya (known fact) because calcium scale built-up on the entire surface of the stainless steel heating rod reduced the heat transfer efficiency from the heater surface to water body, thus the heater will be turned to the fullest power and caused the heating element to increase its temperature inside the stainless steel rod eventually exploded like a pressure cooker. So I only install a glass rod heater whenever required to eliminate this risk all together.

( You can imaging when the heater exploded and the life wire get in contact with running water and the guy is having his shower at that time...... )

[lopburi3]

"I know that that tank-less units are a pain when it comes to controlling the temperature"

Am not sure how you know that as my experience is exactly the opposite. Point of use heaters provide a steady temperature. Water tanks are subject to mix valve and line run variables. That may be less there than in a sub zero country but they can change from cold to scalding even here - you do not have that issue with point of use as you set the temperature you want and only a huge change in pressure will change it more than a few degrees (manual type). Many have automatic control if that is too much. It also only requires one water run. And for most people who use the hand shower your only use the water for several minutes - you turn off flow while washing - so the electric use is marginal - and except in cold season never full power rating of the unit.

[Crossy]

"I know that that tank-less units are a pain when it comes to controlling the temperature"

Am not sure how you know that as my experience is exactly the opposite. Point of use heaters provide a steady temperature.

The issue with 'instant' heaters is that the simple (cheap) ones have no thermostat (just an overheat preventer) so the water temperature is dependent upon flow rate, less flow=hotter water.

The better units have an electronic controller which accurately regulates the output temperature.

[lopburi3]

That must be bottom round (or some made in Europe) as every Japaneses units I have bought (in the 3k baht range), more than ten over the years, has had a control. The cheap units just a reostate but the more expensive units digital display/setting. Actually I prefer the simple knob of the reostate myself. Much easier than getting hot/cold taps to keep a temperature setting in my experience.

[KritsakornWilson]

That must be bottom round (or some made in Europe) as every Japaneses units I have bought (in the 3k baht range), more than ten over the years, has had a control. The cheap units just a reostate but the more expensive units digital display/setting. Actually I prefer the simple knob of the reostate myself. Much easier than getting hot/cold taps to keep a temperature setting in my experience.

Just for your info, the Hot/Cold mixer taps now comes with mix ratio lock to set your desired temperature everytime you decide to flick the tap on. Scalding and loss of hot water when more than 2 person takes a shower and a bath is a common complaint, fact is a fact, wouldn't want to argue with that.

If you are comfortable with your instant heater and do not wish to make any changes to keep up with the modern times and technology, well, the choices and decision is all up to you.

Just wanna add, all modern technology and engineering is for the betterment of us all, we make our own choice to accept it or not, nevertheless, life still goes on.

I remembered the days when my grandmother would have to boil hot water in a kettle to mix a tub of warm water to wash me in the morning......that was the love I missed since God rest her soul 13 years ago.

Good luck to you guys, was fun to share info like these, by the way, its my first time on the forum.

See ya.

[Gary A]

"I know that that tank-less units are a pain when it comes to controlling the temperature"

Am not sure how you know that as my experience is exactly the opposite. Point of use heaters provide a steady temperature. Water tanks are subject to mix valve and line run variables. That may be less there than in a sub zero country but they can change from cold to scalding even here - you do not have that issue with point of use as you set the temperature you want and only a huge change in pressure will change it more than a few degrees (manual type). Many have automatic control if that is too much. It also only requires one water run. And for most people who use the hand shower your only use the water for several minutes - you turn off flow while washing - so the electric use is marginal - and except in cold season never full power rating of the unit.

A single point use such as a hot water shower does a great job maintaining temperature. A friend of mine has a high powered unit that is used for several points. That's where the major problem is. It provides VERY hot water and is not adjustable. It would seem like simple mixer faucets would work fine. The fact is that they don't. You get the temperature just right, get in the shower and all of a sudden it just turns cold. You fiddle with the faucets and you have to quickly jump out to avoid getting scalded. I told him that I think the problem is that the multi point unit is too powerful and when you mix enough cold water to it to be comfortable, the cold water back feeds into the heater and either the unit's pressure switch or the overtemp safety shut it down resulting in no hot water. Whatever the reason, neither him nor I are smart enough to fix the problem. If the multi point unit were adjustable, I think it would work much better.

That powerful unit needs a certain amount of water flowing through it to work properly. I can turn the hot water to the sink while taking a shower and everything works fine. That is an expensive way to shower. A waste of water and electricity.

[stgrhe]

"I know that that tank-less units are a pain when it comes to controlling the temperature"

Am not sure how you know that as my experience is exactly the opposite. Point of use heaters provide a steady temperature. Water tanks are subject to mix valve and line run variables. That may be less there than in a sub zero country but they can change from cold to scalding even here - you do not have that issue with point of use as you set the temperature you want and only a huge change in pressure will change it more than a few degrees (manual type). Many have automatic control if that is too much. It also only requires one water run. And for most people who use the hand shower your only use the water for several minutes - you turn off flow while washing - so the electric use is marginal - and except in cold season never full power rating of the unit.

A single point use such as a hot water shower does a great job maintaining temperature. A friend of mine has a high powered unit that is used for several points. That's where the major problem is. It provides VERY hot water and is not adjustable. It would seem like simple mixer faucets would work fine. The fact is that they don't. You get the temperature just right, get in the shower and all of a sudden it just turns cold. You fiddle with the faucets and you have to quickly jump out to avoid getting scalded. I told him that I think the problem is that the multi point unit is too powerful and when you mix enough cold water to it to be comfortable, the cold water back feeds into the heater and either the unit's pressure switch or the overtemp safety shut it down resulting in no hot water. Whatever the reason, neither him nor I are smart enough to fix the problem. If the multi point unit were adjustable, I think it would work much better.

That powerful unit needs a certain amount of water flowing through it to work properly. I can turn the hot water to the sink while taking a shower and everything works fine. That is an expensive way to shower. A waste of water and electricity.

The problem you refer to is because the water pressure changes. The first one needs to do is to have at least some kind of pressure regulator in the loop since the mixers cannot adjust to large variation in the water pressure. To improve it further one should select mixers that also do adjust for minor variations in the water pressure in addition to regulating the temperature. A standard mixer simply cannot do the job of mixing hot and cold water comfortably.

[rjhklein]

Hi Wilson, seems like your number is outdated, can you please send me a new one.

Regards

What about FREE HOT WATER ?

You don't have to worry about the electricity consumption at all. I am talking about heat recovery where the waste heat from the air-con is reclaimed or recovered and kept in a small storage tank which will give you free hot water for your baths, showers, jacuzzis, kitchen, dishwashers, washing machine, etc.

The beauty is that the system also reduces your air-con electricity usage by approx. 25% average.

Wanna know more about this, just call Wilson at 083-7672886

Oh, did I mentioned 5 years warranty? It also extends the warranty of your air-con unit.

So start saving energy, saving money and save the earth as well.

[bangkokumpalumpa]

hmmmm all this is fine but lets get real people GO SOLAR!!!!

when you look at water heating and the cost it is better to look at a solar system, one install cost and then free hotwater!

ok they are not cheap to buy, but hey when you think of what you get in return then they are great!!!!

when looking at a system dont be cheap, buy a good one and you will have hot water all year round!

no I am not selling solar system, I just know with the sun we have here in thailand verse NZ solar is a lot better way to go than paying the power company money, and after all they get some of there energy from the solar farms that they have built!!!

[longball53098]

It costs me about 4400 baht a year to operate my 6,000 watt instant hot water heater. This is figured on using the heater for about 30 minutes a day. We (two of us) don't normally use the heater that much but it takes in to account the kitchen heater for dishes. So roughly in 10 years I spend about 44k baht for electrons to run my heater.

How does that stack up to paying once for a solar system?

[rjhklein]

About the controling of temperature... There is now a new unit of STIEBEL ELTRON and you can get it at the Home Pro.

It can regulate the temparature much more precise. Have look..

http://www.stiebeleltronasia.com/showprodu...ductseriesid=76

I am currently deciding between installing a centralised heater tank or tank-less heating units for

home/residential use.

Does anyone know which one is more cost-effective, from a purely electricity consumption perspective?

I know that that tank-less units are a pain when it comes to controlling the temperature but will

a lower electricity bill make up for this disadvantage?

Any comments will be greatly appreciated.

[Sheryl]

In terms of electricty cost it depends what type of tank you are comparing the tank-less to and how you will use it. The large tanks that are on all the time will use more power than a tank-less unit. However the small ("mini storage tanks") units may be less, especially if you turn it off when it will not be needed for a while.

If you only want to shower, this is pretty easy as that is what most of the water heaters sold here are designed for. But if you or anyone in your family likes to take baths, need to carefully consider what you buy as most of the the tank-less units do not give sufficient flow rate to fill up a bathtub befopre the water cools off. (As I learned too late..!) For that, need either a high flow tank-less (which I believe use a lot of electrricity) or a tank type.

Also with the tank-less types need to see about your water pressure as they have minimimum requirements in L/min to work well.

[tig28]

I am a fan of the instant heaters. Remember the cost savings of not needing copper piping for reticulation. Few locals are familiar with the correct techniques required to successfully install copper hot water pipe with decent connections and terminations --- although this somewhat depends on your location.

I also dislike "unnecessary" water piping running throughout my house. With perfect plumbing techniques this is a small concern but ...............

"I know that that tank-less units are a pain when it comes to controlling the temperature"

I do not find this at all ---- in fact quite the opposite !

Compared to my neighbor who uses a "whole house" heater ( and wishes he didn't ) my overall electricity costs are about 30% lower --- i believe (but can't prove) this is largely due to my 'point of service' hot water system.

Good luck with whatever you choose.

[SantiSuk]

I have one of each (the builder decided to put in two systems to cover two halves of the house). I am sure the tankless jobbie is cheaper, but that's not much compensation for having an unreliable heater. 10% of the time it delivers good falang shower temperatures and water for the kitchen sink. 50% of the time it is acceptably warm and 40% of the time it is unacceptably lukewarm, It's a German Steibel and the problem is the variable (low) power in an Issaan village, not the heater.

Useful thread - I'll go for a properly engineered mixed recovery/solar/power booster system next time if I can find a good heating engineer