Heating water beyond 65'C

[desA]

A few technologies seem to be emerging which claim to be able to heat water to around 80'C, using heat-pump technology.

A few questions:
1. In what applications would such high water temperatures be useful?
2. Are the economics feasible for these kinds of machines?
3. Would these be commercial, or domestic applications?
4. What system difficulties could occur over the equipment lifetime?

[NoNickName]

1) sterilisation of water used for cleaning sensitive environments, like surgical theaters, and drip pans of AHUs to avoid formation of legionnaire's colonies.
2) CO2 units seem to have the best performance in these regards. They only appear to be economically feasible when heating is recovered.
3) Both. In Japan, they are used to heat water for old heating systems with iron thermosyphons.
4) Wear and tear of heat pumps, which is generally more expensive then boilers and burners.

[desA]

Many thanks NoNickName. Much obliged.


1) sterilisation of water used for cleaning sensitive environments, like surgical theaters, and drip pans of AHUs to avoid formation of legionnaire's colonies.

What is the typical range of temperatures required for this? I've read articles referring to 65'C as being adequate to deal with Legionnaires, for instance.


2) CO2 units seem to have the best performance in these regards. They only appear to be economically feasible when heating is recovered.

Can you perhaps elaborate further on the heat-recovery part?


3) Both. In Japan, they are used to heat water for old heating systems with iron thermosyphons.

Ok. Makes sense.


4) Wear and tear of heat pumps, which is generally more expensive then boilers and burners.

What is a typical major component expected lifetime for a ultra-high temperature heat-pump? Is 10-15 years unrealistic? How would this compare to a boiler, or gas burner?

[NoNickName]

Many thanks NoNickName. Much obliged.

You're welcome :D



What is the typical range of temperatures required for this? I've read articles referring to 65'C as being adequate to deal with Legionnaires, for instance.

The optimum temperature for growth is
around 37°C; at 46°C, the bacteria begin to die. 65°C or more is adequate.

There are numerous reports on the temperature-time
relationship required to kill Legionella. While there is no
definitive study, the following figures are provided as
background information:
• 71.7°C for 15 seconds causes 100 per cent kill
(Birkbeck 1993)
• 70°C causes 100 per cent rapid kill (AWT 2003)
• 70°C for 10 minutes eliminates Legionella from water
(EPA 1999)
• 61.7°C for at least 30 minutes causes 100 per cent kill
(Birkbeck 1993)
• 60°C for 2 minutes causes 90 per cent kill (AWT 2003)
• 60°C for 2.7 minutes causes 90 per cent
(Barbaree Unknown)
• 55°C for 27 minutes causes 90 per cent kill
(Barbaree Unknown)
• 50°C for 2 hours causes 90 per cent kill (AWT 2003).
These varying reports show that relying purely on heat
to disinfect a system colonised with Legionella may not
always be successful. The department advises that 71°C is
maintained at an outlet for five minutes.

http://health.vic.gov.au/environment/downloads/hs874_legion_warm_water_web.pdf



Can you perhaps elaborate further on the heat-recovery part?


Transcritical R744 systems are not as energy efficient as traditional AC equipment. If, on the other hand, it is equipped with a desuperheater or heat recovery, then the temperature level of it can be ideal for high temperature warm water systems, and thus being economically feasible.




What is a typical major component expected lifetime for a ultra-high temperature heat-pump? Is 10-15 years unrealistic? How would this compare to a boiler, or gas burner?

Compressor is the most stressed component, but the statistics do not go so much back in time for R744 systems to give us sufficient confidence. Anyway, I wouldn't expect a heat pump to survive against a boiler.

[Gary]

It seems to me there would be only a very few specialized commercial applications where the ability to kill off Legionella is needed.

Certainly this would not be needed in residential applications?

[chemi-cool]

Hi Des.

I want to enlighten the subject from a different angle.

I think that quantities of hot water in each location is an important point.

A heat pump is stationary and can not be carried around.
Not many places will invest in expensive machine that also need servicing once in a while.

So, I think that the target consumer is the No.1 Thing.

[desA]

Thanks again, NoNickName, for an excellent review of Legionnela & the temperatures required to combat it.

The Victoria article makes for good reading.

[desA]

It seems to me there would be only a very few specialized commercial applications where the ability to kill off Legionella is needed.

Certainly this would not be needed in residential applications?

Probably right. I'd thought of hospital requirements & perhaps applications where centralised cooling systems exist, with large pools of condensate, or water (not to mention mosquitoes etc).

I wonder if hospitals could use water close to the steam point for sterilisation of more active bugs than Legionella, for instance - if such things exist.

[desA]

Hi Des.

I want to enlighten the subject from a different angle.

I think that quantities of hot water in each location is an important point.

A heat pump is stationary and can not be carried around.
Not many places will invest in expensive machine that also need servicing once in a while.

So, I think that the target consumer is the No.1 Thing.

Some good thoughts - chemi.

What I had in mind was perhaps the replacement of steam-generation boilers by ultra-hot water heat-pumps. From both an energy & safety perspective. The cost of raising steam can be fairly onerous.

[Gary]

As water temp rises, heat pump performance decreases and wear and tear on the equipment increases... so from an energy savings viewpoint it would make sense to only raise the water temp to that which is needed for the application.

In a residential application, very hot water might only be needed for radiant heating... but this would only be needed during the winter, so perhaps it should be a separate system from domestic hot water for showers and such?

[desA]

As water temp rises, heat pump performance decreases and wear and tear on the equipment increases... so from an energy savings viewpoint it would make sense to only raise the water temp to that which is needed for the application.

Agreed.


In a residential application, very hot water might only be needed for radiant heating... but this would only be needed during the winter, so perhaps it should be a separate system from domestic hot water for showers and such?

What kind of temperatures would these radiant heaters need?

[Gary]

What kind of temperatures would these radiant heaters need?

Not much call for radiant heat here in Florida.

Perhaps others can answer this question. :)

[NoNickName]

Not much call for radiant heat here in Florida.

Perhaps others can answer this question. :)

Iron radiators 80°C, alu radiators 60/70°C

[desA]

What kind of water flowrates do these radiant heaters require?

[mad fridgie]

80C (79C) water is used for sterlisation and is required in many food processing/production plants. For example Dairy farms need 85C water to be stored, when used in the cleaning process drops to 80C, this temp is also required to break down milk fats. The process not need hot water, but can uses a a number of chemicals to achieve the same cleaning process.
These types of high temp heat pumps are designed to heat water to a variety of temperatures, not just the extremes above 80C.
As Chemi as stated all these type of energy saving products, depends upon load profile (how much energy/money are you saving)
Like any system that heats water to high temps "open loop" servicing is required " mineral deposits"
Efficiency depends upon many factors, these are specific to the application.
For example my units used in the food processing industry are generally running at 700% producing 87C water. This can be higher upto 1000%, but generally do not install is average is under 350% (unless client uses massive amounts of hot water)
Reliability, these machines are not priced at the bottom end and therefore tend to have excellent system protection.
Commercially I tend to look for clients whos simple payback is less than 3 years.
Install cost $15000, so need to save a minimum of $5000 per year, very occassinally you also get the ones who can save this amount in just over 6 months

[desA]

Thanks very much, MF.

So, essentially, water up to 85'C (storage), point-of-use ~ 80'C for sterilisation & milk-fat removal.

[NoNickName]

What kind of water flowrates do these radiant heaters require?

Depends on heating capacity. You may find the info on radiant heaters leaflets

[desA]

Thanks NoNickName.

If anyone perhaps has links to some of these radiant heater specifications, I'd be most grateful.

[chemi-cool]

I think that the term Radiant heaters refer to electric ones.

those you have in mind call Radiators.
Google for hot water radiators.

[Quality]

Try these manufacturers - Radson, Rettig, Barlow, Purmo, Stelrad for radiator info

[desA]

Thanks very much for the leads, Quality. Much obliged.