Heat pump solution

[fayeque]

Is heat pump a viable retrofit over Boiler to generate hot water for the use in places like hotel? the hot water temperature requirement is 60 deg Celcius. please let me know in casu you need more details. any comment on this will be highly appreciated..

Regards,
Fayeque

 

[Drazen]

for places like hotel detail engineering calculation and analysis is necessary to give proper direction.

doing without that is the same as if the doctor would prescribe medicament to patient without blood tests or other tests.

generally, heat pumps are not good in providing 60 degrees temperature, and magninute of hot water demand is high, they cannot work alone.

that does not mean, however, that combination of heat pump and smaller hot water boiler is not much more effective than hot water boiler alone. the judgment mostly depend on mentioned analysis. climatic area where you are in plays one of major roles.

 

[willard3]

Given that the Carnot cycle (heat pump) is less efficient than a boiler, start with fired water heating equipment.

 

[chicopee]

Interesting problem. As I walked around Lowes, a brand of hot water heaters incorporated refrigeration equipment to produce hot water. Obviously, this system of hot water generation is a heat pump. I did not check out the specs at the time but in due time I may do so. So, it is conceivable that you inquiry has merits.

 

[urgross]

A heat pump with desuperheater is often used for domestic hot water, or even radiant floor heating. Doesn't work so good in winter where I'm at, but during summer will improve heat pump efficiency. You should be able to get a quick estimate using ASHRAE Handbook HVAC Applications, Chapter 49.

 

[Noway2]

There is another factor to consider: your cooling load. If you have a need for both hot and cold water, a heat recovery chiller could give you an overall better efficiency and lower cost than a standard chiller and boiler combination.

 

[urgross]

Yet another factor is whether you will be requiring any dehumidification. A heat recovery chiller or de-superheater could possibly provide a reheat if your control scheme is to control humidity with the cooling coil.

 

[317069]

What if you need demotic hot water and at the same time the heat pump is in heating mode,

 

[urgross]

That's why it does not work so well as a standalone system at this location. Supplemental, either electric insta hots or steam are used as the supplemental for here. Can't speak for other locations without weather data.

 

[chicopee]

Electric heat as supplemental will have its draw back and that is when there is an extended power outage. We all remember the snow and ice storm, about two and half years ago when the entire Northeast had power outage, my gas fired hot water heater with its pizzoelectric ignition still generated hot water while a good portion of my city and states had no hot water for at least a week and in CT power was not restored for several weeks. It is worthy to remember that electricity has its drawback.

 

[fayeque]

HI Everybody,

Thanks to all for taking your time and writing.

Let me elaborate more on it.

the place where i am trying to suggest this solution has very low electricity cost as compared to Natural gas for gas fired boiler.

The existing scenario- there are Gas fired boilers generating hot water at 78 deg c which is routed through Calorifier(Plate and shell type heat exchanger)to Boiler for heat exchange. The calorifier supply and return temperature is 60 deg C(required at storage tank) and 55 deg Celcius.

What i am suggesting is - to generate direct 60 deg celcius hot water and suppliet to storage tank. and additional benefit will be chilled water generated which i can route to Chilled water tank and will reduce loading on existing chiller.

Hope i clarified..please feel free to ask any doubts or share suggestion with me.

Please let me know or else i will take time and prepare schematic of existing scenario and share with you guys.

Thanks in advance,
Regards,
Fayeque

 

[Noway2]

What i am suggesting is - to generate direct 60 deg celcius hot water and suppliet to storage tank. and additional benefit will be chilled water generated which i can route to Chilled water tank and will reduce loading on existing chiller.

Based upon this statement, I repeat my earlier suggestion of a heat recovery chiller. Unlike a normal chiller where the control point is the cold water temperature, these are controlled off of the condenser water temperature. 60C*9/5+32 = 140F, which is a standard temperature for this operation with the reject waste product being the cold water from the evaporator, which you have a use for. Pushing the condenser to 60C/140F will cause your KW/ton to be higher than a pure cold water chiller operation, but the overall cost for both hot and cold water, especially with inexpensive electricity is typically lower. I would recommend contacting a commercial HVAC representative who can recommend a system for you with a cost analysis instead of agonizing over the idea in an internet forum.

 

[fayeque]

Thanks Noway...I am in total agreement with you...

 

[317069]

Your application is an hotel, you have chiller system serving this application, you have gas fired boilers to generate domestic hot water, electricity is way cheaper than gas fuel, you want to use a heat pump instead of gas fired boiler, am I correct?
now, to get a heat from heat pump, the heat pump should be in cooling mode, what would cool this unit as long as you have already a chiller system for HVAC.
- heat pump is an HVAC tool, it is not designed for hot water production, the domestic hot water is water for human use, did you see someone drink or get a shower directly from hydronic heating or cooling system without heat exchanger,
- as long as electricity is way cheaper than gas, then way don't you use electrical water heaters, it is cheaper, easy for installation and more efficiency.

 

[Noway2]

See:

http://www.docs.hvacpartners.com/idc/groups/public/documents/marketing/04-581025-01.pdf

It discusses using a chiller for hot water production, with chilled water as a byproduct, giving several example applications.

 

[317069]

It says:
As a result, this water must be protected
from contamination from potentially harmful sources.
Many codes require the separation of the potable hot
water source from non-potable sources by means of a
double-wall vented air gap in the heat exchanger as a
minimum. This would minimize the risk of internal
leakage and cross-contamination between the two
fluids.
Fayeque has suggested to direct the water directly from heat pump condenser to water storage tank, that was my point.

 

[rickitek]

im from hotel industry. in my previous job we use heat pump to generate hot water at 55C and cold air at 25 to 28C which i supplied to nearby supplies stock room, it could produce as much as 60C hot water as per the supplier but i never attempted that as im already fine with 55C. its a 115rooms hotel. i already forgot the capacity of the unit and other technical specs but it works well and doesnt give me headaches. i think it is best suited for mid-size hotel and cost effective compared to electric heating. for 500rooms hotel and up i think boiler wins in terms of operational cost as you can also use steams for kitchen and laundry,

 

[willard3]

Where is electricity less expensive than gas per million btu?

 

[chicopee]

Good question willard3; Saudi Arabia, Qatar, United Arab Emirates perhaps.