Residential Heat Pump Water Heater

[XR250]

How are these things efficient if they are inside your house.? Ok, free A/C in the Summer. But in the winter, they are just transferring the load to the HVAC system. Maybe they make sense if they are in an un-heated garage?

 

[MintJulep]

In a warm space the heat pump needs to do less work, so by itself it's more efficient.


The ones here in Japan have the evaporator outside.

 

[XR250]

I get it if the Evap is outside. But if it is inside, like most, the cost of it doing less work in the warm space is born by the heating and air system.

 

[LittleInch]

Do you mean stand alone ac units?

An example would be good to understand.

And very little is free......

 

[XR250]

IDK if you are referring to me or MintJulep?

This what I am referring to...

 

[HVAC-Novice]

How are these things efficient if they are inside your house.? Ok, free A/C in the Summer. But in the winter, they are just transferring the load to the HVAC system. Maybe they make sense if they are in an un-heated garage?

Maybe detail what exact product and in what application, setup and climate you are talking about. You can make a technology efficient, or inefficient depending on how you use it.

 

[LittleInch]

IDK if you are referring to me or MintJulep?

This what I am referring to...
View attachment 3459

I did mean you and thanks for confirming what I thought you meant.

"How are these things efficient if they are inside your house.?" They aren't. If you place them in the middle of a home where the exhaust fan blows freezing cold air into your heated space.

I kind of get what you mean by free a/c in that if you heat your water by electric then yes, this is getting cold air for the same or less heat input.

Like any heat pump system, you need to be extracting your heat from the ambient air outside your house for it to make sense in the winter. of course to make use of the cold air in the summer you need it inside your house, but then it won't run as much as the water is warmer and you tend to use less hot water.

 

[XR250]

Exactly, That is why I don't get these things. I think if you look at the overall energy consumption of the house, there ain't much benefit and you have all the downsides of the mechanical complexity and upfront cost.

 

[HVAC-Novice]

Exactly, That is why I don't get these things. I think if you look at the overall energy consumption of the house, there ain't much benefit and you have all the downsides of the mechanical complexity and upfront cost.

If you are in a cooling climate where you air-condition most the year, those can make sense. The room they are in need to be coupled to the rest of the house (i.e. not in garage or a small sealed room).

They also could work in a non-freezing climate where you have the water heater in the garage or some other space connected to the outside.

Other than that, I don't see them being beneficial.

 

[XR250]

Agreed. Seems like they are oversold by contractors, marketers, power companies and the EPA.
Better to do solar hot water if possible. I had it at my last house and it was great.

 

[HVAC-Novice]

Agreed. Seems like they are oversold by contractors, marketers, power companies and the EPA.
Better to do solar hot water if possible. I had it at my last house and it was great.

Heatpump is the new fashion word. Like "hydrogen". It all sounds good until someone with knowledge in thermodynamics looks at the details....

Heatpumps CAN be great, but only in the right application.

 

[XR250]

Meh, HVAC heat pumps are way more versatile than heat pump water heaters as they will work effectively in most parts of this country - or world for that matter.

 

[HVAC-Novice]

Meh, HVAC heat pumps are way more versatile than heat pump water heaters as they will work effectively in most parts of this country - or world for that matter.

A heat pump is a heatpump. Thermodynamics are the same. Efficiency mainly depends on the lower and higher temperature (plus heat exchanger capacity, compressor/motor efficiency, type of refrigerant). Thermodynamics doesn't give a hoot if the person installing it is in a Plumbing or HVAC union.

If that water you heat to 130°F from a 0°F ambient is used for HVAC, or plumbing, is not relevant. A given heat pump under hose operating conditions will have the exact same COP.

 

[LittleInch]

The all in one unit heat pump water heaters are only really going to work in specific circumstances where the cold/ cooler air coming out of it isn't going to cause a problem.

Split units are far better.

 

[XR250]

The all in one unit heat pump water heaters are only really going to work in specific circumstances where the cold/ cooler air coming out of it isn't going to cause a problem.

Exactly my point. Most of the ones sold are all-in-one.