HP Performance Experiences

pecmsg

unclejohn said:

When the suction pressure drops you are using less power but you're capacity drops with it. You no longer have say 24k btu output from your 2ton HP. Less cap less power less heat. There is no magic 

This is why in refrigeration we use Horsepower not tons. A 1-Ton A/C compressor is 3/4-HP or 1/2-HP depending on the evaporator temperature.

Jamie Hall

sigh... there's a reason I stopped trying to teach thermodynamics

ChrisJ

Jamie Hall said:

sigh... there's a reason I stopped trying to teach thermodynamics

It's interesting you now have three people with real world experience, who understand what's going on telling you exactly what happens and you still don't believe it.

I'm not sure why.


According to your theory, a gasoline engine should run full output even with the butterfly valve mostly closed because apparently it's still going to pull in a full charge per stroke.

unclejohn

I thought I was agreeing with Jamie.

Jamie Hall

OK, let's look at that gasoline engine, and we'll assume for the moment that it is a carbutetted engine. There are actually two butterfly valves in a carburetor, so we'll assume for the moment that we are speaking about the throttle valve, which is located between the carburetor throat and the intake manifold (the choke valve is located between the air intake and the carburetor throat, in carburetors so equipped, and has a very different effect).

Now let us suppose the valve is fully open. There is no restriction to flow between the throat and the manifold, except normal piping losses. The mass of air flowing will be determined by those losses (and, in some cases, by the velocity of the air in the venturi throad -- but that's another matter). Now let us suppose that the throttle valve is closed. This imposes much greater friction losses, so the mass air flow -- which is determined by the balance between the available pressure difference between the manifold pressure and the free air intake pressure (no blower on this engine) -- will be much less.

Note that the volume of air pulled into the cylinders will be much the same. However, it will be at much lower pressure (because of the pressure loss past the closed throttle) and, therefore, density, so the mass of air -- which is what matters -- will be much less. This can be seen in more recent fuel injected gasoline engines, where the throttle valve again controls the airflow in the same way, but the sensor which determines the fuel flow is called the "mass airflow sensor" because that is exactly what it is.

In either case, the power of the engine is controlled entirely by the mass (repeat after me: MASS) of the air ingested, assuming that the proper ratio of gasoline is present in that air.

Superchargers (whether mechanical or turbo driven) work by compressing the air -- more density, more mass per cubic inch, more power. Engines lose power at higher altitudes -- less density, less mass per cubic inch, less power (at the risk of confusion -- a blower, such as is found on two stroke engines, particularly diesels, has a completely different purpose).

In all cases the volume of air passing though the cylinders is very nearly the same -- in a four stroke engine, half the displacement per revolution -- but the pressure, and hence the density and therefore the mass differs.

The energy involved in most -- I can't think of an exception -- chemical reactions or phase changes is determined by the mass of the reactants, not the volume if they are gasses. Perhaps part of the problem is that most people never think about the mass of a gas -- just as they never think about the pressure of the atmosphere (try explaining the difference between absolute pressure and gauge pressure and watch the eyes roll up) and yet it is mass we need to think about (and absolute pressure).

I'll keep trying. I don't expect to get anywhere...

ChrisJ

unclejohn said:

I thought I was agreeing with Jamie.

Perhaps I'm just misunderstanding what Jamie is saying.
I said as the evaporator pressure drops power consumption drops and the compressor works easier, not harder and of course the system output decreases.

It's my interpretation, Jamie is saying the opposite happens, power consumption increases and output remains the same.

WMno57

You guys are making my brain hurt. But that's good. I don't understand most of what Jamie is writing about. That's good too. After I read it multiple times and google a few things, maybe I'll learn something.
I do enjoy Wall threads where experts disagree. I learn more from trying to follow those threads.

Jamie Hall

Perhaps the problem here, @ChrisJ , is that when the evaporator pressure drops if the compresor displacement per unit time stays the same, the mass flow through the compressor will also drop (lower density of the gas at the intake). When this is the case, the flow restriction to the gas on the condensor side must increase to maintain the condensor pressure so as to maintain the condensing temperature. Then there will be drop in system output. Compressor power requirements will also drop, as the mass of gas being compressed is significantly less.

I was sort of assuming that we were trying to maintain a constant power output from the condensor.

ChrisJ

Jamie Hall said:

Perhaps the problem here, @ChrisJ , is that when the evaporator pressure drops if the compresor displacement per unit time stays the same, the mass flow through the compressor will also drop (lower density of the gas at the intake). When this is the case, the flow restriction to the gas on the condensor side must increase to maintain the condensor pressure so as to maintain the condensing temperature. Then there will be drop in system output. Compressor power requirements will also drop, as the mass of gas being compressed is significantly less.

I was sort of assuming that we were trying to maintain a constant power output from the condensor.

I believe heat pumps use a TXV or EXV outside at the evaporator, so they're still "throttling" the evaporator in that situation and the condenser just ends up whatever it is.

The evaporator is what needs to stay fairly full, but not flood back to the compressor so its still the point of interest.

WMno57

I get that BTU output of a heat pump decreases as outdoor temperature decreases. Doesn't COP also decrease as outdoor temperature decreases? If so, wouldn't that imply that electricity consumed per BTU of output increases?
Maybe COP decreases less with inverters, vapor injection, refrigerants other than 410, and multiple stages, but COP still drops as outdoor temps drop. At some low outdoor temp you are putting hours on an expensive Rube Goldberg machine for what? A 10 or 20 percent improvement over electric resistance heating?
I don't trust the DOE or Heat Pump manufacturers to have software on heat pumps that make the decision to cut over to electric resistance heat strips when it would be in the user's best TCO (Total Cost of Ownership) interest.

ChrisJ

WMno57 said:

I get that BTU output of a heat pump decreases as outdoor temperature decreases. Doesn't COP also decrease as outdoor temperature decreases? If so, wouldn't that imply that electricity consumed per BTU of output increases?
Maybe COP decreases less with inverters, vapor injection, refrigerants other than 410, and multiple stages, but COP still drops as outdoor temps drop. At some low outdoor temp you are putting hours on an expensive Rube Goldberg machine for what? A 10 or 20 percent improvement over electric resistance heating?
I don't trust the DOE or Heat Pump manufacturers to have software on heat pumps that make the decision to cut over to electric resistance heat strips when it would be in the user's best TCO (Total Cost of Ownership) interest.

I'm pretty certain the efficiency drops and overall power consumption (run time) probably climbs quite a bit.
But, the actual power consumption of the equipment in real time, I feel goes down.

Meaning, instead of drawing 18A it drops to 15A, but it runs much longer.

Jamie Hall

You are both correct. The COP does drop -- significantly -- and the output also drops. End result -- for a given BTUh average output, total electricity consumption goes up, even as running consumption goes down. There's no free lunch...

Total aside. Did you know that the cfm rating for a carburetor is based on the total area of the throats of the venturis and on the ratio of the total throat area of the venturis to their total intake area? And the basis is that you can't exceed Mach 1 at the throat? Trivia for the week...

ChrisJ

Jamie Hall said:

You are both correct. The COP does drop -- significantly -- and the output also drops. End result -- for a given BTUh average output, total electricity consumption goes up, even as running consumption goes down. There's no free lunch...

Total aside. Did you know that the cfm rating for a carburetor is based on the total area of the throats of the venturis and on the ratio of the total throat area of the venturis to their total intake area? And the basis is that you can't exceed Mach 1 at the throat? Trivia for the week...

Why can't you exceed Mach 1?

Jamie Hall

too much pressure drop through the shock

JDHW

I predict this thread will go to 4 pages!

John

ChrisJ

Jamie Hall said:

too much pressure drop through the shock

JDHW said:

I predict this thread will go to 4 pages!

John

Jamie,
We need to start a new thread on venturis.

JakeCK

It is interesting how threads evolve. This started as a post asking about personal experiences with heat pumps in extreme cold. It evolved into a debate about how much power a compressor uses at different ambient temperatures. 

ChrisJ

JakeCK said:

It is interesting how threads evolve. This started as a post asking about personal experiences with heat pumps in extreme cold. It evolved into a debate about how much power a compressor uses at different ambient temperatures. 

Come on Jake, you know no one's actually using heat pumps in extreme cold.

Contact a few people in Fairbanks or even International Falls, no one will be using heat pumps at -40 to -70F.

I do not consider 0F to be extreme cold. It's cold, but not extreme. When propane stops boiling at atmospheric pressure, you're in the extreme territory.

hot_rod

I think you are going to need to keep searching various discussion boards and chatrooms to find actual experiences.

Some manufacturers have case studies, some research has been done by Universities. Sounds like you want info from actual users, datalogged experience.

Your question is still vague, are you looking specifically for A2A, HPWH, A2WHP, Mini Splits, Earth loop system?


https://www.energy.wsu.edu/documents/Sanden_CO2_split_HWPH_lab_report_Final_Sept 2013.pdf

NrCAN has some info for Canadian markets.

JakeCK

For my use case a2w but that is going to be much rarer and is a newer technology altogether, but just personal experiences in general from any air source heat pump in what would be considered extreme cold for the contiguous US. Lol

JakeCK

ChrisJ said:

It is interesting how threads evolve. This started as a post asking about personal experiences with heat pumps in extreme cold. It evolved into a debate about how much power a compressor uses at different ambient temperatures. 

Come on Jake, you know no one's actually using heat pumps in extreme cold. Contact a few people in Fairbanks or even International Falls, no one will be using heat pumps at -40 to -70F. I do not consider 0F to be extreme cold. It's cold, but not extreme. When propane stops boiling at atmospheric pressure, you're in the extreme territory.

My father spent a good amount of time in Fairbanks. He had a friend who built a cabin along the Yukon. And then a second cabin when the first was destroyed by the ice breaking up. If I'm remembering the story correctly. Used to have photos of him up there too including one with him on horseback with the Yukon behind him. They were all lost when my aunt's basement flooded.

hot_rod

I took the SpacePak installers online class last year. They went over a few installations of the early version Solstice A2Whp, going back maybe 8 years or more in the upper NE.

I suspect a lot of shoppers would like to talk to those homeowners for first hand info.

My impression is that the manufacturers data is fairly accurate, as @Jamie Hall mentioned, it’s thermodynamics. It can be calculated, simulated, lab tested.

More importantly, for most is longevity, knowledgable service contractors, parts availability. And the cost and availability of electricity as years go by. Those answers are not so black and white.

Reminds me of the late 1980’s when a plastic box called Munchkin was the rage.

Someone needs to be the volunteer to try the current equipment rage. Might as well be an inquisitive fellow like you. Report back🤩

JakeCK

I really do want to try an a2w hp, but I have yet to find a reputable installer. And trying to purchase the equipment directly so I can install it my self has been difficult. I have only found one manufacturer that sells direct and I have my reservations with them. They're kind of light on the details.

JDHW

Bit of data from a few sites in the uk.

https://heatpumpmonitor.org/

John

Matt_67

We have a handful of air to air heat pump installations (Mitsubishi Hyper-heat, Trane XV20i) in a -7 design area. All of them have alternate or supplemental heat sources available. In the design phase we plot the heat loss of the building against the capacity of the heat pump, so the customer knows what they are getting. The performance is generally a touch better than expected, which makes sense considering that heat loss calculations tend to be conservative. But the lower COPs at colder temperatures encourage most people to throw some wood in the stove.