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35 votes

How do heat pumps output more heat kW than the electrical kW used to run the heat pump?

In the traditional efficiency equation the power input is the power to run the compressor motor and the power output is how much mechanical power that motor is producing. In that case efficiency is ...
DKNguyen's user avatar
  • 5,526
27 votes

Why does moving air feel cold?

There are a couple reasons. First of all, it's important to note that the sensation of warmth or coolness is only indirectly related to temperature. The receptors in your skin that deal with ...
Air's user avatar
  • 3,211
17 votes
Accepted

Why isn't heatpump technology used for solar collector panels and boiler tanks?

Heat pumps work well to extract heat from one zone and discharge it into a zone at a higher temperature. The output of solar water-heating panels is generally much higher than the boiler tank ...
Transistor's user avatar
  • 10.6k
14 votes

How do heat pumps output more heat kW than the electrical kW used to run the heat pump?

A heat pump takes heat energy from one side, compresses it a bit (to get to a usable temperature) and transports it to another side. So you are more or less “stealing” energy from the outside of the ...
Michael's user avatar
  • 318
11 votes

How do heat pumps output more heat kW than the electrical kW used to run the heat pump?

Heat pumps (commonly) use vapor compression cycles (the following is a short summary of a longer article in tlk-energy.de). To understand this process, you only need the following three key physical ...
NMech's user avatar
  • 24.3k
7 votes
Accepted

Why is it more common to use ceiling fans instead of air pumps?

Mainly cost difference. And also, a fan is sufficient for the job. The problem being solved is thermal stratification. That's caused by a lack of vertical mixing; the warm air rises to the top, the ...
410 gone's user avatar
  • 3,751
6 votes
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How does an expansion tank work?

It is better to think of it in terms of volume than pressure. The key point is that air is compressible while water is not. If you heat water is has to expand. If it is in a closed container then it ...
Chris Johns's user avatar
  • 15.2k
6 votes
Accepted

Can Peltier Modules be practically used to cool a room?

Peltier thermoelectric cooling modules can be used to cool anything you like. It will not be economical compared to a standard off the shelf air-conditioner (R-134A compressor cycle). If you source ...
ericnutsch's user avatar
  • 8,136
5 votes

How does one create a draft in a room (with a single window)?

The fundamental problem is that hot air must leave the room and cold air must enter it, both at the same time through the same single opening. The conflicting forces will mostly cancel each other out,...
Ray Butterworth's user avatar
5 votes

Why does moving air feel cold?

The air feeling cold is really your skin being cooled by forced convection and evaporation of sweat. With no air movement a boundary layer of hotter air forms over the skin and so because of the ...
Farcher's user avatar
  • 151
5 votes
Accepted

Humidity in home is much higher than outside

Sounds like you have covered your bases. The only thing I can recommend is gathering data and considering some scenerios to evaluate that data against. I am not an HVAC guy but can give you the 1000ft ...
ericnutsch's user avatar
  • 8,136
5 votes

Does venturi effect helps in reducing temperature of a room?

I don't think it will drop the temperature at all. What it might accomplish is increase the velocity of the air in the room. That will in turn affect the convective coefficient The convective heat ...
NMech's user avatar
  • 24.3k
5 votes

Why isn't heatpump technology used for solar collector panels and boiler tanks?

The transmission of heat by phase change (liquid to gas and gas to liquid) IS used in some solar collectors. These are the evacuated tube type and are the "Rolls Royce" equivalent when ...
Solar Mike's user avatar
  • 15.6k
4 votes

A humidifier before a heater and after a heater

warm air can hold more moisture than cold air so the amount of water you can suspend in the air will change depending on where you install the humidifier. Mounting the humidifier before the heater ...
mart's user avatar
  • 4,781
4 votes

Practicality of energy recovery from HVAC systems?

So, if I understand correctly you are proposing to use a turbine in the exhaust vents in order to reclaim the energy from the flowing air. However, in most cases the air is flowing due to forced flow, ...
NMech's user avatar
  • 24.3k
4 votes
Accepted

Identify this textbook

Thermal Environmental Engineering 3rd Edition by Kuehn, Ramsey & Threlkeld (1998), Pearson.
StainlessSteelRat's user avatar
4 votes

Why isn't heatpump technology used for solar collector panels and boiler tanks?

You can't tie these two systems together because the demands on them are pretty much independent of one another. They each need to operate according to their own run schedule. The HVAC system runs ...
Phil Sweet's user avatar
  • 4,707
4 votes

How do heat pumps output more heat kW than the electrical kW used to run the heat pump?

A very simple answer. The heat pump has two different parts: inside and outside. The outside part of the heat pump takes outside air and cools it a few degrees. The heat removed from outside air is ...
ghellquist's user avatar
3 votes

How to cool down a warehouse?

keep it under 30 degrees Celcius but everyday the temperature will goes above that No amount of ventilation when it's hot out is going to fix that. In fact, more ventilation will make that worse. ...
Olin Lathrop's user avatar
  • 11.4k
3 votes
Accepted

Is a 3 Hz beat frequency from my neighbor's HVAC a sign of a malfunction?

A 3Hz pulsating hum-- noise that is getting louder and softer at 3Hz. Yes, I agree that would be quite annoying. Since this is a residential unit in the US, both the compressor and the fan are run ...
user1683793's user avatar
  • 1,000
3 votes

Rapidly cool a flue gas without water circulation

Your approach is not an unusual one, engine brakes to measure horsepower usually make use of such a method, but they use much bigger water barrels. To answer your questions: "Can I just fill a ...
Bart's user avatar
  • 1,184
3 votes
Accepted

How does indoor temperature factor in when determining ideal relative humidity in a home?

In the world of heating/ventilating/air conditioning engineering (a.k.a. "HVAC") there is a number called the comfort index (which you can search on) which takes both humidity and temperature into ...
niels nielsen's user avatar
3 votes
Accepted

energy unit conversions

I think the problem is just that you're expecting the solution to be more elegant; it looks like you already have it pretty much figured out.
Secundus's user avatar
  • 561
3 votes
Accepted

Throttle vs Choke vs Damper vs Valve?

Choke is usually just applied to starting fuel/air mix regulation for ICE engines, as far as I'm aware. Throttle is used to actively manage fluid flow while a device is operating. Dampers typically ...
jko's user avatar
  • 2,347
3 votes

Practicality of energy recovery from HVAC systems?

Energy recovery works best when it is a key component of the design. Solar Mikes example. From planning, design, operation and maintenance. Lose one of the four and it will fail. But as an addon, ...
StainlessSteelRat's user avatar
3 votes

Cooling system to maintain 0.5 °C at 95% humidity

At near-freezing temperatures, the amount of water vapor in the air to get 95% relative humidity is tiny, this is no problem. I recommend filling 55 gallon poly drums on pallets with water, park them ...
niels nielsen's user avatar
3 votes
Accepted

Can an AC compressor used as a Hydraulic pump?

No, the clearances, compression ratio and valves are not designed for that use. If you want a hydraulic pump then use a power steering pump, now available in two flavours mechanical ie engine or belt ...
Solar Mike's user avatar
  • 15.6k
3 votes

How do heat pumps output more heat kW than the electrical kW used to run the heat pump?

Simply the electricity input drives the compressor which moves the fluid around the system. The fluid is in one of two states: liquid or gas. The energy needed to convert liquid to gas and gas to ...
Solar Mike's user avatar
  • 15.6k
3 votes

How do heat pumps output more heat kW than the electrical kW used to run the heat pump?

For the same reason that a water pump puts out more water than kW used to run the pump. This analogy is easy to understand because what is being pumped is different than what is powering the pump. In ...
mark's user avatar
  • 31
3 votes

Why don't AC units run condensate over the outdoor condenser coils?

Designing a product for installation at site means that the designer has no idea or control over where the condenser coils are going to be. Will they be located over a door step? Over a car park? ...
Patrick McAuliffe's user avatar

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