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 ...
- 5,282
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 ...
- 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 ...
- 10.4k
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 ...
- 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 ...
- 24.3k
7
votes
Accepted
Dead Load / Self Weight for ceilings & HVAC
I don't think what you are looking for really exists, in terms of a standardized list of HVAC/services loadings. Building codes don't usually specify dead loads, probably because they are, in ...
- 2,631
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 ...
- 3,751
6
votes
Why do boiler exhaust stacks use tapered transitions?
The taper in the stack performs two functions:
A tapered section is a lot more structurally resistant to wind loads
This seems counter intuitive at first - after all, a tapered cantilever beam ...
- 5,343
6
votes
Accepted
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 ...
- 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 ...
- 7,904
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,...
- 789
5
votes
Effective R-value of radiant barriers
Insulating against thermal conduction can be represented as an R-value because it is a linear calculation. I can add two or more R-values together and I will see a linear benefit.
Insulating against ...
- 7,904
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 ...
- 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 ...
- 7,904
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 ...
- 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 ...
- 15.5k
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 ...
- 4,772
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, ...
- 24.3k
4
votes
Accepted
Identify this textbook
Thermal Environmental Engineering 3rd Edition by Kuehn, Ramsey & Threlkeld (1998), Pearson.
- 2,467
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 ...
- 4,607
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 ...
- 149
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 ...
- 1,174
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. ...
- 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 ...
- 1,000
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 ...
- 14.3k
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.
- 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 ...
- 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, ...
- 2,467
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 ...
- 14.3k
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 ...
- 15.5k
Only top scored, non community-wiki answers of a minimum length are eligible