# Tag Info

27

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 temperature are mainly sensitive to heat transfer and changes in temperature, not so much absolute temperature values. For example, here's an interesting excerpt from ...

15

Your question sort of has two parts: How to supply heat, and how to keep it in. Large open rooms with a high ceilings are most efficiently warmed with radiant ceiling heat. Warm air rises, which renders forced-air systems inefficient because the pumped heat ends up at the ceiling and the coldest part of the room is near the floor where you actually want ...

8

Another option to the radiant solution above would be under floor air distribution systems (UFAD) using displacement ventilation. These systems require a raised floor plenum which works well in theatre style auditoriums, where you often have this anyway. The plenum essentially becomes your supply duct. The systems are sized to condition the occupied zone ...

8

You need to consider the density of the air, which varies with temperature and air pressure. At 15 degrees Celsius, at sea level, the density of air is 1.225 ${kg}/{m^3}$. The table here gives air densities at 5 degree intervals. Now density is mass divided by volume, ${\rho} = m/v$ Hence, to get the volume flow rate (in ${m}^3/s$), for a know mass flow ...

7

Lighters usually use Butane. Gas bottles use some or all Propane. Propane pressures are MUCH higher. A plastic 'tank' filled with Propane would probably explode. As size increases the container strength must be increased disproportionately. As temperatures increase pressures rise FAR faster than changes in absolute temperature. We understand from ...

7

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 principal, known. Typically only imposed (live) loads are specified. From the buildings I have worked on the services loadings were essentially copied from similar ...

7

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 cold air sinks. Normally, there's quite a bit of movement in the first two metres or so from the ground - thermal stratification starts when the ceiling gets to ...

6

Those two holes by themselves will have little effect. The pressure difference between the two ends of the holes will be so small that only a little air will flow. If you want to go thru all this trouble, then put a hole at the bottom too, with a fan that actively blows cold air from the bottom of the living room into the bedroom. Hot air will then find ...

6

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 with a fixed load at the end deflects more than a straight beam. However, there is less surface area at the top of the stack for winds to push. Since, in the US, ...

6

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 can only do this by straining the container, this creates very large stresses which are the cause of the pressure increase. To put another way the pressure ...

5

What you want is called a heat exchanger. Imagine two long air tubes with a thin wall between them. The air exiting the house travels in one tube, and entering air in the other, but in opposite directions. Over the length of the tubes, heat transfers thru the thin wall. Ideally, by the time the house air gets to the far end where the outside air comes in,...

5

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, resulting in very little actual exchange of air. What you really need is old technology. Double hung windows are what our ancestors used. The bottom sash ...

5

HVAC-Systems usually give a Volume-Flow-Rate, hence $m^3/s$. If you need Mass-Flow-Rate ($kg/s$) you simply need to multiply with the density ($\rho$) of the fluid. The density can be calculated using the ideal gas law (see 1): $$\rho_s = \frac{p_s}{R T_s}$$ Please observe that you need static values for the pressure ($p_s$, see 2) and temperature ($T_s$, ...

5

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 smaller temperature difference the rate of heat loss decreases. Moving air over the skin disrupts this boundary later allowing unheated air to be in contact with the ...

5

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 engineering perspective. Any of these trends would be helpful in debuggig the situation: Relative humidity and temperature at a discharge of the HVAC system ...

4

It depends — can you run air through the plenum without simultaneously running the active heating/cooling system? If not, you'll never get the benefit of its thermal storage capacity. For example, when heating, the plenum will always be hotter than the slab, putting heat into it. In order to extract heat from the slab, you need to be able to put ...

4

Here are some ways to keep the warm air from escaping: Revolving doors prevent a constant stream of air exchange between the inside and outside. Air lock areas - a double-set of sliding doors can also prevent continuous air-exchange. Positive pressure by the entrance, usually supplied by a fan heater above the inner entrance door ensures the main bulk of ...

4

I think you are getting power and energy confused, so I'll quickly define them before giving an answer. Energy energy is a measure of how much potential for work exists. If you had a battery, it contains a certain amount of energy. Once that energy is used, the battery is "dead" and must be recharged (or thrown away). This is usually measured in Joules (J) ...

4

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 thermal radiation is more complex: You can't add two radiation barriers and get one that is twice as good. Insulation is based on the temperature of the barrier ...

4

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 will give you a final relative humidity below 100% after the heater. This can be important if you want to avoid dew. Mounting the heater before the humidifier ...

4

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 transfer coefficient for air flow can be approximated to (see engineering toolbox link) $$h_c = 10.45 - v + 10 v^{1/2}$$ where $h_c$ = heat transfer coefficient (\$...

4

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, if you use a turbine to "suck" energy out the air then it tends to slow down. So then you would probably need to use bigger fans to push the air. So ...

3

Not to jump the gun from @hazzey, but one of the product description images describes how the cabinet works: The English in the images is a little lacking (probably a translation from a Chinese manual or something), but it seems like the cabinet condenses the moisture inside, then freezes it on a collection board. Once the space is dehumidified, it appears ...

3

Making a duct that flares along an exponential curve to 2 feet (60cm) in diameter would create a larger duct that won't solve your problem. It would be an expensive duct to make (think tuba bell), and if you focus on the flare instead of the overall dimensions, then the duct might come down too low and you won't have enough space. Keep in mind that a ...

3

The indoor temperature in the unheated case will be just the low pass filtered outdoor temperature. In steady state, therefore, the indoor temperature will be the same as the outdoor - at first glance. However, sunlight heating one or two sides or coming in through a window can make a big difference. Basically, there are too many variables to give a ...

3

For simple ventilation, opening a single window may not mean a lot of circulation. Air has to come in and out of the same window, so it just leads to eddies and turbulence next to the window, with conduction doing most of the work. Opening two windows allows a pathway for the air to flow in and out, and allows the air to mix in, which creates an open heat ...

3

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 tub of water, and divide the output exhaust into 4/5 tubes, take them through a tank of water?" A: Yes you can, but the heat exchange between the water and ...

3

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. Ventilation will only cool the warehouse when the outside temperature is less than the inside temperature. One way ventilation can help, if it's managed ...

3

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 account to determine where most humans would feel comfortable. This will tell you the range of optimum humidity percentages to shoot for at a given temperature ...

3

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.

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