Questions tagged [hvac]
Questions about air heating, ventilation, and conditioning, including indoor air quality (IAQ).
82
questions
1
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2answers
38 views
Can a vacuum in a room increase the pressure in a tube?
Ok, So I work as a Marine Engineer but I do not have an engineering degree so I am having a hard time wrapping my head around this problem.
So currently on my ship we had a minor spill overboard from ...
1
vote
1answer
13 views
Nitrogen purging via outdoor unit: Gas not going thru?
I'm installing a new Daikin 4MXL (36K BTU) outdoor compressor, with 24K and 9K indoor unit (I previously installed a smaller dual zone Daikin)
One of new indoor unit's lineset will be behind drywall, ...
0
votes
0answers
11 views
Enclosure temperature regulation using recirculated exhaust
I need to put a Dell PowerEdge C2100 server in a detached garage in Colorado with no HVAC. I'm trying to figure out how to design an enclosure around the server that will recirculate hot exhaust air ...
1
vote
3answers
78 views
What is the maximum temperature that could be achieved by a heat-pump and will it affect its efficiency?
I did some research and found out that one of the applications of a heat pump is as a water heater which means that it could achieve a temperature of about 100-degree Celsius.
Will changing the ...
0
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0answers
17 views
What is the pressure of water-dew resulted from cooling of atmospheric air down to dew point temperature?
Suppose, In a room, Air is at 1 atm presssure. So should be the pressure of any water surface in the room. If the room temperature is cooled downed to dew point temperature, vapor (moisture) will ...
1
vote
3answers
61 views
Practicality of energy recovery from HVAC systems?
I've been thinking about ways to maximize efficiency in large buildings, and one thing I thought of was to place some sort of turbine in the exhuast vents or smokestacks of factories, power plants, ...
2
votes
2answers
75 views
Does venturi effect helps in reducing temperature of a room?
I clearly didn't understand how this works, but the explanation and claim that it reduce the temperature of room by 5°c made me wonder, here I am trying to understand the Venturi-effect on temperature
...
2
votes
1answer
114 views
Throttle vs Choke vs Damper vs Valve?
Throttles, chokes, dampers, and valves all restrict fluid flow. Aside from specific terminology/usage in internal combustion engines, are these really interchangeable terms, or do they have some ...
3
votes
1answer
56 views
Why do a swamp cooler and dehumidifier effectively cool a room when paired together in an enclosed space?
I've read in more than one place (e.g., here and here) that a swamp cooler (a.k.a., evaporative cooler) can be effectively paired with a dehumidifier to cool an enclosed space, but this makes no sense ...
0
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0answers
58 views
Axial fan for HVAC with HEPA filters
I have a background in mechanical engineering but HVAC is not my specialization. I am trying to properly size an axial fan to get a determined airflow from a duct. Both inlet and outlet are at ...
3
votes
0answers
25 views
Electrical component most likely to fail in window AC unit after power surge?
I have a window AC unit, 115 VAC, 10 amps. Power went out earlier in the week due to the big storm on the east coast and once it came back on every LED on the control panel was lit (not typical) and ...
2
votes
2answers
36 views
RV HVAC and Fridge Freezer on the same coolant loop?
Given the space, weight, and power constraints of an RV it is useful to make as much use as possible out of every component. Is there an engineering reason why a refrigerator / freezer and an air ...
4
votes
0answers
32 views
Do high speed trains use ventilation and filtration systems similar to aircraft?
This article discusses the ventilation and filtration in aircraft:
Ventilation rates provide a total change of air 20 to 30 times per
hour. Most modern aircraft have recirculation systems, which ...
0
votes
1answer
22 views
Climate control in data centers
I'm a student currently working on a market research project on the HVACR industry, and I'm having trouble nailing down a simple answer to these questions (it may be there are no simple answers, as so ...
1
vote
1answer
41 views
How can you maximize air flow through a sound maze in a HVAC transfer grille?
My house has several transfer grilles like this:
Except they have no baffles inside them, so light and sound come through into our bedrooms quite easily. I'd like to put in a sound maze like this to ...
0
votes
1answer
896 views
Can Peltier Modules be practically used to cool a room?
I am thinking of building a indirect Peltier AC to cool a room of approx size 30m3. Single/multiple peltier modules will be used to cool a insulated box with water inside. The box will be kept outside ...
1
vote
0answers
24 views
Raining indoors
I have heard stories about buildings such as hangars or large arenas where under the right conditions, clouds could form and it could rain within the building.
Is there a specific name for this ...
2
votes
3answers
46 views
HVAC Bag Filter Backwash
I need to install a replacement air handler in a facility that has an area where a large volume of particulates are in the air. Unfortunately, the previous designer tried to get away with the ...
2
votes
0answers
22 views
Energy/Efficiency Calculations for Large Multi-stage Package HVAC
I frequently use the Equivalent Full Load Hour (EFLH) estimation method to calculate the expected energy usage for commercial HVAC equipment. While not ideal, it works well enough to given an order ...
1
vote
1answer
37 views
energy unit conversions
This is an HVAC mechanical engineering question on a document from a manufacture where they convert units of electrical energy to therms of natural gas.
Carrier has writeups for building energy ...
0
votes
1answer
31 views
How does indoor temperature factor in when determining ideal relative humidity in a home?
I am having trouble understanding how indoor temperature plays into what a healthy indoor relative humidity level should be. Most sources I have come across searching the topic online provide a range ...
1
vote
0answers
11 views
How does plant evapotranspiration reduce the required size of a chiller used to control the climate of an indoor farm?
When HVAC companies estimate the required size of a chiller unit for a greenhouse or an indoor farm, they reduce the estimated load by plant "transpiration cooling." I understand how transpiration ...
1
vote
3answers
176 views
What's the current nomenclature for “English” system of units?
Is the term "English units" still in current everyday use? I do hear this term among other engineers I work with but I'm unsure if this is a localized usage or is consistent with the wider community.
...
0
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3answers
37 views
How to dump moist air without heat backflow in evaporative cooling system?
I'm looking to design or purchase an evaporative cooling system for a small 70ft^2 California dorm room without air conditioning. This room has a single window and door to a large common space with a ...
2
votes
0answers
26 views
Solar Heat Gain/Outside Temperature Effects on a House
I'm currently a sophomore Mechanical engineering student and need some help with an equation for my project. I am coding a simulation in Matlab and have been given a very short time frame to do it. I ...
0
votes
2answers
683 views
Air conditioner using liquid nitrogen and a cryogenic heat exchanger
I have been trying to understand if compressor-based systems in air conditioners can be replaced to make something more economical and energy efficient.
From what I understand, the compressors ...
0
votes
1answer
1k views
Estimating fan CFM from RPM, HP, and diameter
I am trying to determine the approximate CFM of several axial flow fans being used in agricultural storage in the developing world. The only information the storers have is the power, RPM, and ...
2
votes
2answers
39 views
Can I oversize my air conditioner if I use a two speed compressor?
The upper floor of my house has a split A/C, three-ton. When the temperature gets up above about 95 Fahrenheit, the unit can't ...
1
vote
3answers
150 views
How can I calculate the amount of heat my copper water trap can dissipate?
My small (1.5hp) air compressor is connected to a water trap made of 8mm copper of about 4 metres length. The idea is that you push the compressed air through the piping which cools it, condensing the ...
2
votes
1answer
85 views
What is the difference in CFM, at a given static pressure, between a CPU fan and a Squirrel Cage Blower fan when moving air through ductwork?
I have a Delta ASB0912L DC Brushless fan. PDF here.
In the datasheet it says,
RPM 3800
CFM 67.80
IN H2O 0.302
On the blower, squirrel cage fan, Dayton from ...
2
votes
1answer
86 views
Wet bulb temperature in psychrometry
"In a sling psychrometer(with dry and wet bulbs), if the moist air is not saturated(with water vapour) then it evaporates some water on the wet bulb and in turn cools the wet bulb.So the wet bulb ...
4
votes
4answers
2k views
How does an expansion tank work?
I know that a hydronic system forms a closed loop. When the boiler is turned on, the water temperature will increase and expand. Since this system forms a closed loop, there is no volume for the hot ...
1
vote
0answers
36 views
Air handling unit design
I am currently developing an AHU for all weather conditions.
I need the design process for calculating coil capacity and air discharge rate.
Issue is that, while plotting the process on psychrometric ...
0
votes
3answers
2k views
Effectiveness of positive pressure in highrise buildings?
The common knowledge these days seems to be that positive air pressure pumped into the common hallways of highrise buildings will allow smokers and non-smokers to live in the same highrise. Good ...
2
votes
0answers
81 views
Determining the load on a pump vibration isolator
It seems to me that pump vibration isolators need to support:
The weight of the pump
The weight of the water in the pump
The weight of the water (only) in the drop to the pump
The supplier of ...
4
votes
2answers
984 views
Why home Air Conditioning AC compressor insulated
Compressor is hot due to gas compression, and the gas then cooled in condenser. AC installed in tropical climate. Why compressor have insulation barrier?
1
vote
0answers
45 views
Does a TXV completely close when there's no thermal load whatsoever?
How is a TXV supposed to behave in a no evaporator thermal load situation (for example, evaporator fan completely off)? Would it completely close, not letting any liquid refrigerant get through (and ...
0
votes
1answer
67 views
Defining fresh air rates for sizing heating coils
dear StackExchange colleagues;
If I want to find the fresh air rate in kg/s and the supply rate in kg/s during winter and summer for the case below:
DATA:
Indoor condition all year = ...
3
votes
1answer
171 views
Why is it more common to use ceiling fans instead of air pumps?
As the title suggests, why not use high-powered air pumps instead of ceiling fans to inject hot air from the ceiling down to the cold, bottom floor?
I understand it may seem silly (especially since ...
0
votes
1answer
24 views
How to integrate air duct into roof insulation & bituminous sheeting?
This is the situation: We have a flat concrete roof with (from bottom to top) bituminous sheet, insulation, bituminous sheet. There's a blower to be set onto the roof, blower has a stand with a broad ...
0
votes
1answer
105 views
Do 36 inch diameter fans exist that push 25,000 CFM?
I own a warehouse that needs to push 25,000 CFM. I currently have an old warehouse exhaust fan that doesn't push anywhere close to this. The diameter of the fan blade is about 36 inches, but the ...
3
votes
2answers
57 views
A humidifier before a heater and after a heater
What is the difference between installing a humidifier before a heater and after a heater?
3
votes
2answers
2k views
How to cool down a warehouse?
I have a warehouse ( 36m x 14.4m x 10m ) that I want to keep it under 30 degrees Celsius but everyday the temperature will goes above that. It has two turbine ventilator that I don't know the ...
3
votes
4answers
174 views
Rapidly cool a flue gas without water circulation
I am a newbie at this!!
For an experiment, I have a diesel generator that releases hot flue gases at 150-160 Degree Celcius.
I want the output gas to be at less than 75 degrees for a duration of ~ ...
-1
votes
1answer
54 views
what is the air speed of an HVAC central air system return at the filter?
I figured I would ask here before going out and buying an anemometer. for a 20" by 25" HVAC Return (or just state the size W x H that your data is based off). Assume a 3 ton system. what is the ball ...
1
vote
0answers
17 views
External Static Pressure on Open Gallery Fan
I routinely work on building designs that incorporate rooftop upblast fans over large industrial spaces such as this one:
When selecting these fans, as with every other fan, you need to determine the ...
1
vote
2answers
108 views
Temperature dependent electricity consumption of HVAC System
I am trying to figure out if there is a decrease in electricity consumption of a cooling unit if the ambient temperature decreases from 35°C to 20°C. More detailed, a company is planning to install an ...
9
votes
4answers
3k views
Humidity in home is much higher than outside
We have a two year-old, two-story town house with:
fiberglass insulation in the walls;
a Tyvek vapor barrier under foam board on the exterior walls;
blown cellulose insulation in the attic;
stucco ...
1
vote
0answers
17 views
What would be the disadvantage if any to placing evaporator casement beneath furnace for central forced air HVAC sustem?
I have only been in the HVAC business for 3 years and I have already encountered 2 cases of leaking air conditioning evaporators. In both cases the evaporators were located above the central furnace ...
-1
votes
2answers
87 views
Good or bad (AC Split compressor input with cold freon)
Hermetic Compressor is used by split Air Conditioning unit. The compressor compressed freon gas coming from indoor unit. The gas is usually quite cold (about 2 deg.C lower than inside room temperature)...
