Questions tagged [hvac]

Questions about air heating, ventilation, and conditioning, including indoor air quality (IAQ).

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17 votes
3 answers
7k views

What is the most efficient means of warming a building with a high ceiling?

Consider a large auditorium, a church, or some other very large, essentially one roomed building with a high ceiling. Suppose that the building has many entrances which enable cold air in/hot air out ...
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13 votes
3 answers
9k views

Why does moving air feel cold?

I'm taking a thermodynamics class and had the following question. I was going to ask my professor directly, but it seems like a stupid question with a simple answer, so I thought I'd try my luck here ...
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9 votes
4 answers
7k 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 ...
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9 votes
4 answers
2k views

Can air conditioners/dehumidifiers exhaust their waste heat in their exhaust water?

If I understand correctly, both air conditioners and dehumidifiers conventionally exhaust waste heat through their exhaust air, though both also produce exhaust water. I'd like to know, Are air ...
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  • 191
8 votes
1 answer
641 views

Air Conditioning Modes of Failure

I have a question about air conditioning and the probable modes of failure. I recently installed a Nest thermostat in my home. I've noticed that it seems to prefer to have the air conditioner's ...
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  • 213
7 votes
1 answer
1k views

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

I'm being annoyed by a pulsating hum which comes from my neighbor's HVAC system. I read up a little on the design of HVAC systems and I came to a tentative conclusion that what I'm hearing is a ...
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7 votes
2 answers
1k views

How does a compressor know to lower condensing pressure in chiller?

I am working on an indirect ammonia chiller that is used to cool the ice in an arena. The system consists of 3 reciprocating compressors, an evaporative condenser with a vfd on the fan, a float ...
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  • 307
6 votes
1 answer
686 views

Why do boiler exhaust stacks use tapered transitions?

We have a boiler exhaust stack with a base dimension of 120" ID and an overall height of 84'. 21' up, the stack begins a slow transition to 7'6" ID. The transition takes approximately 35' to reach ...
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6 votes
2 answers
11k views

Dead Load / Self Weight for ceilings & HVAC

I need to design the roof structure for a sports facility. I have no information with regard to HVAC design at this stage. Also, the HVAC may change in future. Thus I don't know what load to apply to ...
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  • 1,216
6 votes
1 answer
113 views

Where to insulate Underfloor air distribution system in a temperate climate

I have a proposed underfloor air distribution system (UFAD) for a one level office in a temperate climate. Typically the demand for heating and cooling in this climate is about even for offices. ...
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  • 377
6 votes
4 answers
3k views

How do dry storage cabinets work?

In my lab we use a number of materials which are hygroscopic and must therefore be stored in a dry environment. For that purpose we have numerous dry cabinets very similar to the one shown below (...
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6 votes
2 answers
2k 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?
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  • 238
5 votes
1 answer
179 views

How to minimize heat loss in an air extractor?

In an air-conditioned house equipped with an air extractor that removes for instance wet, smelly, etc. air from the bathrooms and kitchen, what are sensible cost-effective systems to prevent: Heat ...
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  • 153
5 votes
2 answers
116 views

What's more energy efficient: fewer air conditioners working at max capacity or more working at part capacity?

The central heat and air in the house I'm renting is unable to keep the house below 80 °F during the hot summer here (100 °F days). We've had 3 HVAC techs out to look at it and they all say there's "...
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  • 263
4 votes
4 answers
3k 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 ...
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4 votes
2 answers
74 views

Cooling system to maintain 0.5 °C at 95% humidity

I am looking for some guidance on a redneck cooling system. I need to store seeding trees at a temperature just above freezing, and at a humidity of close to saturation. I only need the system for ...
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4 votes
1 answer
1k views

Perfectly aerodynamic kitchen range hood

Short form: How would one calculate the perfect shape of a range hood? See drawing below. Will the curve of the profile of the range hood be exponential? Quadratic? What if the range is enclosed from ...
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  • 151
4 votes
2 answers
221 views

Inert gas use during HVAC line installation

When brazing HVAC linesets, the correct method is to flow an inert gas through the line in order to prevent interior oxidation of the copper and brazing products. However, as a specifier, I can say ...
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  • 561
4 votes
1 answer
2k views

Where to place fans for maximum effectiveness in sharing air conditioning between rooms?

I have a split-type inverter air conditioning unit in one room placed near the ceiling. Assume that the cooling capacity is met, and I'm using the correct CFM of fans. I would like to share this air ...
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4 votes
0 answers
130 views

Is it feasible to build a pedal-powered air conditioning booth?

Imagine it's hot and humid outside. You see a pedal-powered air conditioning booth. You get in the booth, close the door, and start pedaling. The pedals are connected to a shaft-driven (automotive-...
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4 votes
0 answers
49 views

Why is there limited use of Y (Wye) fittings in a refrigeration system?

I'm a Mechanical Engineering intern currently working in HVAC and Refrigeration for grocery stores. I'm looking into ways, with lower energy losses, to encourage equal flow distribution at liquid pipe ...
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3 votes
4 answers
249 views

Convective fix for air conditioning dilemma?

I live in a part of Mexico that can get really hot in the summer. I've got an un-airconditioned bedroom on the other side of a wall from a room cooled by a powerful Mirage mini-split AC. The problem ...
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3 votes
3 answers
14k views

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

There is a room on the south side of the building, which doesn't have any ventilation vents, but does have a window. Opening a window doesn't cause good air circulation (by which I mean that the air ...
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  • 445
3 votes
1 answer
182 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 ...
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3 votes
4 answers
248 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 ~ ...
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3 votes
2 answers
341 views

Effective R-value of radiant barriers

I know that radiant barriers (i.e., reflective films applied over or under insulated spaces) don't technically have R-values (because they primarily reflect heat, instead of primarily slowing ...
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  • 1,785
3 votes
2 answers
10k 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 ...
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3 votes
2 answers
64 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?
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3 votes
2 answers
192 views

Calculating kWh for different timestep

I have a simulation software which shows energy consumption at 30 minutes timestep. If a system consumes 0.06 kWh at 6am, and 0.09 kWh at 630am, how to calculate the energy consumption between 6-7am? ...
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  • 161
3 votes
2 answers
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 ...
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3 votes
2 answers
68 views

At what (outside) temperatures is it efficient to run my windowbox heat pump?

I am an electrical engineer that took two semesters of Thermodynamics about 4 decades ago. I am aware of the theory behind the Carnot cycle and such. I live in a condo in the Boston area that is all-...
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3 votes
2 answers
2k 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 ...
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  • 163
3 votes
0 answers
55 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 ...
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  • 151
3 votes
1 answer
126 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 ...
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2 votes
4 answers
137k views

Converting air flow rate between kg/s and m^3/s

Is 1 kg/s of air flow rate equivalent to 1 m3/s? I am calculating supply air flow rate into a zone for an air conditioning system. The simulation software gives the result in m3/s but the ...
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  • 161
2 votes
2 answers
83 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 ...
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2 votes
1 answer
1k 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 ...
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  • 170
2 votes
2 answers
100 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 ...
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2 votes
1 answer
589 views

Hydraulic switch vs heat exchanger

In a heating circuit, there's two (known to me) ways to decouple primary flow (through heat source) and the secondary flows (to consumers): a hydraulic switch in the heating manifold complete ...
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  • 4,643
2 votes
1 answer
27 views

Pressure loss of a shape change of an ar duct, keeping the area the same

I have an air duct 400x400 mm that will attach to an engine with a ventilation opening 981 x 167 mm. I assume a smooth funnel of about 500m length between the two shapes (that's about as much space as ...
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  • 4,643
2 votes
3 answers
2k 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 ...
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  • 97
2 votes
1 answer
133 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 ...
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  • 155
2 votes
0 answers
65 views

What would happen if the air conditioning failed in a skyscraper for an extended period?

I'm writing some fiction which involves the AC in a modern glass curtain skyscraper (50-80 floors?) in an American city failing for a period of weeks, maybe even for up to two months. Could anybody ...
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2 votes
0 answers
36 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 ...
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  • 2,402
2 votes
0 answers
25 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 ...
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  • 561
2 votes
0 answers
28 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 ...
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  • 21
2 votes
0 answers
111 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 ...
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1 vote
3 answers
71 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, ...
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  • 119
1 vote
2 answers
1k views

How can I turn home gas (LPG) from liquid to gas?

"LPG" is the term used here for a mixture of Propane & Butane sold for public use. The exact ratio varies depending on where you buy it and I think also with the season and is not known to me. I ...
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  • 143
1 vote
2 answers
898 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 ...
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