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Questions tagged [hvac]

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

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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. ...
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3answers
25 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 ...
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0answers
18 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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0answers
15 views

Ensure refrigerant lube return back to compressor

In Variable Refrigerant Flow system, valve box and indoor unit is placed soo much distance under the outdoor unit (compressor), sometimes in exceed of 90 ft. How they ensure lube oil in refrigerant ...
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1answer
43 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 ...
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1answer
139 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 ...
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0answers
12 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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2answers
60 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 ...
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1answer
32 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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1answer
57 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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3answers
431 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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0answers
28 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 ...
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3answers
169 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 ...
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0answers
50 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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2answers
218 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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0answers
28 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 ...
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1answer
38 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 = ...
2
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1answer
157 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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1answer
23 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 ...
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0answers
139 views

ASHRAE Duct Fitting Database References

For a brief time I had access to the "cloud" version of the ASHRAE duct fitting database. Before I lost access to the database, I intended to copy the list of all of the references from the "...
0
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1answer
59 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 ...
2
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2answers
50 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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2answers
1k 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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4answers
113 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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1answer
35 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 ...
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0answers
14 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 ...
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2answers
58 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 ...
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4answers
254 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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0answers
15 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 ...
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2answers
68 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)...
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1answer
38 views

How to measure velocity of hot gas ( temperature range: 100 - 450 ºC)?

I want to measure the velocity of hot gas coming out from an incinerator. The temperature can easily shoot upto 400-500ºC. I've checked online for hot-wire anemometers, even they claim to work in the ...
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0answers
97 views

Static Pressure of non-ducted fan

Is 0.0 the appropriate external static pressure to use when sizing a high flow exhaust fan that is not ducted on either the inlet or outlet? I can't find any specific guidance on this practice, yet I'...
4
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1answer
62 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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1answer
43 views

Has anyone achieved significant energy savings by increasing the cooling setpoints in retrofit office buildings, in practice?

I have a simulation based research vs. practical experience type question: There are a number of academic research papers available which claim 20% to 40% cooling energy savings by increasing the ...
6
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1answer
441 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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1answer
621 views

Fan BHP estimation

I need to provide an estimation of the BHP of a fan used in a HVAC system (water-source heat-pump). I have only limited information, the fan nameplate motor is 1 HP, it will run at 750 cfm is rated at ...
5
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2answers
86 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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2answers
94 views

Evaporative roof cooling

I have slightly inclined (50 cm over 6 meters) metal roof over my studio. The roof has bad thermal insluation -- 15 cm of mineral wool between sheet metal. The location is Kiev, Ukraine. Ambient ...
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3answers
6k 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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1answer
97 views

Can it be more efficient to pump heat into warmer water than cooler air?

About this time of year in my region people often look at the air conditioning compressor pumping heat to the outside air on one side of their house while their swimming pool heater tries to pump heat ...
1
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1answer
623 views

absorption refrigeration with low generator temperature?

I am IT engineer not a refrigeration expert, pardon my basic question. Would a NH3 or other absorption cycle work with a generator temperature of say 30C, and condenser temperature of 10C by ...
6
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1answer
388 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 ...
3
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2answers
57 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-...
6
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2answers
6k 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 ...
3
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2answers
173 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 ...
2
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1answer
248 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 ...
4
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1answer
790 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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2answers
864 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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1answer
152 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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3answers
8k 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 ...