Questions tagged [hvac]

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

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48 views

What is the efficiency of direct electric heating versus water heated via electricity?

I am attempting to keep plants warm in a greenhouse. Therefore, I assume that heating the soil should be most efficient, as that's what plants seem to care about the most (i.e. the temperature of the ...
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0answers
48 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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2answers
55 views

Can Peltier Modules be used as an Air Conditioner? [duplicate]

Air Conditioners are very expensive so I'm planning to build a split type air conditioner using Peltier modules for my sealed room that is 6.5 length, 7 feet height, and 5.6 wide. I plan to use nine ...
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50 views

Is the use of direct-expansion split systems to heat or cool exit enclosures permitted under the US model building Codes?

Most multistory buildings have enclosed exit stairways somewhere within them to provide safe egress from their non-discharge floors. In a building that relies on hydronic heating/cooling, steam ...
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26 views

HVAC Condensor Liquid Level/Ratio Estimate

Let's say I have a simple condenser inside of a HVAC system with 1 point of entry(Super-heated Vapour) and 1 point of exit(Saturated Liquid) for my refrigerant r134a. A pipe passes through it with ...
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1answer
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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32 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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1answer
51 views

What is the max speed and duty cycle of an air conditioner's magnetic clutch?

I am considering using an automobile ac compressor to control the resistance of an exercise machine by engaging and disengaging the magnetic clutch to let it slip. The max torque should be about 500 ...
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34 views

Would a Maisotsenko cycle evaporative cooler work more efficiently with a return air duct?

The "Coolerado M50" evaporative cooling unit uses a "Maisotsenko cycle" heat exchanger. It's installation instructions and all diagrams indicate air intake from external air only, ...
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30 views

Why does my heat pump condenser outlet make a single pass through the evaporator before the expansion valve?

I'm hoping to modify a hot water heat pump to capture both the hot and cold side. I'd work with an HVAC shop to make the modification but want to understand the circuit. It's not the simplest of units ...
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2answers
50 views

Cooling airflow calculation

I want to unplug my refrigerator in the winter, and cool it down by taking air from outside. The idea is to lead cool air from the outside through a pipe into the fridge, then let hot air out of the ...
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4answers
74 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 ...
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1answer
22 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, ...
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15 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 ...
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3answers
555 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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32 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 ...
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3answers
66 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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2answers
251 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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1answer
506 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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2answers
1k 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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79 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 ...
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0answers
27 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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2answers
48 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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0answers
43 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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1answer
29 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 ...
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1answer
86 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 ...
2
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1answer
5k 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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3answers
49 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
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0answers
23 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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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 ...
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1answer
68 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 ...
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0answers
13 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 ...
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3answers
218 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. ...
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3answers
46 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
27 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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2answers
1k 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
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 ...
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2answers
48 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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3answers
177 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
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1answer
109 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
103 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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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 ...
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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 ...
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3answers
3k 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
92 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
1k 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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53 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
87 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
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1answer
178 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
26 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 ...