The hottest f971 application to solve the problem

2022-07-28
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F971 application - solve the problem of humidity in residential buildings

measuring tools: temperature and humidity meter, pipe clamp probe, IR thermometer, digital multimeter

the test item "guidance" stipulates: relative humidity, wet bulb temperature, dew point, overheating

background: single-stage residential refrigeration equipment. The homeowner complained that the humidity was too high at the desired automatic constant temperature setting

observation: the house is a low bungalow; The air handling unit and piping system are located in the attic; Concrete structure; Indoor carpeting; The temperature is set at 74 ° f; The air conditioning system was installed last summer, and the load is calculated according to the ACCA best method in the "mixed/wet" temperature zone

action: you may think this is too simple: it may be a system related problem (dust filter, low voltage, dirty condenser, etc.). But you also realize that the weather was cooler than most summers. You measured the indoor temperature and relative humidity and found that the temperature and humidity were 74.5 ° F, 68% RH, 66 ° f WB, 63.3 ° f DP*

you think the problem is related to the following reasons: the weather is cooler than usual in summer, the equipment has less working hours (less humid air is discharged), the carpet on the concrete will hide the humid gas and form an environment conducive to the breeding of fungi. You also want to know whether there is a sand layer that can keep moisture between the damp proof course and the concrete floor, which will aggravate the moisture problem under the carpet

using fluke 60 series infrared thermometer to measure the carpeted ground, the measured temperature is 68 ° F. The temperature is higher than the dew point. According to the temperature humidity diagram, the water vapor pressure in the carpet is higher than that in the air, so the moisture will flow from the carpet to the air. This is good for carpets, but will result in higher relative humidity in the living space. Since it is easier to deal with the relative humidity than the humidity of the ground, this is more advantageous

you ask the homeowner if he has ever renovated his house. They say, "No. wait, we have installed a new roof. Does that count?" You asked: "the roof with the same structure?" They said, "yes, but we changed green to white." You said, "thank you. I also noticed that you keep the fan on. Is there any reason?" "We think that will keep the air flowing and make the house more comfortable," they said You think you should comment after collecting the data

outdoors, you use fluke 971 relative humidity meter to measure parameters of 80 ° F, 76% RH, 74 ° f WB, 71.8 ° f DP. When you think about the attic, you worry about the dew point. You checked the condenser, which is your trusted model and works properly (according to the indoor 66 ° f WB and outdoor 80 ° f DP). According to the intake meter of the throttle valve, the overheating of the suction pipe should be 18 ° F. You confirmed this with fluke 80pk-8 clamp temperature probe

you are back indoors again. When you climb to the attic to check the air handling unit (80 afue gas stove), you still think that the light color roof will reduce the temperature and heat absorption of the attic compared with the dark color roof. Not only will this reduce operating hours, but lower attic temperatures will increase the chance of condensation in air supply lines and air handling units, especially at 72 ° f DP. The temperature in the attic is 108 ° F. Good, not too cold. You looked at the piping system, the furnace, and the horizontal evaporator. You used an infrared thermometer to scan the pipe wrapping on the aluminum foil. When you see an average temperature of 76 ° F, you are relieved. Wait, at a distance of 6 feet from the air handling unit, the temperature measured by infrared is 72 ° F. if you get closer, you will feel very wet

when you open the insulation layer, you find that one of the pipe joints is not welded well. This can explain why the vanadium battery is facing a huge cost pressure drop at this temperature. You rewelded the joints, wrapped the insulation, and resealed the cadmium layer. So far, the problem has been solved before it becomes more serious. You are sure that the aluminum foil veneer can remain above the dew point, and turn your attention to the problem of indoor relative humidity

the filter is relatively clean. You reinstall it and check the evaporator. The evaporator is also clean, but not horizontal. The water at the back of the water pan should be higher than the front drainage position. You are very lucky. The evaporator and the stove are connected together by basket screws. You adjusted the basket screws to achieve the best drainage. This will help prevent moisture from being sucked back into the air flow during the shutdown cycle, but you want to use a TXV (thermal expansion valve) instead of a fixed flow limiting device for the evaporator, because you know that TXV can provide better performance under partial load

optional actions:

now, you need to determine what actions to take to improve performance under partial load conditions

1. The performance has been preliminarily improved by re arranging the condenser water pan to better drain water

2. It is recommended that the owner keep the fan in the "automatic" state to reduce the re absorption of moisture during the shutdown cycle

3. You tell them to use an electronic thermostat of the best quality, which can adjust the temperature difference setting. You decide to change the temperature difference from 1 ° f to 1.5 ° f to make the opening time longer and obtain more stable dehumidification time

4. You use the fluke digital multimeter and two 80pk-26 universal temperature probes to measure that the delta-T of the evaporator is 18 ° F. You can reduce the air supply speed, but you cannot determine the temperature of the pipe surface under other operating conditions

5. Use TXV instead of fixed flow limiting valve

6. The straight evaporator is used to replace the wavy evaporator, so that the spacing between the heat sinks is larger. Because the wavy fins store more water, and the smaller the fin spacing, the more water

measures 1, 2 and 3 were taken. Since the equipment is not very large, you think it will produce the expected results. Measure 4 makes you uneasy. You don't know whether you need further improvement. You can try it. You do not want to take measures 5 and 6, which inevitably leads to a discussion about costs

now it's time to explain to the owner...

"you feel that the indoor humidity is very high

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