How to measure the freezing of walls with a pyrometer

Pyrometers are often used by experts as additional equipment when a complex television inspection of a building is being carried out. But to search for heat loss, such “infrared” devices can be used independently.

What could be the problems
External walls, basement and attic floors, roofing, windows / doors – these enclosing structures make up the heat-shielding shell of the building. A properly organized heat-shielding shell should protect the heated volume of the building from excessive heat loss.

But sometimes this circuit is broken if there is damage to the thermal insulation, bridges of cold or blowing appear. And sometimes the thermal envelope is quite homogeneous, but it easily passes thermal energy through itself over the entire surface – this happens when the insulation is completely absent, has insufficient thickness, or for some reason has lost its working properties … In such cases, heating costs turn out to be too high.

There is another problem – the manifestation of the so-called “dew point”. It looks like this: at a certain temperature and with a redistributed relative humidity, water vapor contained in the air settles on objects and structures in the form of condensate.

The table below shows the zone with the dew point temperature typical for apartments and private houses (air temperature and standard relative humidity for residential premises are taken into account). Suppose the temperature in your kitchen is about 22 degrees, and the humidity is 60 percent. According to the numbers from the table, it becomes clear that if the inner surface of the street wall in some place has a temperature of 13.9 degrees or less, then condensation may occur on it.

As a result, we can observe “weeping windows and slopes”, freezing of external walls (including with the appearance of frost), wetting of corners, as well as a riot of mold and fungi that need life-giving moisture to flourish. And this is just the tip of the iceberg. The elements of the house that are invisible to us suffer greatly from unaccounted for moisture: steel rusts, lumber rots and warps, mineral building materials swell and gradually dissolve. And most importantly, there is a threat to the health of residents …

If the insulation gets wet, the water displaces air in it, which is the main insulator of thermal energy. Therefore, thermal insulation greatly loses its properties (for example, it has been proven that 5% moisture content of mineral wool reduces its thermal performance by half), and the situation is only getting worse.

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From problems to solutions
First of all, you need to use a pyrometer (or thermal imager) to find vulnerabilities through which precious heat escapes most intensively, and try to determine the degree of heat loss. Knowing the problem, you can begin to neutralize it.

It makes sense to inspect the places through which heat leaks most often occur with the help of pyrometers / thermal imagers regularly – once a year, for example. The fact is that building materials are able to “degrade” over time and resist heat transfer less (for example, polyurethane foam and sheet polystyrene foam can be destroyed under the influence of ultraviolet radiation, and fibers can be weathered from mineral wool under the action of convective currents, which leads to a loss of its density) .

Sometimes a thermal engineering survey is carried out in houses that are still under construction in order to be able to make adjustments to the design and get out of a difficult situation at low cost. To do this, they close window openings and use devices that pump excess pressure inside the building with a powerful fan (the so-called “air doors”). Then a pyrometer or a thermal imager comes into play.

How does a pyrometer help?
Heat transfer forces act on the materials and structures of a building. In the cold season, we have two separate environments: the frosty air outside and the space of the building heated by artificial heat sources. In heated rooms, increased pressure naturally occurs, due to which the thermal energy tends to go outside, while the building envelope cools noticeably. The higher the heat transfer resistance of the walls (or other elements of the house), the less they freeze through. In fact, this process can be imagined as a kind of tug-of-war.

As a result, from the side of the street, one can observe how heat escapes in defective areas, heating the surfaces. We will be primarily interested in areas with high temperatures.

And from the side of the premises, the situation will be diametrically opposite – defective areas are clearly visible from the anomalous cooling of local zones.

Why a pyrometer and not a thermal imager
In a sense, the pyrometer can be considered a prototype of the thermal imager. A thermal imager also works with infrared radiation, but unlike a pyrometer, it not only gives the temperature at the aiming point, but also can display and save thermograms on the screen – very informative contrasting pictures. But even the most inexpensive thermal imagers connected to a smartphone (for example, the Seek Thermal Compact model ) now cost at least 23,000 rubles, while the price of a “household” pyrometer starts at 1,400 rubles.

Yes, it will take more time. Yes, they will not give that impressive visibility as thermal imagers. However, pyrometers will easily indicate temperature anomalies in building envelopes. With the correct use of the device, it will be no less accurate and the same “non-destructive” control.

 

How to prepare for measurements
When is the best time to measure? As in the case of using a thermal imager, it is best to determine the heat loss with a pyrometer at the maximum difference between outdoor and room temperatures. However, in GOSTs, a thermal audit is recommended to be carried out in the autumn-spring heating period. The temperature difference must be at least 10 degrees.

Measure outside or inside? The survey will be most informative if you measure the building envelope on both sides. In practice, if you own not a one-story cottage and not an apartment on the ground floor, it will be extremely difficult to maintain the same distance to all shooting areas from the street side. In addition, various suspended structures, such as siding or block house sheathing, can become an insurmountable obstacle to accessing the walls from the outside.

Weather. You can start working with the pyrometer from the side of the street in the absence of precipitation, as well as smoke and fog. For the survey, be sure to choose a time with a minimum wind force.

Choice of time of day. It is advisable to search for heat loss with a pyrometer in the morning, when direct sunlight does not fall on the examined surfaces, which can heat the materials and distort information about the actual surface temperature. Evening is not the best option, since the walls can accumulate some amount of heat, although by the time of the examination they are no longer exposed to the sun.

Stabilization of indoor temperature. If this is a private house in which people stay from time to time, then the object must be heated for at least 3 days before measurements so that all elements of the building warm up. In any case, windows and doors at the facility are recommended to be kept closed for 12 hours.

Unhindered access to building envelopes. When measuring from the side of the street, frost and snow must be removed from the surfaces. When working indoors, you will have to remove paintings and carpets from the outer walls, move furniture away. The pyrometer will not be able to “finish off” to the wall if peeled wallpaper or some kind of pollution is in the path of its beam – it works exclusively on surfaces, in “line of sight” conditions. Also, experienced professionals strongly recommend dismantling the skirting boards on the outer wall and partially on the walls adjacent to it. If the task is to determine the heat loss in a private house, then access to the attic and basement will be needed.

 

Measurement procedure
1. First of all, it is necessary to draw up diagrams of the measured surfaces. You may need some detailed drawings of individual components of the house (for example, it makes sense to separately depict window openings with slopes and window sills that are very vulnerable to heat loss), on which you can record the temperature readings of the pyrometer. For maximum clarity, it is advisable to use a camera in conjunction with a pyrometer . There are no special requirements for photographic equipment, the main thing is to be able to identify the control area from the photo, so you can use a smartphone .

2. It is desirable to create a “logbook” in which it will be possible to record data on survey conditions (wind speed, air temperature, humidity, distance to surfaces, precipitation, time/date). It will help to take into account these nuances during repeated examinations, so that you can correctly compare the results.

3. It is necessary to determine the examination scheme and then strictly adhere to it. For example, divide the wall into conditional small zones and work them out according to the “bottom-up, right-left” principle.

4. It is recommended to inspect the enclosing structures. We have to work blindly with a pyrometer (unlike a thermal imager, which first makes a large survey thermogram), so preliminary visual detection of defects will help us a lot: condensate, moldy surfaces, frozen areas with frost that has come out, peeled wallpaper, darkened putty, loose brick …

5. We choose the distance at which we will perform the survey (and then we try to maintain it in all zones). When using the pyrometer indoors, there are no problems – a distance to the surface of 1-1.5 meters will be optimal. But on the street, when you need to examine the walls of a two-story cottage, you won’t be able to get closer. Therefore, it is necessary to take into account the optical resolution of the device (with increasing distance, the area of ​​the spot of the examined surface and the error increase). For such work it is necessary to use pyrometers with an optical resolution of 12:1 and higher . But even such a technological device from a distance of 6 meters will irradiate a spot with a diameter of about half a meter, therefore, in order to obtain more accurate indicators, it is better to find an opportunity to reduce this distance.