Thermal insulation functions for water pipes
The thermal insulation of pipes, in heating and plumbing installations (water for human consumption, AFCH, and sanitary hot water, ACS) has the following fundamental objectives of Plumbing Newcastle.
- Reduce energy losses.
- Avoid superficial condensation.
- Reduce risks, avoiding accidental contact with hot surfaces.
- Reduce the risk of freezing pipes running through the exterior of buildings.
- Minimize the possible increase in temperature of water for human consumption.
- In addition, sometimes it also fulfills the mission of protecting the pipes from the aggression of construction materials and allowing their expansion.
Obviously, the necessary thickness will depend on the specific objective Reduction of heat losses
The fundamental object of Plumbing Newcastle thermal insulation is the reduction of heat losses and the minimum thickness is defined in IT 22.214.171.124.1. Of the Regulation of Thermal Installations in Buildings (RITE) published in Royal Decree 1,027 / 2007 of July 20, having entered into force on February 29, 2008.
In the aforementioned section, it is indicated that the pipes must be insulated when the water temperature is higher than 40 ° C and are installed in non-heated premises.
It also indicates that when they are located on the outside of buildings they must have sufficient protection against the elements and the insulation joints will be made in such a way as to prevent the passage of rainwater into the interior of the insulation.
Two procedures are defined for the selection of the minimum thickness of the pipe insulation:
The simplified procedure in which selection tables are given.
The alternative procedure, in which it must be justified that the thermal losses in the pipes will not exceed 4% of the maximum power transported.
In most installations, especially those with power less than 70 kW, the procedure to be applied will be the simplified one.
Minimum thickness of thermal insulation
The minimum insulation thickness is determined with the following parameters:
External diameter of the pipes:
Fixed the internal conditions of the water and external of the air, the greater the external diameter of the pipes, the greater the heat losses; therefore, a greater thickness of thermal insulation is required.
For a given pipeline, the higher the temperature of the fluid being transported, the greater the heat losses and, therefore, the greater the thickness of the insulation required.
Location of the pipes:
Those found on the outside of buildings have higher heat losses for two reasons:
Because the external temperatures are lower than those found inside the buildings are and because due to the speed of the wind, it has a higher coefficient of external convection; for this reason, the regulation imposes an increase in the thermal insulation of the pipes located outside the buildings.
Hours of operation of the installation: Obviously, energy losses depend directly on the number of hours of operation of the facilities, so the RITE establishes a higher thickness of thermal insulation for facilities that operate all year round, such as those of ACS.
Regardless of its mandatory nature, thermal insulation is convenient for the following reasons:
It ensures that the heat distribution is provided in the emitting elements, providing more precise control conditions, avoiding the increase in temperature of the premises when the regulation elements (such as thermostatic valves) have closed.
In underfloor distributions, thermal insulation avoids problems with pallets and floor finishing elements; this situation is very important in distributions with collectors that require a large number of pipes.
Avoid heat loss to other homes.
In these situations, the thickness of the insulation may be less than the minimum established in the previous table.
When heating distributions are seen, a common situation in existing homes where the distributions are usually worn above the baseboards, thermal insulation meets the requirement to avoid contact with hot surfaces that can cause accidents;
In IT, section 126.96.36.199.1. Indicates:
This requirement can be met with two solutions:
Place thermal insulation, it can be 10 mm, since its objective is to avoid high surface temperatures; this insulation can be incorporated into gutter solutions.
Design the entire installation to work with flow temperatures of 60 ° C, which forces to install larger radiators (it must practically double in size), this solution is best suited for condensing boilers.
Pipes of solar thermal installations
When selecting the thickness of the thermal insulation of the solar installations for ACS, the doubt arises as to which temperature is taken as a reference.
It is very common to propose what is known as stagnation temperature, which is usually around 200 ° C and corresponds to that which would be reached by the collector subjected to a radiation of 1,000 W / m2, with an ambient temperature of 30 ° C and with the installation stopped ( without extracting heat).
However, taking that temperature as a reference is an error, since in those situations it is interesting to dissipate as much heat as possible, so thermal insulation is not necessary; the thickness must correspond to the reference temperature of 60 ° C plus the 7 ° C of thermal jump between primary and secondary (67 ° C), obviously for external distributions.
Considering that the solar Plumbing Newcastle installation will operate in the hours of greatest radiation, in which the highest outdoor temperatures are available, a lower thickness of thermal insulation could be admitted, for example that corresponding to interior distributions; This is an aspect that should be clarified in the regulation itself, publishing a table for these applications.
The ACS facilities operate throughout the year, therefore, although in general their temperature may be lower than that of heating, throughout the season they present greater heat losses; for this reason the RITE increases the minimum thickness of its thermal insulation by 5 mm.