Rehau Insulpex Flexible energy transfer pipe for underground installations
Insulpex is specially designed for the efficient transfer of hot or cold water through buried insulated pipelines. INSULPEX consists of PEXa O2 Barrier pipe surrounded by a solid layer of CFC-free polyurethane foam insulation and an LDPE outer jacket.
INSULPEX is available in one- and two-pipe configurations. The two-pipe configuration combines return and supply pipes, for even faster installations. Sold in 100 ft coils, Free Shipping
5.1. Trench Installation
Do not install INSULPEX in soil or groundwater conditions which are thought or known to be contaminated with fuels, organic compound, solvents or other possible hazards, as these sub- stances could permeate the pipe and contaminate the water or damage the integrity of the pipe. If contamination is suspected, a chemical analysis of the soil or groundwater must be performed to determine the contaminant and its compatibility with INSUL- PEX.
A minimum of 4 in (10 cm) of sand should surround INSULPEX in the trench. The sand protects the INSULPEX from sharp objects and is crucial to the thermal compensation of the system.
Native soil can be used for the remaining fill, as long as there are no large (greater than 1 1/2 in [4 cm]), frozen or sharp objects such as rocks or debris. Compact the fill material by hand to a height of at least 6 in (15 cm) above the INSULPEX. Above the hand-compacted fill, a mechanical device can be used to com- pact the soil.
INSULPEX is suitable for H-20 loading at depths ranging from 2 ft (60 cm) from the roadbed to a maximum 8.5 ft (260 cm). See Figs. 5.1 and 5.2 for H-20 trench dimensions.
For applications where loading is not a concern, the trench
depth should be a minimum of 16 in (40 cm). For better thermal performance an increased burial depth is recommended. Burying the pipe below the frost line can prevent heaving and improve thermal performance.
5.4 Thermal Expansion
5.2 Above-Ground Installation
Above ground installations of INSULPEX (protected from direct exposure to UV radiation) must be properly supported with either fixed or sliding supports. Local code may define the maximum distances between support devices, otherwise, horizontal and vertical runs should be supported every 40 in (1 m). INSULPEX may not be used for permanent, unsheltered outdoor exposure.
5.2.1 Fixed Supports
Fixed supports are typically applied at fitting locations. When using a fixed support, follow the support manufacturer’s recom- mendation for installation. Place the fixed support on the body of the fitting, not on the INSULPEX jacket nor on the SDR11 compression sleeve.
5.2.2 Sliding Support Device
To allow for expansion and contraction, support devices for INSULPEX should allow for movement with slide linings. Support devices must accommodate the outside diameter of INSULPEX and not squeeze the pipe unnecessarily. Make sure the mate- rial contacting the INSULPEX is not abrasive and does not allow sharp edges to protrude into the INSULPEX. The installer should place 3 sliding supports at 90° bends, observing the minimum bend radius.
5.3 Building Penetration
For penetrating through an exterior wall there are two options, bored hole and wall breakthrough. Both options require the use of the wall sealing ring and require filling in the hole with con- crete.
For a wall breakthrough make an opening with the dimensions from Table 5.3.
For bored holes make hole(s) with the dimensions from Table 5.4.
Linked-type sealing rings suitable for polymer pipes can also be used when following manufacturer’s instructions. Linked seals do not use mortar and do not require a wall sealing ring, however the bored hole should still be sealed as described above
The unique property of INSULPEX is that it is self-compensating when buried in accordance with the instructions in the REHAU INSULPEX Installation Guide. The friction force between the fill sand around the INSULPEX and the outer casing is sufficient to limit thermal expansion of the pipe under typical operating condi- tions.
However, when INSULPEX is installed in a non-buried applica- tion, the system design must account for the natural tendency of the pipe to expand due to temperature change.
5.5 Transition to Building Service Piping
To keep the thermal expansion within acceptable limits when connecting to a building, INSULPEX pipes should not extend beyond the exterior wall into the building more than the distances specified in Table 5.5. If the end caps are fully inside the wall, these distances can be reduced by 2.3 in (6 cm). The PEXa car- rier pipe requires properly designed and installed fixed brackets inside the building suitable for the thermal expansion forces.Fixed brackets may be attached to the fitting body, but not to the SDR11 compression sleeve.
The detailed descriptions that follow are expressed in terms of heat load and heat loss, however the same principles and proce- dures apply to cooling loads and heat gains.
This section outlines the procedures required for a complete INSULPEX system design. A full analysis of system performance and requirements involves the following design elements:
– INSULPEX length determination
– Total heat load estimation
– Flow rate estimation
– INSULPEX size determination
– INSULPEX heat loss calculation
– INSULPEX pressure loss calculation
6.1 Step 1: Determine Length
end), if using the RAUTOOL G2 toolkit.Fig. 6.1: Tool clearance
– Calculate the distance of the INSULPEX route in feet. When planning the route, be sure to check with utility companies and other trades to account for obstructions.
– Add 4.5 ft (1.4 m) of length for every 90° bend in the pipe.
– Be sure to account for both the supply and return legs of the
route if you are not using two-pipe INSULPEX.
– Ensure there is at least 20 in (51 cm) of clearance (from pipe
13 ft (4 m) or more
Observe the minimum bend radii listed in Chapter 4. If a coupling or tee connection must be placed on a bend, ensure that the radius is
Fig. 6.2: Bend radius at connection
L = 800 ft (400 ft supply + 400 ft return) qtot = 600,000 + 10 x 800 = 608,000 Btu/h.
6.2 Step 2: Estimate Total Heat Load
A system heat load calculation should take into account heat lost through the INSULPEX pipe. An initial rough estimate of the total heat loss can be obtained by using:
qtot = qload +10(Btu/h ft) x L
This assumes a loss of 10 Btu/h per foot of pipe, based on: – Average INSULPEX size
– Tave of 135°F, Tsoil of 50°F
– Medium soil thermal conductivity condition
qload = 600,000 Btu/h
6.3 Step 3: Estimate Flow Rate
Having estimated the total heat load, qtot the designer may proceed with the flow rate (where 60 converts hours to minutes) estimation by using:
USGPM = qtot/(ρ x Cp x 60 x ∆T)
The designer of the heating system should provide the ∆T. This equation calculates the required flow rate of the heating fluid in the INSULPEX based on fluid properties and desired ∆T.
Example continues, given:
qtot = 608,000 Btu/h
∆T = 35°F
Water as a heating fluid
(ρ = 8.22 lb/gallon, Cp = 1 Btu/lb·°F @ 135°F [57°C])
(608,000 Btu/h)/(8.22 lb/gallon x 1 Btu/lb °F x 60 min/hr x 35°F) = 35 gpm
Note: If the heating fluid includes antifreeze, be sure to use the correct values of density and specific heat corresponding to
the type and concentration of antifreeze in the water. Table 6.1 shows the combined properties of common heating fluid mixtures and concentrations.
6.4 Step 4: Determine Pipe Size
Correct sizing of the system pump(s) and other components requires selection of the appropriate INSULPEX carrier pipe size. The
INSULPEX pipe should be chosen based on the estimated
flow rate and the resulting head loss (see REHAU PEXa Piping Systems
Pressure Loss Tables). The suggested range of head loss through the pipe is 10 to 20 ft of head. Additional losses through system components must be taken into account when sizing pump(s) and other equipment.
Rtot: Total Thermal Resistance
qtot = 600,000 + (135 - 50) x 800/8.0 = 608,500 Btu/h
The total thermal resistance must be determined, see Table 6.3. The following variables must be determined to derive an accurate Rtot value:
– Db: Depth of Bury to Pipe Centerline
Determine the depth from the top of the trench to the horizon-
tal centerline of the pipe(s) in inches. – Soil Type
Thermal conductivity of the soil depends on factors such as soil composition, particle size and nature, water and air con- tent and drainage. For the purposes of this heat loss calcula- tion, we will
classify three kinds of soil, shown in Table 6.2.
Note: The REHAU INSULPEX Installation Guide states that the trench should be filled with sand around the INSULPEX. However, for the purposes of the calculation, soil type selection should be based on the native soil properties.
Once the heat loss through the INSULPEX is known, calculate a more precise total heat load by using:
qtot = qload + qINS
Compare this to the qtot estimated in the total heat load estima- tion. If the values differ by more than 5%, use the new qtot to calculate a corrected flow rate. Then, using the new flow rate, verify that the appropriate pipe size has been chosen.
Example continues, given: INSULPEX 63 mm
Db = 39 in. to centerline Rtot/L of 8.0 h·ft·°F/Btu
6.6 Step 6: Calculate Head Loss
The design must ensure the flow requirement and pressure loss are within the circulator’s performance capability. To express pressure loss in feet of head, multiply by 2.307.
Refer to the pressure tables to calculate the pressure loss of the fluid in the INSULPEX pipes. Find the table that corresponds most closely to the amount of glycol in the fluid, if any. Find the intersection of the row corresponding to the flow rate of the fluid, and the column of the correct fluid temperature and pipe size. The number at the intersection is the psi loss per 100 ft of INSULPEX pipe. Multiply that number by the number of 100’s of feet of pipe in the system, as shown:
Example continues, given:
0.89 psi loss per 100 ft @ Tave = 120°F 0.79 psi loss per 100 ft @ Tave = 180°F
Through linear interpolation this calculates to: 0.85 psi loss per 100 ft @ Tave = 135°F
Pressure loss = 0.85 x 8 = 6.8 psi
Additional sizes available up to 2-1/4". For additional pricing on PEX tubing, please call (406) 300-1776 for assistance.
The most critical points in a pre-insulated PEXa piping system design are:
– To ensure the flow requirement and pressure loss are within the circulator's performance capability.
– To design the buried depth to use energy efficiently and to avoid heaving of the pipe in the coldest months.
– To transition to building service piping immediately upon enter- ing the building and to properly secure the transition fitting.
In view of the increasing need to minimize CO2 emissions as much as possible, local heating supply technology is becom- ing increasingly important. Pioneering technologies, combining optimal functionality with low energy losses, are the basis for REHAU INSULPEX pre-insulated PEXa piping systems.
3.1 System Advantages
INSULPEX is flexible, pre-insulated PEXa piping with closed-cell polyurethane (PU) foam bonded insulation.
– Flexible pipe system ensures cost-effective heat distribution
– Minimal linear expansion, as pipe layers are fully bonded
– No need for expansion bellows or compensators
– Fully bonded pipe layers limit water penetration to absolute
– System components for a variety of applications
INSULPEX is used predominantly below ground and is ideal for applications including:
− District heating
− Energy transfer
− Snow and ice melting − Chilled water
− Process piping
− Hydronic piping
− Industrial and agricultural − Outdoor wood furnace
Insulpex pipe consists of O2 Barrier PEXa pipe encased in closed-cell polyurethane (PUR) foam insulation, with a protective low-density polyethylene (PE) outer casing. O2 Barrier pipe is made of high-quality crosslinked polyethylene, manufactured using the high-pressure peroxide method (PEXa). O2 Barrier pipe has a co-extruded oxygen diffusion layer that complies with the requirements of DIN 4726. O2 Barrier pipe is manufactured by REHAU in a plant using a quality management system that is certified to ISO 9001.
Insulpex pipe meets the requirements of DIN 16892 and 16893. The size listed in the description is the nominal diameter in millimeters, according to DIN 16893. Metric pipes are SDR11 and are compatible with SDR11 compression-sleeve fittings. Refer to Insulpex Technical Manual (Art. 855.630) for pipe dimension details, capacities and temperature/pressure ratings.