ᐅ Challenges for MEP planners: underfloor heating flow temperature and wastewater ventilation
Created on: 15 Jul 2022 10:22
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Pacmansh
Hello,
we are at the beginning of the construction phase for our development project with the builder, and I am having some disagreements with the MEP planner. To be better prepared for the discussion, I would appreciate your assessment.
Point 1) Supply temperature of underfloor heating, new building, KfW55 standard, air-to-water heat pump
The supply temperature of the underfloor heating (end-terrace house on both floors) was stated to me as 40°C (104°F) after inquiry. This seems absurdly high to me. Additionally, I was informed that the surface temperature is designed to a maximum of 27°C (81°F) due to the flooring materials. Somehow, this does not seem consistent. When I asked about lowering the supply temperature, the response was: "A general reduction is not feasible with the underfloor heating without reducing the pipe spacing to an unacceptable level."
Do you have any ideas how I can respond to this in a reasonably professional way? Are there any documents or sources I could refer to, or information I should request?
Point 2) Wastewater venting
Contrary to earlier agreements, this has been planned in a rather unfavorable location. The reason given is "because the wastewater vent and the residential ventilation (exhaust air) must be routed over the roof with a certain separation according to flat roof guidelines." What distance should be maintained here? A quick online search only showed a 30cm (12 inches) distance to other building components. Basically, this is about the roof penetrations and their distance from each other, correct?
we are at the beginning of the construction phase for our development project with the builder, and I am having some disagreements with the MEP planner. To be better prepared for the discussion, I would appreciate your assessment.
Point 1) Supply temperature of underfloor heating, new building, KfW55 standard, air-to-water heat pump
The supply temperature of the underfloor heating (end-terrace house on both floors) was stated to me as 40°C (104°F) after inquiry. This seems absurdly high to me. Additionally, I was informed that the surface temperature is designed to a maximum of 27°C (81°F) due to the flooring materials. Somehow, this does not seem consistent. When I asked about lowering the supply temperature, the response was: "A general reduction is not feasible with the underfloor heating without reducing the pipe spacing to an unacceptable level."
Do you have any ideas how I can respond to this in a reasonably professional way? Are there any documents or sources I could refer to, or information I should request?
Point 2) Wastewater venting
Contrary to earlier agreements, this has been planned in a rather unfavorable location. The reason given is "because the wastewater vent and the residential ventilation (exhaust air) must be routed over the roof with a certain separation according to flat roof guidelines." What distance should be maintained here? A quick online search only showed a 30cm (12 inches) distance to other building components. Basically, this is about the roof penetrations and their distance from each other, correct?
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RotorMotor27 Sep 2022 17:23The information provided is too limited to offer proper advice.
We would need the room-by-room heating load, areas, and related details.
Perhaps there is a good reason why the heating demand is so high above.
Poorly insulated roof/ceiling?
Roof windows?
Other large north-facing windows?
Or calculation errors?
Otherwise, I cannot understand how one could assign 15 to the living room and 5 to the bedroom.
We would need the room-by-room heating load, areas, and related details.
Perhaps there is a good reason why the heating demand is so high above.
Poorly insulated roof/ceiling?
Roof windows?
Other large north-facing windows?
Or calculation errors?
Otherwise, I cannot understand how one could assign 15 to the living room and 5 to the bedroom.
I would already be satisfied with better advice than from the lady who is doing the calculation (she is at least the authorized officer at a large engineering firm).
It is a new build, a terraced house with a flat roof. Children's room 1 has only one south-facing exterior wall, children's room 2 faces south and east. The bathroom has a north-facing window. There are no roof windows. Therefore, only roof insulation or calculation errors are possible causes. Additionally, there is a central exhaust ventilation system with trickle vents, although these cannot explain the large difference between the children's rooms on the upper floor and the living area on the ground floor. I may be able to obtain the room-specific heating load directly through the developer. The planner is unwilling to provide this.
To approach the topic: The guest room on the ground floor (radiator length 83 m, valve size 15 cm (6 inches)) measures 10 m² (108 sq ft) and has two exterior walls; children's room 1 on the upper floor (2 radiators with 132 m and 138 m, valve size 5 cm (2 inches)) measures 12.7 m² (137 sq ft), has only one short exterior wall, and a similar window area.
It is a new build, a terraced house with a flat roof. Children's room 1 has only one south-facing exterior wall, children's room 2 faces south and east. The bathroom has a north-facing window. There are no roof windows. Therefore, only roof insulation or calculation errors are possible causes. Additionally, there is a central exhaust ventilation system with trickle vents, although these cannot explain the large difference between the children's rooms on the upper floor and the living area on the ground floor. I may be able to obtain the room-specific heating load directly through the developer. The planner is unwilling to provide this.
To approach the topic: The guest room on the ground floor (radiator length 83 m, valve size 15 cm (6 inches)) measures 10 m² (108 sq ft) and has two exterior walls; children's room 1 on the upper floor (2 radiators with 132 m and 138 m, valve size 5 cm (2 inches)) measures 12.7 m² (137 sq ft), has only one short exterior wall, and a similar window area.
The lengths of the heating circuit pipes vary too much. Very short ones can be combined, very long ones should be avoided. Without being particularly knowledgeable in fluid dynamics, the necessary hydraulic balancing then becomes a nightmare.
And why can’t a lower volume flow rate (VLT) be used? Is it not possible to enter a lower value into the old tool?
That’s something I would expect from a typical heating engineer who attended training 10 years ago, but not from an engineering office.
And why can’t a lower volume flow rate (VLT) be used? Is it not possible to enter a lower value into the old tool?
That’s something I would expect from a typical heating engineer who attended training 10 years ago, but not from an engineering office.
Joedreck schrieb:
And why can’t they calculate with a lower VLT? Apparently, the designer can't enter lower values into the old software?
I’d expect that from an average heating technician who had training 10 years ago, but not from an engineering firm. The work being done is really unacceptable. Their plan was probably just to calculate something, give it to the contractor, and be done with it. I guess they didn’t expect anyone to ask questions.
When they enter a lower supply air temperature, it results in a deficit in both children’s rooms. I can basically understand that, since the ventilation air is already at 5cm (2 inches). However, I don’t understand why the heating load in these rooms is so high.
It can really only be related to the ventilation system (central exhaust in bathrooms and kitchen, supply air through window frame vents). For example, I looked at the bathroom on the upper floor and children’s room 1. Both are on the upper floor, so the ceiling insulation is identical.
Bathroom: 9.5m² (102ft²), target temperature 22°C (72°F), heating circuit length 126m (413ft), ventilation air 5cm (2 inches)
Children’s room 1: 12.7m² (137ft²), target temperature 20°C (68°F), heating circuit length 132+138m (433+453ft), ventilation air 5cm (2 inches) (with 1 watt underperformance, so practically a perfect match).
This means that more than twice the heating pipe length is needed to get the children’s room to 20°C (68°F) compared to the bathroom for heating it to 22°C (72°F).
Pacmansh schrieb:
Bathroom: 9.5m² (102 ft²), target temperature 22°C (72°F), heating circuit length 126m (413 ft), pipe spacing 5cm (2 inches)
Children’s room 1: 12.7m² (137 ft²), target temperature 20°C (68°F), heating circuit lengths 132+138m (433+453 ft), pipe spacing 5cm (2 inches) (Here with 1 watt undercoverage, so almost spot on). Are these "straws" actually being installed? What diameter and wall thickness do the heating pipes have?
KfW55 and 38 degrees don’t quite seem to match.
I would design the bathroom for 23°C (73°F) down to -10°C (14°F). For possible lower temperatures, use electrical heating as backup. The supply temperature should then maybe be in the range of 30-32°C (86-90°F). The rest of the house would be straightforward then.
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Alessandro28 Sep 2022 11:25What is the total heating load of the building?
For KfW55 standard, it should not exceed 35 W/m². Something seems off...
Nowadays, all well-known heating manufacturers provide both heating load and installation calculations. They have software that can generate these within an hour. There is no need to hire a building services engineering firm for this.
For new buildings, the design temperature for the heating system is now usually set at 30°C (86°F) for natural ventilation.
For KfW55 standard, it should not exceed 35 W/m². Something seems off...
Nowadays, all well-known heating manufacturers provide both heating load and installation calculations. They have software that can generate these within an hour. There is no need to hire a building services engineering firm for this.
For new buildings, the design temperature for the heating system is now usually set at 30°C (86°F) for natural ventilation.
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