ᐅ Heat Load Calculation: Heating Demand Assessment according to DIN 12831 or DIN 4708?
Created on: 19 Mar 2014 11:14
L
Lacos
Hello everyone,
we are building a detached house (10.50m x 9m (34.4 ft x 29.5 ft)) and have received the energy demand calculation.
Since I am a complete beginner, I would like to ask for your help because the energy calculation seems a bit odd to me. Here are some details for better assessment:
- Gable roof, living area approx. 139m² (1495 ft²) (attic not developed)
- KfW 70 standard, cavity wall construction (total 46cm (18 inches)) with stagnant air layer
(sand-lime brick, insulation, air layer, facing brick)
- South-West orientation (no trees etc.)
- no mechanical ventilation system
- underfloor heating, geothermal energy (brine-water // deep drilling, Waterkotte Eco Touch B0/35=4.4)
Now to my questions:
1) It seems that the energy calculation was done according to DIN 4708.
Isn’t DIN 12831 already mandatory? Or optional? Can it be required for a new build?
What are roughly the differences between these standards?
2)
Calculated values:
Heating and cooling energy demand = 2.9 (domestic hot water) + 9.1 (heating) = 12 kWh/year
HT’ value W/(m²K) 0.30
QP kWh/(m²a) 38.9
-> The calculated heat demand seems a bit high for 139m² (1495 ft²) of heated area
(the attic, as mentioned, will not be developed). Do you see it the same way?
I would really appreciate your comments/feedback!
Thank you,
Lacos
we are building a detached house (10.50m x 9m (34.4 ft x 29.5 ft)) and have received the energy demand calculation.
Since I am a complete beginner, I would like to ask for your help because the energy calculation seems a bit odd to me. Here are some details for better assessment:
- Gable roof, living area approx. 139m² (1495 ft²) (attic not developed)
- KfW 70 standard, cavity wall construction (total 46cm (18 inches)) with stagnant air layer
(sand-lime brick, insulation, air layer, facing brick)
- South-West orientation (no trees etc.)
- no mechanical ventilation system
- underfloor heating, geothermal energy (brine-water // deep drilling, Waterkotte Eco Touch B0/35=4.4)
Now to my questions:
1) It seems that the energy calculation was done according to DIN 4708.
Isn’t DIN 12831 already mandatory? Or optional? Can it be required for a new build?
What are roughly the differences between these standards?
2)
Calculated values:
Heating and cooling energy demand = 2.9 (domestic hot water) + 9.1 (heating) = 12 kWh/year
HT’ value W/(m²K) 0.30
QP kWh/(m²a) 38.9
-> The calculated heat demand seems a bit high for 139m² (1495 ft²) of heated area
(the attic, as mentioned, will not be developed). Do you see it the same way?
I would really appreciate your comments/feedback!
Thank you,
Lacos
emer schrieb:
A quick question. If I want to have my heating system properly sized, I need to consult a certified energy consultant or an MEP (mechanical, electrical, plumbing) engineer, right?.. Less a certified energy consultant, this is the responsibility of an MEP engineer. Sometimes both roles are combined in one person! emer schrieb:
....On what basis do they calculate? Do I tell them the demand from my last utility bills, how often I take a bath, and how warm I like my rooms? Not for heating operation, because a new building has completely different demand requirements and necessities than a previous rental apartment! During planning, the desired room temperatures are taken into account! Form sheet V DIN 12831.
For domestic hot water, the usage requirements are also considered. Surely there is a difference between taking a weekly bath and having a football team shower every day.
Domestic hot water production must be planned just as carefully as the heating operation.
Recently, homeowners have often suffered from insufficient domestic hot water supply!
In the past, domestic hot water was often supplied alongside the heating system, which was usually feasible due to the high heating loads. Nowadays, thanks to energy saving regulations, times have changed significantly. For well to highly insulated buildings, it may sometimes make sense to separate the heat generation for heating and domestic hot water! A very typical case for passive houses based on PHPP!
I am currently reviewing two such cases. Apart from the excessively high consumption costs, homeowners in winter can choose whether they want hot water or the desired room temperatures.
Best regards
Hi,
to me, this all sounds somewhat unclear. It seems as if the energy performance certificate is not worth the paper it’s printed on.
What is the certificate actually good for – does it provide useful information or guidance regarding expected heating costs, for example (is a rough estimate like “very high heating costs per square meter” or “low heating costs per square meter” sufficient)?
What I’m really trying to do is to verify whether what I receive later actually corresponds to KfW 70 standards or if it has been “beautified” on paper. Is that impossible?
Of course, you would also have to check whether the building is constructed as described in the document, but that would be phase two.
Regards,
Lacos
to me, this all sounds somewhat unclear. It seems as if the energy performance certificate is not worth the paper it’s printed on.
What is the certificate actually good for – does it provide useful information or guidance regarding expected heating costs, for example (is a rough estimate like “very high heating costs per square meter” or “low heating costs per square meter” sufficient)?
What I’m really trying to do is to verify whether what I receive later actually corresponds to KfW 70 standards or if it has been “beautified” on paper. Is that impossible?
Of course, you would also have to check whether the building is constructed as described in the document, but that would be phase two.
Regards,
Lacos
Hello,
See above!
Since every building project is highly individual, a qualitative comparison is hardly possible. With the Energy Saving Ordinance / KfW, a standardization of certain boundary parameters was introduced to enable a qualitative comparison. What is actually needed/used later cannot be represented here! Therefore, I always calculate for my clients in advance what costs they can actually expect later! Since this happens in the preliminary planning phase, necessary changes can still be implemented easily and without major effort. Sometimes these are minor adjustments with little effort but significant impact.
Example: If the certificate specifies 35°C (95°F) flow temperature, night setback, no hot water circulation, insulation of pipes according to the Energy Saving Ordinance, etc., and these are not observed later during detailed planning or execution, the intended energy standard of the building and system is often violated. That would be an initial “whitewashing.”
Another example:
In new building certificates, a standard value of 0.05 is usually applied as a thermal bridge correction factor. However, this assumes that all thermal bridges are executed according to DIN 4108 Part 2. An equivalence proof is required here!
Looking at actual construction practice, this is often hardly the case!
Best regards,
PS: Why clients do not want to know in advance what consumption costs to expect later, yet sign contracts involving large sums, remains a mystery to me!
Lacos schrieb:That is not entirely correct. Both the Energy Saving Ordinance / KfW and EEWG certificates have their purpose. However, they can only be used as intended and prescribed by the legislator.
.... It sounds as if the energy performance certificate is not worth the paper it’s printed on..
See above!
Lacos schrieb:=> see above!
...What is the certificate actually good for - ....
Lacos schrieb:Qualitatively, yes. However, the objectives differ. The legislator focuses on primary energy, while the private builder has to pay for final energy!
....does it include useful statements/indications regarding expected heating costs etc. (just the granularity “very high heating costs/sqm, low heating costs/sqm” would suffice)?..
Since every building project is highly individual, a qualitative comparison is hardly possible. With the Energy Saving Ordinance / KfW, a standardization of certain boundary parameters was introduced to enable a qualitative comparison. What is actually needed/used later cannot be represented here! Therefore, I always calculate for my clients in advance what costs they can actually expect later! Since this happens in the preliminary planning phase, necessary changes can still be implemented easily and without major effort. Sometimes these are minor adjustments with little effort but significant impact.
Lacos schrieb:The Energy Saving Ordinance / KfW certificates should be understood as prior, overarching planning.
...what I am basically trying to do is check whether what I actually get afterwards corresponds to KFW70 or whether it was “cooked up”. Impossible?
Example: If the certificate specifies 35°C (95°F) flow temperature, night setback, no hot water circulation, insulation of pipes according to the Energy Saving Ordinance, etc., and these are not observed later during detailed planning or execution, the intended energy standard of the building and system is often violated. That would be an initial “whitewashing.”
Another example:
In new building certificates, a standard value of 0.05 is usually applied as a thermal bridge correction factor. However, this assumes that all thermal bridges are executed according to DIN 4108 Part 2. An equivalence proof is required here!
Looking at actual construction practice, this is often hardly the case!
Best regards,
PS: Why clients do not want to know in advance what consumption costs to expect later, yet sign contracts involving large sums, remains a mystery to me!
Hi everyone, hello Euro,
I noticed in the thermal insulation certification that an indoor target temperature of 19 degrees is assumed.
Is this a common basis for calculation?
Location "Germany", 50°00´ north latitude, region 0, annual average outside temperature Ta = 8.9°C (48°F)
Target indoor temperature = 19.0°C (66°F)
Regards,
Lacos
I noticed in the thermal insulation certification that an indoor target temperature of 19 degrees is assumed.
Is this a common basis for calculation?
Location "Germany", 50°00´ north latitude, region 0, annual average outside temperature Ta = 8.9°C (48°F)
Target indoor temperature = 19.0°C (66°F)
Regards,
Lacos
Hello,
For example, hot water:
According to the energy-saving ordinance/KfW, the demand is "preset" as 12.5 kWh/m²a (12.5 kWh/m²a) × An. An is a purely fictional area that has absolutely nothing to do with the actual heated living area!
The actual hot water demand depends on the number of people, the storage temperature, user habits, and so on.
Example: An = 200 m² (2150 ft²), hot water demand according to energy-saving ordinance => 2500 kWh/year.
Now the building may be occupied by 2 or 8 people. Under otherwise identical conditions, the following actual demand (not consumption!) might apply:
2 people: => 1360 kWh/year
8 people: => 5440 kWh/year
What use does the energy-saving ordinance/KfW certificate have then? None.
Heating: An identical building can be located either on Zugspitze or at the Lower Rhine! The system room temperature (RT) weighted geometrically by heating loads is 24°C (75°F) for one family and 21°C (70°F) for the other!
One family runs the heating ad libitum, the other heats continuously!
What use does the energy-saving ordinance/KfW certificate have then? None.
For determining actual conditions/requirements, only the component geometry and definition of the building envelope can be used from energy-saving ordinance/KfW certificates—nothing more!
Regards.
Lacos schrieb:Yes, because it is standardized and regulated alongside the other energy-saving ordinance parameters. However, energy-saving ordinance/KfW certificates have absolutely nothing to do with the actual conditions!!!
....Is this a common calculation basis?..
For example, hot water:
According to the energy-saving ordinance/KfW, the demand is "preset" as 12.5 kWh/m²a (12.5 kWh/m²a) × An. An is a purely fictional area that has absolutely nothing to do with the actual heated living area!
The actual hot water demand depends on the number of people, the storage temperature, user habits, and so on.
Example: An = 200 m² (2150 ft²), hot water demand according to energy-saving ordinance => 2500 kWh/year.
Now the building may be occupied by 2 or 8 people. Under otherwise identical conditions, the following actual demand (not consumption!) might apply:
2 people: => 1360 kWh/year
8 people: => 5440 kWh/year
What use does the energy-saving ordinance/KfW certificate have then? None.
Heating: An identical building can be located either on Zugspitze or at the Lower Rhine! The system room temperature (RT) weighted geometrically by heating loads is 24°C (75°F) for one family and 21°C (70°F) for the other!
One family runs the heating ad libitum, the other heats continuously!
What use does the energy-saving ordinance/KfW certificate have then? None.
For determining actual conditions/requirements, only the component geometry and definition of the building envelope can be used from energy-saving ordinance/KfW certificates—nothing more!
Regards.
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