Hello everyone,
we are currently building – at the moment we are dealing with the heating system. Our energy consultant calculated the energy demand of our house (which is supposed to meet KfW 70 standards), and we took this information to the heating installer. We received an offer for a heating system that feels oversized to me.
My question/request at this point is whether anyone can assess if the system is reasonably sized or not...
According to the energy certificate, the house will have a final energy demand (per year) of 8.6 kWh/m² (2.7 kWh/ft²) for heating and 6.1 kWh/m² (1.9 kWh/ft²) for hot water. The building volume is just under 1000 m³ (35,315 ft³) and the usable floor area is given as 319 m² (3,434 ft²).
The heating system is supposed to be a brine/water heat pump (using deep geothermal boreholes) that heats via underfloor heating. An offer was made for a 14 kW heat pump...
Can anyone estimate from these values whether a 14 kW heat pump is correctly sized? Is it even possible for the heating installer to size the system based on this information, or are important details missing?
Thank you very much for your help!!!
Bonagel
we are currently building – at the moment we are dealing with the heating system. Our energy consultant calculated the energy demand of our house (which is supposed to meet KfW 70 standards), and we took this information to the heating installer. We received an offer for a heating system that feels oversized to me.
My question/request at this point is whether anyone can assess if the system is reasonably sized or not...
According to the energy certificate, the house will have a final energy demand (per year) of 8.6 kWh/m² (2.7 kWh/ft²) for heating and 6.1 kWh/m² (1.9 kWh/ft²) for hot water. The building volume is just under 1000 m³ (35,315 ft³) and the usable floor area is given as 319 m² (3,434 ft²).
The heating system is supposed to be a brine/water heat pump (using deep geothermal boreholes) that heats via underfloor heating. An offer was made for a 14 kW heat pump...
Can anyone estimate from these values whether a 14 kW heat pump is correctly sized? Is it even possible for the heating installer to size the system based on this information, or are important details missing?
Thank you very much for your help!!!
Bonagel
Bonagel schrieb:
...Our energy consultant calculated the energy demand of our house (which is supposed to meet KfW70 standards) – with this, we went to the heating installer. We received an offer for a heating system that, based on my gut feeling, seems oversized. I am fairly sure that the energy consultant prepared the Energy Saving Ordinance (EnEV) or KfW compliance certificate. Neither the actual energy demand nor the consumption can be derived from this. In fact, it is not allowed! Likewise, it is not permissible to design or size heating systems based on these results! Bonagel schrieb:
...My question/request at this point is whether anyone can assess if the system is plausibly sized or not... Certainly, no one can provide a reliable answer without thorough calculations beforehand. If the builder hasn’t done these, send them packing; otherwise, this could turn out to be a money pit. Best regards.
We have a similar "issue". Our heating installer offered us an Alpha-Innotec LWC 100 air-to-water heat pump with a heating capacity of 10 kW.
The heated area of the house, including partial basement heating, is 200 m² (2,150 ft²) with a room volume of 497 m³ (17,550 ft³). According to the energy certificate, our final energy demand is 22.2 kWh/m² per year. Our heating load calculation shows a standard heating load of 6.9 kW. We also plan to install a wood-burning stove, which will support us mainly in winter (besides its aesthetic appeal).
We still need to discuss with our heating installer why exactly this size of system is needed and not the LWC 80 with 8 kW.
My question to the experts here: when choosing a system, is an oversized heat pump more expensive than one that might be too small, requiring more frequent use of electric backup heating, especially when considering a few weeks of cold weather over the whole year? From what I have read, an oversized system also causes some additional costs.
The heated area of the house, including partial basement heating, is 200 m² (2,150 ft²) with a room volume of 497 m³ (17,550 ft³). According to the energy certificate, our final energy demand is 22.2 kWh/m² per year. Our heating load calculation shows a standard heating load of 6.9 kW. We also plan to install a wood-burning stove, which will support us mainly in winter (besides its aesthetic appeal).
We still need to discuss with our heating installer why exactly this size of system is needed and not the LWC 80 with 8 kW.
My question to the experts here: when choosing a system, is an oversized heat pump more expensive than one that might be too small, requiring more frequent use of electric backup heating, especially when considering a few weeks of cold weather over the whole year? From what I have read, an oversized system also causes some additional costs.
Orschel schrieb:
...Question to the experts here from me. When choosing, is an oversized system more expensive than a possibly undersized system where you have to use the electric heating element more often, especially when comparing a few weeks of cold weather to the entire year? From what I have read, an oversized system also causes some additional costs? Especially for air source heat pumps, the proper (matching) performance curve is crucial. Especially on/off units are no longer state of the art.If using an air source heat pump, fully modulating split systems are preferable whenever possible.
Besides the heating capacity curve, the COP curve is also important:
An undersized air source heat pump system provides insufficient heating power, causing the electric heating element to compensate excessively. An oversized system is also detrimental; on the one hand, its lifespan is limited by excessive cycling, and on the other hand, the seasonal performance factor tends to be rather poor.
The design effort required for ground source systems in sizing the heat source is comparable to the effort needed for evaluating the performance curves of air source heat pumps. With well-dimensioned systems, the electric heating element typically accounts for a maximum of about 2% of the annual heating demand.
Anyone neglecting these essential basics is very likely creating a money pit.
Best regards
NB: Performance figures for air source heat pumps cannot be compared directly with those of other heat generators!
Orschel schrieb:
I can tell this is a science in itself and not easy to calculate... Exactly, that’s why precise HVAC system planning and sizing is so important when aiming for high overall efficiency (low operating costs).
Best regards
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