ᐅ Assessment of the Heating Concept for a KfW 70 Energy-Efficient House
Created on: 6 Jan 2016 17:22
O
oerlein
Hello everyone,
I have already looked closely at the current offer we have for a KfW70 house and am not entirely sure about the air-to-water heat pump being used.
The following is currently included in the offer:
I have researched this heat pump online but cannot judge whether these are just some isolated negative experiences and satisfied users don’t speak up, or if the unit is actually that “poor.”
One significant concern for me was that the electric heating element activates already at around 0°C (32°F).
At a house viewing appointment, I was able to experience the heat pump, and despite it not being a very cold day, the outdoor unit seemed quite noisy to me.
What do you think about this combination/heat pump?
Are there alternative units you would recommend?
I am generally comfortable with the idea of an air-to-water heat pump, but those many negative impressions of the above Rotex unit have made me cautious.
Thank you very much for your support!
oerlein
I have already looked closely at the current offer we have for a KfW70 house and am not entirely sure about the air-to-water heat pump being used.
The following is currently included in the offer:
- KfW70 house
- 160 sqm (1,722 sq ft) of living space heated with underfloor heating
- central controlled ventilation system (manufacturer unknown)
- Rotex HPSU 6 compact heating and cooling with 500-liter (132-gallon) stratified storage tank up to 7 kW
I have researched this heat pump online but cannot judge whether these are just some isolated negative experiences and satisfied users don’t speak up, or if the unit is actually that “poor.”
One significant concern for me was that the electric heating element activates already at around 0°C (32°F).
At a house viewing appointment, I was able to experience the heat pump, and despite it not being a very cold day, the outdoor unit seemed quite noisy to me.
What do you think about this combination/heat pump?
Are there alternative units you would recommend?
I am generally comfortable with the idea of an air-to-water heat pump, but those many negative impressions of the above Rotex unit have made me cautious.
Thank you very much for your support!
oerlein
For maximum cost efficiency, hot water is omitted.
Your statement is theoretically entirely correct. In practice, however, it is nearly impossible for any homeowner to precisely predict their own usage patterns, as well as those of all other “residents.” Just consider: a couple or a family of three with a baby moves in, but 15 years later there is a small group of teenagers, living as five people, maybe with a grandmother added, making six in total. The eldest enjoys showering for 30 minutes straight with a high-pressure showerhead, the grandmother wants to take a full bath at least once a day, and every third day the small swimming pool is refilled.
A 500-liter (130-gallon) storage tank is not a bad choice, hygienically completely safe, and compared to the six-figure amounts involved in building a house, the higher operating costs are absolutely negligible.
Your statement is theoretically entirely correct. In practice, however, it is nearly impossible for any homeowner to precisely predict their own usage patterns, as well as those of all other “residents.” Just consider: a couple or a family of three with a baby moves in, but 15 years later there is a small group of teenagers, living as five people, maybe with a grandmother added, making six in total. The eldest enjoys showering for 30 minutes straight with a high-pressure showerhead, the grandmother wants to take a full bath at least once a day, and every third day the small swimming pool is refilled.
A 500-liter (130-gallon) storage tank is not a bad choice, hygienically completely safe, and compared to the six-figure amounts involved in building a house, the higher operating costs are absolutely negligible.
No, future user behavior is unknown. But you're exaggerating so much that it becomes impossible to plan anything for the house. Most people here know about the number of children and whether there is space for grandma. If you factor that in and think you need that much, and importantly, can afford it, why not. If your situation applies, though, 500 liters (13 gallons) is too small; when the pool is half full, the water heater is empty and your grandma has to wait 3 hours until it’s warm enough for her full bath. Since a house is expensive anyway, you can quickly buy your elderly care bed and put it in your later bedroom on the ground floor (just to exaggerate like you do). Just as a precaution, take 100 square meters (1,076 square feet) more house, a second washing machine, and leave the lights on at night—you might need it and those 30 euros per year with LED lighting are negligible anyway!
But seriously: for many, a 300-liter (79 gallons) water heater is more than enough, and often even has a reserve. As mentioned above, smaller tanks also recharge faster. Especially with heat pumps of lower capacity, this is an important factor.
If demand is that high, you need a larger heat pump anyway. With my ground-source heat pump, a smaller tank actually has an advantage because with shorter charging times, the ground temperature does not drop as much.
Otherwise, it can be said that this is basically a good appliance and it certainly works. Of course, you won’t really notice the extra cost of xx euros anyway—it’s missing from the start and continuously.
Oh, and regarding the annual performance factor: the 6 kW unit has a COP of almost exactly 3 at -7°C (19°F) outside temperature and 30°C (86°F) flow temperature, but only 1.8 at just 50°C (122°F). So, there is a noticeable difference in costs per kWh of heat output. At 20 cents per kWh of electricity, that is already a 5-cent difference, so you shouldn’t ignore the cold days.
But seriously: for many, a 300-liter (79 gallons) water heater is more than enough, and often even has a reserve. As mentioned above, smaller tanks also recharge faster. Especially with heat pumps of lower capacity, this is an important factor.
If demand is that high, you need a larger heat pump anyway. With my ground-source heat pump, a smaller tank actually has an advantage because with shorter charging times, the ground temperature does not drop as much.
Otherwise, it can be said that this is basically a good appliance and it certainly works. Of course, you won’t really notice the extra cost of xx euros anyway—it’s missing from the start and continuously.
Oh, and regarding the annual performance factor: the 6 kW unit has a COP of almost exactly 3 at -7°C (19°F) outside temperature and 30°C (86°F) flow temperature, but only 1.8 at just 50°C (122°F). So, there is a noticeable difference in costs per kWh of heat output. At 20 cents per kWh of electricity, that is already a 5-cent difference, so you shouldn’t ignore the cold days.
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