ᐅ Domestic Hot Water Heating vs. Air-to-Water Heat Pump Efficiency
Created on: 8 Sep 2014 15:53
C
cmsgarb
Hello everyone,
We have been living in our new house for about three months, which is equipped with an air-to-water heat pump that also heats the domestic hot water. There is a buffer tank maintained at 50°C (122°F) and a fresh water station that heats the hot water on demand. The heat pump is currently in summer mode, meaning the circulation pump for the underfloor heating is off, and the heat pump is only heating the water. For the past two months, I have been tracking the electrical energy consumed as well as the heat produced to get a sense of the heat pump’s efficiency, and I am a bit surprised. Typically, in our household of three people, we use about 5 kWh of electricity per day and get around 11 to 12 kWh recorded by the heat meter. That means a ratio of 2.2 to 2.4 times energy output. I expected higher efficiency since the heat pump brochure mentions a COP of up to 5 at 20°C (68°F) outdoor temperature, but that is at a supply temperature below 40°C (104°F).
So, my questions are: what is your energy consumption for domestic hot water generation in a three-person household? Is it also around 5 to 6 kWh? And does anyone have experience and can help me understand where my reasoning about efficiency might be wrong? Could it be that the electric heater is already being used to reach the 50°C (122°F) buffer tank temperature?
Best regards,
Christian
We have been living in our new house for about three months, which is equipped with an air-to-water heat pump that also heats the domestic hot water. There is a buffer tank maintained at 50°C (122°F) and a fresh water station that heats the hot water on demand. The heat pump is currently in summer mode, meaning the circulation pump for the underfloor heating is off, and the heat pump is only heating the water. For the past two months, I have been tracking the electrical energy consumed as well as the heat produced to get a sense of the heat pump’s efficiency, and I am a bit surprised. Typically, in our household of three people, we use about 5 kWh of electricity per day and get around 11 to 12 kWh recorded by the heat meter. That means a ratio of 2.2 to 2.4 times energy output. I expected higher efficiency since the heat pump brochure mentions a COP of up to 5 at 20°C (68°F) outdoor temperature, but that is at a supply temperature below 40°C (104°F).
So, my questions are: what is your energy consumption for domestic hot water generation in a three-person household? Is it also around 5 to 6 kWh? And does anyone have experience and can help me understand where my reasoning about efficiency might be wrong? Could it be that the electric heater is already being used to reach the 50°C (122°F) buffer tank temperature?
Best regards,
Christian
D
Doc.Schnaggls9 Sep 2014 14:02I am neither an HVAC engineer nor employed or registered in this field.
However, I have never claimed to be.
Nonetheless, my posts always contain my unconditional experiences and/or knowledge, which I share freely with other readers in the forum.
However, I have never claimed to be.
Nonetheless, my posts always contain my unconditional experiences and/or knowledge, which I share freely with other readers in the forum.
Doc.Schnaggls schrieb:
...However, my posts always include my full experience and/or knowledge, which I share with the other forum readers free of charge. This is certainly commendable, but outside the specific conditions of your construction project, it is simply not applicable at all!!!! There is a lack of comprehensive, responsible professional expertise here! In other words, what makes sense and is effective for you, under other specific circumstances, might well turn into a costly failure!
Are you aware of this and can you professionally assess and take responsibility for it?
Hello Wastl, hello Perlenmann,
Thank you for the figures as a reference. Regarding the set temperatures, these are the values configured by the heat pump manufacturer’s installer. We currently reach a maximum temperature of about 45°C (113°F) in the shower water, so it should be possible to reduce it by 5°C (9°F).
Best regards
Christian
Thank you for the figures as a reference. Regarding the set temperatures, these are the values configured by the heat pump manufacturer’s installer. We currently reach a maximum temperature of about 45°C (113°F) in the shower water, so it should be possible to reduce it by 5°C (9°F).
Best regards
Christian
D
Doc.Schnaggls9 Sep 2014 15:17€uro schrieb:
That may be honorable, but outside the specific conditions of your building project, it is simply not applicable!!!! There is a lack of comprehensive, responsible professional expertise here!
In other words, what makes sense and is effective for you could, under different specific conditions, turn into a costly disaster!
Are you aware of this and can you professionally assess and take responsibility for it?Sorry, €uro, but I don’t have time for such unproductive "rambling."
I am capable of looking beyond my own field and do not limit myself to my area of expertise when I share experiences as a homeowner.
The purpose of my posts in this forum is definitely not to threaten other members with financial disasters to secure lucrative contracts for myself.
Also, I am not the type to receive yellow or red cards in other forums.
Find someone else who will engage with you in pointless discussions.
cmsgarb schrieb:
which is equipped with an air-to-water heat pump that also heats the domestic hot water. For this purpose, there is a buffer tank maintained at 50°C (122°F) and a fresh water station that then heats the hot water.I'm too stupid, I don't understand.
What is the purpose of the fresh water station if there is a buffer tank for domestic hot water heated by the heat pump?
Regarding the question about hot water consumption: 1.3 kW, for two people and a supply temperature of 43°C (109°F) during summer operation of the heating system. However, brine is used.
Hello,
The buffer tank is not for domestic hot water but is part of a closed circuit. As I understand it, the fresh water station is a heat exchanger that then extracts heat from this buffer. The advantage is supposed to be that there are fewer issues with Legionella at lower temperatures.
Best regards
Christian
The buffer tank is not for domestic hot water but is part of a closed circuit. As I understand it, the fresh water station is a heat exchanger that then extracts heat from this buffer. The advantage is supposed to be that there are fewer issues with Legionella at lower temperatures.
Best regards
Christian
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