ᐅ 3x buffer tanks – number of heat exchangers and domestic hot water connections?
Created on: 28 Mar 2024 16:38
J
JanseppHello,
I have the following question and hope to get some advice:
I want to connect a Viessmann Verticell 340M (750L) with two buffer tanks.
The Verticell has a solar heat exchanger. For this, there are 6 panels available with a total area of about 12 m² (130 sq ft).
Additionally, the storage tank contains an internal stainless steel coil to heat 40 liters (11 gallons) of domestic hot water.
I have two questions:
1. The 40 liters (11 gallons) of domestic hot water seem insufficient for a household of 5 people. Should I connect an additional domestic hot water storage tank of about 150 to 300 liters (40 to 80 gallons)? So that the water in the coil (inside the large buffer tank) is heated and then collected in the smaller domestic hot water tank?
2. Do the other two buffer tanks also need to have a heat exchanger? I assume they do not, but is there a limitation of the heat exchanger in the Viessmann unit that prevents it from using the full power from all solar thermal panels?
Thank you very much and best regards
I have the following question and hope to get some advice:
I want to connect a Viessmann Verticell 340M (750L) with two buffer tanks.
The Verticell has a solar heat exchanger. For this, there are 6 panels available with a total area of about 12 m² (130 sq ft).
Additionally, the storage tank contains an internal stainless steel coil to heat 40 liters (11 gallons) of domestic hot water.
I have two questions:
1. The 40 liters (11 gallons) of domestic hot water seem insufficient for a household of 5 people. Should I connect an additional domestic hot water storage tank of about 150 to 300 liters (40 to 80 gallons)? So that the water in the coil (inside the large buffer tank) is heated and then collected in the smaller domestic hot water tank?
2. Do the other two buffer tanks also need to have a heat exchanger? I assume they do not, but is there a limitation of the heat exchanger in the Viessmann unit that prevents it from using the full power from all solar thermal panels?
Thank you very much and best regards
The proposed setup seems rather unusual at first glance; providing more background information would likely result in more responses.
In principle, domestic hot water is produced in a buffer tank with a stainless steel coil in a flow-through system. The 40L (11 gallons) likely refers only to the capacity of the stainless steel coil. However, the hot water output cannot be directly derived from this figure. Relevant parameters include the total volume of the buffer tank (750L (198 gallons)) and the system temperature of the heating water during winter without solar input.
The efficiency of the solar thermal system is influenced by how the three planned buffer tanks are connected. Why install three buffer tanks instead of one larger one? What is the purpose of having three? Is the goal to store solar input over a longer period, essentially to manage through a cloudy day in spring without using the heating system? If so, the buffer tanks need to be sized quite large.
In principle, domestic hot water is produced in a buffer tank with a stainless steel coil in a flow-through system. The 40L (11 gallons) likely refers only to the capacity of the stainless steel coil. However, the hot water output cannot be directly derived from this figure. Relevant parameters include the total volume of the buffer tank (750L (198 gallons)) and the system temperature of the heating water during winter without solar input.
The efficiency of the solar thermal system is influenced by how the three planned buffer tanks are connected. Why install three buffer tanks instead of one larger one? What is the purpose of having three? Is the goal to store solar input over a longer period, essentially to manage through a cloudy day in spring without using the heating system? If so, the buffer tanks need to be sized quite large.
Hello, since wood is the primary energy source, our house requires about 2100 liters (550 gallons). Due to the available ceiling height, it is not possible to install one or two very large tanks, so it needs to be divided into three tanks, each with a capacity of 750 liters (200 gallons).
Thanks for the additional information. For wood heating, the system temperature in the buffer tank with a stratified tank configuration will likely be around 65 degrees Celsius (149°F), so from my perspective, this provides sufficient domestic hot water capacity for 5 people. I would definitely avoid adding an extra domestic hot water storage tank. You should choose either one or the other, or a third option: a fresh water station via a heat exchanger.
The three buffer tanks can be connected in series or parallel. One possible setup could be as follows: only one buffer tank has a solar heat exchanger while the two additional buffers are connected in parallel. Parallel means connecting the heating water volumes of all three buffers at as many different stratification levels as possible. The more connections there are, the better and faster the temperature levels can equalize across the different buffers. An optimal temperature stratification is desirable. Further explanations on this topic can be found, for example, online under "Bosy cascade connection series connection."
Apparently, the Vitocell 750 buffer tank has only 4 connections at different heights in total – a few more would be better. Ideally, the two additional buffers would have the same connections at the same height levels. This point concerns me somewhat, and I would look for a buffer tank with more connection points. In the worst case, the additional buffers might only "partially" participate. Therefore, I might prefer a tank in a special design with just 1500 liters (400 gallons) rather than 2250 liters (600 gallons) split over three buffers. If all three buffers receive a solar heat exchanger, this would increase the solar yield and lead to more uniform stratification. Of course, this would also cost a bit more.
The three buffer tanks can be connected in series or parallel. One possible setup could be as follows: only one buffer tank has a solar heat exchanger while the two additional buffers are connected in parallel. Parallel means connecting the heating water volumes of all three buffers at as many different stratification levels as possible. The more connections there are, the better and faster the temperature levels can equalize across the different buffers. An optimal temperature stratification is desirable. Further explanations on this topic can be found, for example, online under "Bosy cascade connection series connection."
Apparently, the Vitocell 750 buffer tank has only 4 connections at different heights in total – a few more would be better. Ideally, the two additional buffers would have the same connections at the same height levels. This point concerns me somewhat, and I would look for a buffer tank with more connection points. In the worst case, the additional buffers might only "partially" participate. Therefore, I might prefer a tank in a special design with just 1500 liters (400 gallons) rather than 2250 liters (600 gallons) split over three buffers. If all three buffers receive a solar heat exchanger, this would increase the solar yield and lead to more uniform stratification. Of course, this would also cost a bit more.
Jansepp schrieb:
Thank you for your reply. So ideally, I should have 3 identical storage tanks, as this would mean all connections are at the same height and I would have a total of 3 solar heat exchangers. Is that correct?Yes, that's correct. This way, the temperature conditions in all 3 buffer tanks will be as equal as possible.
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