Meurastein1 May 2014 10:42Hello,
We are about to start building a single-family house on short notice. For the heating system, we have chosen a ground source heat pump with deep boreholes.
However, we are quite uncertain about the type of heat pump and its capacity.
The house will be 143 m² (1540 ft²), with underfloor heating, insulation around the KfW 70 standard, a family of five, and a 200-liter (53 gallons) buffer tank.
The offers we have received range from 5.9 kW to 7.7 kW (Viessmann Vitocal 222) up to 8 kW. The required heat pump capacity calculated by the companies ranges from around 5 kW to 7 kW.
We often hear and read that the correct sizing of the heat pump is key to low heating and hot water costs. Due to the many different recommendations and calculations, we are now quite confused.
Who can help? What capacity should the heat pump have?
Is 5.9 kW sufficient? Would 7.7 kW be better?
Or should it be something else entirely?
We are about to start building a single-family house on short notice. For the heating system, we have chosen a ground source heat pump with deep boreholes.
However, we are quite uncertain about the type of heat pump and its capacity.
The house will be 143 m² (1540 ft²), with underfloor heating, insulation around the KfW 70 standard, a family of five, and a 200-liter (53 gallons) buffer tank.
The offers we have received range from 5.9 kW to 7.7 kW (Viessmann Vitocal 222) up to 8 kW. The required heat pump capacity calculated by the companies ranges from around 5 kW to 7 kW.
We often hear and read that the correct sizing of the heat pump is key to low heating and hot water costs. Due to the many different recommendations and calculations, we are now quite confused.
Who can help? What capacity should the heat pump have?
Is 5.9 kW sufficient? Would 7.7 kW be better?
Or should it be something else entirely?
Masipulami1 May 2014 10:45I can't really say much about the heat pump at the moment, but a 200-liter (53-gallon) buffer tank seems a bit small for five people.
T
toxicmolotof1 May 2014 10:56What is the buffer tank used for? Domestic hot water or heating?
Meurastein1 May 2014 10:57The buffer tank is for the heating system. The hot water storage tank has a capacity of 170 liters (45 gallons).
Hello,
In addition, for sizing the source (ground heat), you need to know how many kWh per year it must supply in total. It is also important to know the peak cooling load.
Otherwise, it remains guesswork, estimating, or assumptions. For that, the investment would be too high for me.
Best regards
Meurastein schrieb:Sometimes a more affordable trench collector can also be sufficient.
..... We decided on a ground source heat pump with deep drilling as our heating system....
Meurastein schrieb:Usually everyone calculates with their own, mostly sales-driven, physics. ;-)
....The offers range from 5.9 kW to 7.7 kW (Viessmann Vitocal 222) up to 8 kW. The heating capacity calculated by the companies for the heat pump ranges from 5.x to 7.x kW…..
Meurastein schrieb:Correct! For precise sizing, the actual demand (capacity, energy) for heating and hot water must first be calculated (basic assessment). The room heating loads also need to be known in order to design the heating surfaces and hydraulics properly.
....We often hear and read that the correct sizing of the heat pump is the key to low heating and hot water costs.…
In addition, for sizing the source (ground heat), you need to know how many kWh per year it must supply in total. It is also important to know the peak cooling load.
Meurastein schrieb:An independent MEP planner with appropriate professional experience.
....Who can help?
Otherwise, it remains guesswork, estimating, or assumptions. For that, the investment would be too high for me.
Best regards
170 liters (45 gallons) of hot water for 5 people is definitely far too small. At least 300 liters (80 gallons) is needed.
The buffer tank for the heating system is technically not necessary and can actually be counterproductive for consumption. However, a heating system without a buffer tank is quite difficult to adjust and balance properly if you want to avoid any loss of comfort. The heating installer can’t manage this because it would require living with you for a year. Therefore, heating installers generally tend to equip systems with a buffer tank by default.
The size of the heat pump should ideally be calculated by the house manufacturer or the architect. After all, a heating load calculation is done for this purpose.
I can only provide a rough comparison:
For my 225 square meters (2,420 square feet) of gross floor area (= 174 square meters (1,872 square feet) of living space plus gallery and other space) and a KFW70 standard from the builder, 6.7 kW was calculated. As a safety margin, I added a bit and installed 7.8 kW. That was a small mistake. 6.7 kW would have been correct. However, we are only two people. In comparison, I would assume that for your case, the lower value is the more appropriate choice.
If the heat pump is somewhat oversized, it can be compensated fairly well with various settings. That’s not a disaster. Much more important is that the pipes of the underfloor heating are spaced closely, around 10 cm (4 inches). Builders often try to save money here.
The buffer tank for the heating system is technically not necessary and can actually be counterproductive for consumption. However, a heating system without a buffer tank is quite difficult to adjust and balance properly if you want to avoid any loss of comfort. The heating installer can’t manage this because it would require living with you for a year. Therefore, heating installers generally tend to equip systems with a buffer tank by default.
The size of the heat pump should ideally be calculated by the house manufacturer or the architect. After all, a heating load calculation is done for this purpose.
I can only provide a rough comparison:
For my 225 square meters (2,420 square feet) of gross floor area (= 174 square meters (1,872 square feet) of living space plus gallery and other space) and a KFW70 standard from the builder, 6.7 kW was calculated. As a safety margin, I added a bit and installed 7.8 kW. That was a small mistake. 6.7 kW would have been correct. However, we are only two people. In comparison, I would assume that for your case, the lower value is the more appropriate choice.
If the heat pump is somewhat oversized, it can be compensated fairly well with various settings. That’s not a disaster. Much more important is that the pipes of the underfloor heating are spaced closely, around 10 cm (4 inches). Builders often try to save money here.
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