Dear heat pump experts and experienced home builders,
I would like to better understand what heat pump capacity we actually need.
Our project:
2 full floors
No basement
148 sqm (1,593 sq ft)
KFW55 standard
In our energy demand calculation, a 6 kW air-to-water heat pump is recommended.
However, the heating load calculation in the plan specifies an 8 kW air-to-air heat pump.
Both calculations seem to follow a standard procedure, as this is a developer project.
Which figures in both documents should I focus on?
To me, 8 kW seems quite high, but this is just a feeling formed by reading here in the forum.
The underfloor heating is already installed, also standard, and the screed has been curing for 4 weeks, waiting for the system to be heated up.
But there is no heat pump installed yet.
The builder would credit us €15,000 if we handle the purchase and installation of the heat pump ourselves.
All these questions are overwhelming us.
Is this even possible? Can we choose a different model or manufacturer?
Is it worthwhile, is €15,000 a reasonable amount?
Is 6 kW enough? ...
We need solid information to stand our ground with the builder.
Help!
Thanks!
I would like to better understand what heat pump capacity we actually need.
Our project:
2 full floors
No basement
148 sqm (1,593 sq ft)
KFW55 standard
In our energy demand calculation, a 6 kW air-to-water heat pump is recommended.
However, the heating load calculation in the plan specifies an 8 kW air-to-air heat pump.
Both calculations seem to follow a standard procedure, as this is a developer project.
Which figures in both documents should I focus on?
To me, 8 kW seems quite high, but this is just a feeling formed by reading here in the forum.
The underfloor heating is already installed, also standard, and the screed has been curing for 4 weeks, waiting for the system to be heated up.
But there is no heat pump installed yet.
The builder would credit us €15,000 if we handle the purchase and installation of the heat pump ourselves.
All these questions are overwhelming us.
Is this even possible? Can we choose a different model or manufacturer?
Is it worthwhile, is €15,000 a reasonable amount?
Is 6 kW enough? ...
We need solid information to stand our ground with the builder.
Help!
Thanks!
S
SaniererNRW12317 Nov 2022 15:50junijulibaut schrieb:
Thanks for the tip about the planning tool.
I entered the data. It looks like it results in a 6 kW system (blue line), but the 8 kW system is close as well. Screenshots attached. You can also calculate your heating load using a different tool. Try searching Google for "trench collector heat pump consumption database energy saving regulation heating load." It is very close to the detailed calculation (from a group of DIY enthusiasts).
J
junijulibaut17 Nov 2022 15:56I will try that too, just for fun, but it doesn’t really help us. Thank you.
D
driver55a17 Nov 2022 20:43@junijulibaut: Thanks for the pictures. The heating coils are laid out quite sparsely in some places. 🙄
The heating load is only one part of the equation. That means, what demand the building has (including hot water), and how that energy is supplied are two different issues.
Simply put, if you only have 20 meters (65 feet) of underfloor heating in a room, logically you need to run at a higher temperature than if you had 40 meters (131 feet) or even 60 meters (197 feet). Key point: flow velocity.
And the 6.2 kW rating doesn’t even include hot water demand.
I would rather go for the "bigger" heat pump.
The heating load is only one part of the equation. That means, what demand the building has (including hot water), and how that energy is supplied are two different issues.
Simply put, if you only have 20 meters (65 feet) of underfloor heating in a room, logically you need to run at a higher temperature than if you had 40 meters (131 feet) or even 60 meters (197 feet). Key point: flow velocity.
And the 6.2 kW rating doesn’t even include hot water demand.
I would rather go for the "bigger" heat pump.
J
junijulibaut17 Nov 2022 20:58Thanks for the assessment.
It also matches my impression—everything is just pretty standard.
If our estimate of 8kW isn’t too far off, that’s good.
We’ll pay for the very straightforward pipe spacing with a higher supply temperature and thus higher electricity costs. But that will be the next chapter once the heat pump is installed and running.
It also matches my impression—everything is just pretty standard.
If our estimate of 8kW isn’t too far off, that’s good.
We’ll pay for the very straightforward pipe spacing with a higher supply temperature and thus higher electricity costs. But that will be the next chapter once the heat pump is installed and running.
S
SaniererNRW12317 Nov 2022 21:16driver55a schrieb:
For example, if there are only 20 m (65.6 ft) of underfloor heating in a room, logically a higher temperature has to be set than with 40 m (131.2 ft) or even 60 m (196.8 ft). However, this has nothing to do with the heating load, as you yourself mention. Whether an oversized 8 kW heat pump runs the supply temperature at 35 degrees Celsius (95°F) or the appropriate 5 or 6 kW heat pump does it, makes no difference. Both can handle it—one just more efficiently than the other (the larger one).
And always keep in mind that the heating load is calculated for -15 degrees Celsius (5°F) or whatever temperature is used. These cold days are, if at all, very rarely reached. Therefore, the actual heating load during a normal winter is significantly lower than the calculated value. That’s why it’s perfectly fine to choose a smaller heat pump. In the end, it doesn’t matter for the original poster since they will get the 8 kW unit anyway.
D
driver55a17 Nov 2022 21:19junijulibaut schrieb:
higher flow temperature and thus higher electricity costs Speaking of electricity costs:
Today I received the future heat pump tariffs from the local utility. 😳
Peak rate: 36.17 cents/kWh previously 23.52 cents/kWh --> 53.8% more expensive
Off-peak rate: 30.20 cents/kWh previously 17.65 cents/kWh --> 71.7% more expensive
Basic fee: from €108 per year to €114 per year
And this already includes the loyalty discount of 13% for 13 years.
In 2009, the off-peak rate was around 9.x cents/kWh.
Annual consumption: 2500 kWh–3000 kWh.
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