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Old 29.01.2021, 23:34
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Urgent Help on heat pump (air-water) selection

Dear all,

I have shortlisted 2 quotations for heat pump with under-floor heating installation from 2 different installers for the house we are to move-in in 3 months, however as I have very little experience/knowledge of technicalities with heat pumps, I am not able to compare which one is better of the two. Its a big investment (at least for me), therefore wanted to be abs sure.

One is Mitsubishi and another is Stiebel Eltron from 2 different installers - both well known brands, perhaps Stiebel Eltron is known to be better and slightly more expensive than Mitsubishi from hearsay. (I also hear, although may be wrong, that Mitsubishi is "not in the list of approved manufacturers" - whatever that means!!)

Someone who has good technical knowledge of heat pumps, can shed some light? I am happy to share the quotes which has the details if you have some knowledge and can give some useful insights.

Pompe chaleur air | eau STIEBEL ELTRON WPL
Puissance calorifique A-7/W35: 6,86 kW
Pompe chaleur air/eau Mitsubishi New Silent Power Inverter puissance de 3,4 kw 9,3 kw avec compresseur classe A++
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Old 30.01.2021, 01:08
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Re: Urgent Help on heat pump (air-water) selection

6kw? What are you heating? Your porch or greenhouse?

Are you sure theyve sized it right?
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Old 30.01.2021, 11:46
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Re: Urgent Help on heat pump (air-water) selection

It's tool long to write here.
- what are projected losses per day at -7C ?
- what is average termp in region you live ?
- sunshine ?
- other sources of energy ( bi-walent ?).
- how many hours of operation per day were calculated at peek -7C ?
- how big is the buffer (if any) ?
- heating water for how many people ?
- how many total hours of operation per year ?
- inverter or on-off pump ?
- what COP/JAZ ?
- Pump must be Swiss certified for subsidiary $$$ from canton.
- Split or monoblock ?
- E-heating size below target temperatures ?
- are noise requirements meet ?

pump usualy is about 1/2 to 1/4 of total expenses .

Right installation company should have these answers for you right away for above questions and explain what is important to look at.

Example of "bad"advise is
- here is a pump and based on your current usage it would do in a season based on let's say current oil usage :
1400L oil a seasons
120days of heating seasons

1400L/120d => 12L/day -> that is 120Kwt so 6.6KW pump would do in 19h ...

issue is - that it's averaged across 120days - while not covering peak energy needs for two months where usage is 2-3x that of rest of the heating season and likely for 2-months you'd end up using electro heating which is 3-4x more expensive than heatpump.

so above example calculation (depends on region) would be 1400L/120*1.7
that would mean about 10KW pump would cover between 95%-100% of the heat demand on the season.

Keep in mind that most installation companies make money not on heatpump but on work they do on all the other components so "cheaper" pump is a tactic to win the customer and make profit elsewhere - while you left with an issue on your own ( it's not their fault how their sized heat-demand - it be you to judge).

You may also think about m2 of the property as simple measure
Construction year :
..check in internet
1990-2000 -> 50W/m2
2000-2010.-> 25W/m2

My one is 1999 with 35W/m2 as example.

hope that helps

Last edited by hoover1; 30.01.2021 at 14:46. Reason: add on
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