ᐅ Cooling via underfloor heating with a ground-source heat pump
Created on: 30 Apr 2015 11:27
S
SirSydom
Hello everyone,
I am very sensitive to heat, so this will be a major focus in our new build.
In addition to an automatic shading system with venetian blinds and roller shutters, and a solid construction method, as well as a ventilation system with a bypass (and possibly a ground heat exchanger), I am considering whether "passive" or "free" cooling through the underfloor heating system makes sense. This is said to have only low operating costs since only electricity for the pumps is required. The technology also seems quite simple—a heat exchanger between the brine circuit and the underfloor heating circuit, possibly with a few valves and a mixer.
Now I am wondering if the effort is worthwhile—does it really make a difference? Does anyone have a direct comparison in the same house, once with and once without?
My wife is still quite hesitant because she fears having cold feet. "In summer, I want to walk barefoot." Is this concern justified?
Are there alternatives for cooling that won’t immediately break the budget? A separate cooling ceiling would certainly cost several thousand euros.
With a conventional split air conditioning unit, I can already hear my wife complaining about drafts, so that option is probably off the table.
I am very sensitive to heat, so this will be a major focus in our new build.
In addition to an automatic shading system with venetian blinds and roller shutters, and a solid construction method, as well as a ventilation system with a bypass (and possibly a ground heat exchanger), I am considering whether "passive" or "free" cooling through the underfloor heating system makes sense. This is said to have only low operating costs since only electricity for the pumps is required. The technology also seems quite simple—a heat exchanger between the brine circuit and the underfloor heating circuit, possibly with a few valves and a mixer.
Now I am wondering if the effort is worthwhile—does it really make a difference? Does anyone have a direct comparison in the same house, once with and once without?
My wife is still quite hesitant because she fears having cold feet. "In summer, I want to walk barefoot." Is this concern justified?
Are there alternatives for cooling that won’t immediately break the budget? A separate cooling ceiling would certainly cost several thousand euros.
With a conventional split air conditioning unit, I can already hear my wife complaining about drafts, so that option is probably off the table.
Mycraft schrieb:
The cost for the pump is roughly about 10€ per month, which is just a drop in the ocean in every respect.
The cooling capacity of a heated floor system is around 20-30 W/m² (1.9–2.8 W/ft²). To effectively cool an average house, you need approximately 100 W/m² (9.3 W/ft²). Electricity Consumption
My electricity consumption for passive cooling is less than 40 watts. It runs on average about 12 hours a day. At my current electricity price of 27 cents/kWh, that amounts to less than 4€ per month. In practice, as another user mentioned, cooling is mostly done during periods of surplus photovoltaic power, so it costs me only the feed-in tariff of around 11 cents/kWh, which means under 2 euros per month for electricity... for me that is practically "free" to operate.
Cooling Capacity
Our system delivers somewhere around 2–2.5 kW (which roughly matches your lower estimate of 20 W/m² if I exclude the areas that are not cooled). This cooling power is absolutely sufficient, with proper shading, to maintain the house at a consistently low temperature even during extended heat waves. Of course, it doesn’t cool quickly from 29°C (84°F) down to 20°C (68°F), but that is not part of our house concept. Energy efficiency and sustainability were high priorities; I do not want an air conditioner, but I do want a cool home in summer if possible (not 19°C (66°F) with 35°C (95°F) outdoors, but comfortably cool for living and sleeping).
Unfortunately, I don’t have thermally activated concrete slabs, which I regret a bit in hindsight, as that would have made the whole system even more efficient.
@Dew Point "Issue": I have a sensor monitoring the dew point. I have not had any problems so far in summer. The supply temperature is adjusted accordingly; even in the very rare cases where the supply temperature must be limited to a maximum of 19–20°C (66–68°F), the cooling capacity remains sufficient (although the pump electricity consumption may increase by about 20 watts due to the higher flow rate needed because of the smaller temperature difference). There is a good thread on this topic in the purple forum with statistics, I am not allowed to link it here, but anyone can google it.
annab377 schrieb:
hhmm. And the people who notice a scratchy throat without an enthalpy exchanger, because the air is too dry, usually only experience this in winter, when the outdoor air is also rather dry?Yes, only in winter and mostly when temperatures are around 0°C (32°F) ±5° and below. At higher temperatures, the relative humidity is generally more comfortable.
Of course, there are exceptions, and some people simply find it too dry at all times.
Tego12 schrieb:
@Dew Point "Issue": I have a sensor that monitors the dew point. I haven’t had any problems with it in the summer so far. The supply temperature is simply adjusted accordingly.Where is the sensor installed? Inside the heat pump itself? Which temperatures does it use for the dew point calculation? The temperatures of the individual rooms?
annab377 schrieb:
Where is the sensor installed? Inside the heat pump itself? Which temperatures does it use for the dew point calculation? The temperatures of the individual rooms? We have a central sensor in the living area (the warmest and most humid part of our house, since about 90% of our daily life takes place there). The sensor is integrated into the control unit of the heat pump (we have a Stiebel Eltron WPL 05 cool). I checked the values with a local measuring device; apart from a minor deviation, everything is within the expected range. The system applies a safety margin anyway, so that puts you on the very safe side.
Oh, and the cooling effect is easiest to notice when away on holiday:
The house naturally warms up slowly when unoccupied, despite shading. If I switch on the passive cooling about 2–3 days before we return, the temperature drops by several degrees (the cooling power is of course a bit higher than during normal operation because the house is warmed up, so the temperature difference is greater).
Okay, good. So you’re basically recommending not only cooling through the underfloor heating pipes but also accepting the effort and costs (possibly a thicker concrete slab due to structural requirements and pipes plus additional equipment for the circuit) of the chilled beam system to make it even more efficient?
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