ᐅ Replacement of Oil Heating System with Heat Pump, Underfloor Heating, and Wood Boiler
Created on: 2 Jun 2022 13:21
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Ebedi22
Hello, we are planning to renovate the basement of our house. Current situation:
The energy consultant’s renovation plan includes the following initial steps:
Further insulation measures are planned in later phases of the renovation, but these are currently postponed because they are too complex and therefore too expensive. Additionally, I am considering installing a controlled mechanical ventilation system (for indoor climate and humidity) as a DIY project, as well as adding a wood heating system for winter (possibly a wood gasifier or replacing the old inefficient fireplace in the living room with something more efficient). We practically have access to firewood for free (just need to cut and bring it in).
I have already gathered useful information on this topic here in the forum, but I still have some questions:
Thank you very much for your patience in reading this and for any answers!
- Two-story house (living area approx. 243m² (2,613 sq ft), built in 1977) with flat roof (roof was renewed and insulated a few years ago)
- Underfloor heating on the ground floor (from the beginning), radiators in the basement
- The basement is partially built into a slope; so far only one room is actively used as an office and heated during the week, the rest is unheated
- Heating and hot water production are oil-based (annual consumption approx. 2000 liters (530 gallons) per year; the energy consultant independently calculated a final energy consumption of 39,500 kWh/year and a primary energy demand of 191 kWh/(m²a) (61,720,000 BTU/(ft²a)))
- Almost all windows on the ground floor have been gradually replaced over recent years
The energy consultant’s renovation plan includes the following initial steps:
- Insulation of the basement exterior walls including new windows (possibly internal insulation on the wall facing the slope)
- Insulation of the basement floor and replacement of radiators with underfloor heating
- Replacement of the oil heating system with an air-to-water heat pump
- According to the energy consultant, this will result in a specific primary energy demand of 49 kWh/(m²a) (15,790,000 BTU/(ft²a)) and an expected final energy consumption of 9,700 kWh/year
Further insulation measures are planned in later phases of the renovation, but these are currently postponed because they are too complex and therefore too expensive. Additionally, I am considering installing a controlled mechanical ventilation system (for indoor climate and humidity) as a DIY project, as well as adding a wood heating system for winter (possibly a wood gasifier or replacing the old inefficient fireplace in the living room with something more efficient). We practically have access to firewood for free (just need to cut and bring it in).
I have already gathered useful information on this topic here in the forum, but I still have some questions:
- I often read that a heat pump combined with underfloor heating is best operated without a storage tank. The reasons seem plausible to me, but I wonder how this is actually implemented. My heating installers’ quotes all include a storage tank (probably required by each heat pump manufacturer). Since I’m not a professional and don’t want to disregard manufacturer specifications (in case of problems or warranty issues, I would be responsible), my question is: Are there heat pump manufacturers that do not require a storage tank? Or more generally, how do proponents of “no storage tank” operate their systems at home?
- One installer generously offered an 18 kW heat pump, another suggested 12 kW. Considering the current oil consumption of 2000 liters, should not something around 8 kW be sufficient, especially combined with the wood heating?
- The “old” underfloor heating on the ground floor has relatively wide pipe spacing (you can feel warm and cold spots). The new underfloor heating in the basement will of course have closer pipe spacing (better heat transfer → lower supply temperatures). The heated floor areas are roughly the same size. Could this cause issues, for example with pressure, flow rates, or the old underfloor heating unnecessarily raising the supply temperature? If yes, what would be suitable measures?
- Until the children are old enough to move to the basement, only the office there will need heating for the next few years. From an energy-saving perspective, is it sensible and feasible to hydraulically/thermally balance the heating system so that the basement (possibly excluding the office) remains cooler, and then carry out a new balancing once the children move downstairs (which could coincide with future energy measures on the ground floor)?
- Is there any risk to the heat pump if the old underfloor heating is connected directly (corrosion, materials no longer used today, etc.)?
- The bathroom on the ground floor has underfloor heating but is not warm enough when the children bathe. So far, we manage by turning on the towel radiator in advance, which is connected to the high-temperature heating circuit in the basement. However, that will be eliminated. Could the towel radiator be connected to the hot water cylinder instead (properly sized, possibly a combi boiler, since we plan to install a fresh water station or similar for domestic hot water anyway)? Is this reasonable or even allowed? This would have the advantage that the heat pump could run more efficiently for normal heating and only provide a short-term higher temperature level for the occasional children’s bath. If not, any other ideas?
- Which type of (log wood) heating system would be recommended in this case? A wood gasifier in the basement or a new stove in the living room? As I see it:
- Advantages of a wood gasifier: heat can be used for heating the whole house or for domestic hot water, possibly eligible for subsidies
- Advantages of a living room stove: cheaper upfront cost, works during power outages, offers the “coziness factor”
- Disadvantage of the living room stove: heat is only locally available and cannot be used for (less efficient) domestic hot water production combined with the heat pump — is it realistic to expect any noticeable (electricity) savings in winter, or would that be offset by still needing the heat pump for the rest of the house and the hot water, with only the living room being warmer?
Thank you very much for your patience in reading this and for any answers!
D
Deliverer2 Jul 2022 08:49It’s simple: Traditional air-to-air heat pumps (“air conditioners”) are almost always oversized. There’s no way around it because they hardly come below 2 kW. Even in an unrenovated older building, only a very large living room typically requires 2 kW of heating or cooling capacity.
Regarding heating and cooling loads: theoretically, they are the same. But only if the temperature difference were equal. In Germany, for example, the temperature difference between indoors and outdoors in winter is about 30°C (54°F), while in summer it’s around 15°C (27°F). So technically, cooling systems could be sized smaller, but such options simply aren’t available.
By the way, your assumption is correct: multiple single-split units are cheaper, more efficient, and more redundant than one multi-split system. The only downside is having more outdoor units.
If you plan to use the system for heating, make sure the units can operate down to -15°C (5°F) or even -20°C (-4°F). Manufacturers often offer special “arctic” versions for this purpose. Additionally, floor-mounted units are quieter when heating because they release warm air at floor level instead of having to blow it downward. However, they tend to have drawbacks in cooling comfort.
Regarding heating and cooling loads: theoretically, they are the same. But only if the temperature difference were equal. In Germany, for example, the temperature difference between indoors and outdoors in winter is about 30°C (54°F), while in summer it’s around 15°C (27°F). So technically, cooling systems could be sized smaller, but such options simply aren’t available.
By the way, your assumption is correct: multiple single-split units are cheaper, more efficient, and more redundant than one multi-split system. The only downside is having more outdoor units.
If you plan to use the system for heating, make sure the units can operate down to -15°C (5°F) or even -20°C (-4°F). Manufacturers often offer special “arctic” versions for this purpose. Additionally, floor-mounted units are quieter when heating because they release warm air at floor level instead of having to blow it downward. However, they tend to have drawbacks in cooling comfort.
So, the plumber has now said that the old underfloor heating system (upstairs) cannot be connected directly to the heat pump, as there is a risk of damaging the pump. If I understood correctly, it would need to be connected via a heat exchanger. I don’t find that ideal, because there will be some temperature loss along the way, but since I don’t want to risk damaging the heat pump, I’m willing to accept that... I can manage a lower supply temperature upstairs anyway, since there are other heating options and solar gains available.
The question that concerns me more is: what does this mean for the rest of the system? Would it still be possible to connect the new underfloor heating (basement) and the heat exchanger directly to the heat pump without a buffer tank (or at most a small one on the return side) and operate at least this part efficiently? Or are there hydraulic or other reasons against this (I have no idea how a heat exchanger would affect the overall system)?
The question that concerns me more is: what does this mean for the rest of the system? Would it still be possible to connect the new underfloor heating (basement) and the heat exchanger directly to the heat pump without a buffer tank (or at most a small one on the return side) and operate at least this part efficiently? Or are there hydraulic or other reasons against this (I have no idea how a heat exchanger would affect the overall system)?
What exactly did he state as the reason? It is quite possible that there could be issues without additional measures. However, from my layperson’s perspective, this would likely lead to problems with efficiency and possibly the minimum flow rate.
I am also aware of the option to install microbubble separators and a sludge separator, specifically on the return line to protect the heat pump. Whether this is sufficient, I cannot judge and would probably clarify that in a forum specialized in building services engineering.
I am also aware of the option to install microbubble separators and a sludge separator, specifically on the return line to protect the heat pump. Whether this is sufficient, I cannot judge and would probably clarify that in a forum specialized in building services engineering.
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SaniererNRW12321 Aug 2022 12:55Joedreck schrieb:
What exactly was the reason he gave? It is quite possible that there could be problems without additional measures. In my layman’s view, this would likely cause issues with efficiency and possibly the minimum flow rate.
I am also aware of the option to install microbubble separators and a sludge separator, specifically on the return line, to protect the heat pump. I cannot assess whether this is sufficient and would probably discuss this in a forum specialized in building services engineering. It couldn’t have been explained better. The heating technician’s explanation is unsatisfactory because it lacks justification.
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