ᐅ Is an air-to-water heat pump a practical option for renovating a listed building to meet Efficiency House standards (160% energy savings regulation)?
Created on: 14 Jan 2021 09:11
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RomeoZwo
Hello everyone,
This is about the renovation of a listed single-family house for rental purposes. According to the energy consultant (an architect specializing in renovations), using an air-to-water heat pump is recommended because a gas condensing boiler would require significantly more insulation work (internal insulation of 8cm (3 inches) instead of 4cm (1.5 inches)) and thus reduce the living space. The air-to-water heat pump could be installed in the basement, with air intake and exhaust through the former coal window (basement top edge about 80cm (31 inches) above ground level). Photovoltaic or solar thermal systems are not possible due to heritage protection. Until now, I had assumed a gas boiler for the house since there is a gas connection in the street, although it has not yet been connected to the house (original heating was a central coal heating system, but unused and unoccupied for 30 years).
As a rental property, it is also interesting that the green/red political plans to impose the CO2 tax on landlords would not be problematic in this case, since electricity costs are charged directly to the tenant and therefore initially would not appear in the additional costs.
On paper, the air-to-water heat pump is clearly advantageous, but what is the reality here? In 2017, we chose gas for a new build due to the high electricity consumption. This is an old building that is allowed to have up to 60% more primary energy demand than a new build. Can the figures for the air-to-water heat pump be trusted to some extent, or will the electricity consumption be a disaster?
Thanks in advance for your opinions—I had never really considered an air-to-water heat pump before and therefore haven't looked into it much yet.
This is about the renovation of a listed single-family house for rental purposes. According to the energy consultant (an architect specializing in renovations), using an air-to-water heat pump is recommended because a gas condensing boiler would require significantly more insulation work (internal insulation of 8cm (3 inches) instead of 4cm (1.5 inches)) and thus reduce the living space. The air-to-water heat pump could be installed in the basement, with air intake and exhaust through the former coal window (basement top edge about 80cm (31 inches) above ground level). Photovoltaic or solar thermal systems are not possible due to heritage protection. Until now, I had assumed a gas boiler for the house since there is a gas connection in the street, although it has not yet been connected to the house (original heating was a central coal heating system, but unused and unoccupied for 30 years).
As a rental property, it is also interesting that the green/red political plans to impose the CO2 tax on landlords would not be problematic in this case, since electricity costs are charged directly to the tenant and therefore initially would not appear in the additional costs.
On paper, the air-to-water heat pump is clearly advantageous, but what is the reality here? In 2017, we chose gas for a new build due to the high electricity consumption. This is an old building that is allowed to have up to 60% more primary energy demand than a new build. Can the figures for the air-to-water heat pump be trusted to some extent, or will the electricity consumption be a disaster?
Thanks in advance for your opinions—I had never really considered an air-to-water heat pump before and therefore haven't looked into it much yet.
N
nordanney14 Jan 2021 10:09Air-to-water heat pumps are calculated to be suitable for the KfW program – at the targeted efficiency level, however, the tenant is likely to be pleased...
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Daniel-Sp14 Jan 2021 10:27Here are the following questions.
1. What is the heating load?
2. What type of heat distribution system is planned? Underfloor heating or radiators?
3. What supply temperature is targeted?
Without knowing this, I would generally expect a high heating load, with radiators and a high supply temperature. This would argue against an air-to-water heat pump.
In rental situations, I would prefer gas over a heat pump, as it is less problematic. Alternatively, if storage space is available, pellets could also be an option.
1. What is the heating load?
2. What type of heat distribution system is planned? Underfloor heating or radiators?
3. What supply temperature is targeted?
Without knowing this, I would generally expect a high heating load, with radiators and a high supply temperature. This would argue against an air-to-water heat pump.
In rental situations, I would prefer gas over a heat pump, as it is less problematic. Alternatively, if storage space is available, pellets could also be an option.
N
nordanney14 Jan 2021 10:32Daniel-Sp schrieb:
1. What is the heating load.It depends on whether eight or four cm (3 or 1.5 inches) of insulation are installed. The heating load is higher with an air-to-water heat pump than with gas. The results from KfW calculations are absurd.Hello,
The planned heat distribution system is underfloor heating, which operates at relatively low supply temperatures. The house is about 120m² (1290 sq ft).
To just meet the requirements of the energy-efficient monument standard, the following applies:
with gas and 8cm (3 inches) of insulation (thermal conductivity 042) on the inside:
Primary energy (per m² of usable floor area): 117.43 kWh/(m²·a)
Transmission heat loss Ht`: 0.468 W/(m²·K)
with an air-to-water heat pump and 4cm (1.5 inches) of insulation (thermal conductivity 042) on the inside:
Primary energy (per m² of usable floor area): 85.72 kWh/(m²·a)
Transmission heat loss Ht`: 0.537 W/(m²·K)
What kind of energy (electricity) costs are we talking about for the air-to-water heat pump at temperatures around 0°C (32°F)? Is it about 10€ per day or per week? Besides the fact that the tenant pays for the electricity, I am already concerned about the debate regarding the landlord's share of the CO2 tax. Thanks to subsidies, the investment costs for a high-quality, internally installed air-to-water heat pump would be lower than for a gas condensing boiler (since the insulation material thickness is also reduced by 50%). An additional benefit is that the rentable floor space remains larger. Of course, I do not want frequent tenant turnover due to high electricity costs, but if the difference is about ±50€ per month between gas and air-to-water heat pump, I think that is acceptable for a tenant. How would the use (not the calculation) of an additional wood stove affect this? The chimney is already there and would no longer be needed with the air-to-water heat pump.
The planned heat distribution system is underfloor heating, which operates at relatively low supply temperatures. The house is about 120m² (1290 sq ft).
To just meet the requirements of the energy-efficient monument standard, the following applies:
with gas and 8cm (3 inches) of insulation (thermal conductivity 042) on the inside:
Primary energy (per m² of usable floor area): 117.43 kWh/(m²·a)
Transmission heat loss Ht`: 0.468 W/(m²·K)
with an air-to-water heat pump and 4cm (1.5 inches) of insulation (thermal conductivity 042) on the inside:
Primary energy (per m² of usable floor area): 85.72 kWh/(m²·a)
Transmission heat loss Ht`: 0.537 W/(m²·K)
What kind of energy (electricity) costs are we talking about for the air-to-water heat pump at temperatures around 0°C (32°F)? Is it about 10€ per day or per week? Besides the fact that the tenant pays for the electricity, I am already concerned about the debate regarding the landlord's share of the CO2 tax. Thanks to subsidies, the investment costs for a high-quality, internally installed air-to-water heat pump would be lower than for a gas condensing boiler (since the insulation material thickness is also reduced by 50%). An additional benefit is that the rentable floor space remains larger. Of course, I do not want frequent tenant turnover due to high electricity costs, but if the difference is about ±50€ per month between gas and air-to-water heat pump, I think that is acceptable for a tenant. How would the use (not the calculation) of an additional wood stove affect this? The chimney is already there and would no longer be needed with the air-to-water heat pump.
D
Daniel-Sp14 Jan 2021 14:32The primary energy per square meter from the KfW calculation doesn’t help much initially to estimate the heating load. If you have Ht and the building volume, you can at least make an estimate. Try searching for Trenchplaner and ring trench collector.
The first consideration is what supply temperature you can realistically achieve with the underfloor heating. For this, you need a room-by-room heat load calculation to properly size the underfloor heating for each room. Then, you can see which supply temperature is required. Only after that can you decide whether an air-to-water heat pump makes sense or is just a money pit.
Another point is whether the KfW ERR is required. If yes, the heating installer will either install a separation buffer or a bypass valve to ensure the minimum flow rate for the heat pump. Since you are renting out, you have no control over whether the ERR is used by the tenants or not. This means you won’t be able to close the bypass valve. An open bypass valve or separation buffer leads to a cycling heat pump, which means higher wear and premature failure. This also eliminates the cost advantage over gas heating. An even bigger problem is a combination storage tank, as this can cause issues with the domestic hot water supply.
I personally have an air-to-water heat pump and am very satisfied. However, I have spent a lot of time on the design of the underfloor heating and the technology and operation of the heat pump. That’s why I would never choose a heat pump for a rental property. It has too many pitfalls and demands discipline and knowledge from the operator/tenant. Therefore, the question arises whether a pellet heating system might still be an option, or otherwise gas.
The first consideration is what supply temperature you can realistically achieve with the underfloor heating. For this, you need a room-by-room heat load calculation to properly size the underfloor heating for each room. Then, you can see which supply temperature is required. Only after that can you decide whether an air-to-water heat pump makes sense or is just a money pit.
Another point is whether the KfW ERR is required. If yes, the heating installer will either install a separation buffer or a bypass valve to ensure the minimum flow rate for the heat pump. Since you are renting out, you have no control over whether the ERR is used by the tenants or not. This means you won’t be able to close the bypass valve. An open bypass valve or separation buffer leads to a cycling heat pump, which means higher wear and premature failure. This also eliminates the cost advantage over gas heating. An even bigger problem is a combination storage tank, as this can cause issues with the domestic hot water supply.
I personally have an air-to-water heat pump and am very satisfied. However, I have spent a lot of time on the design of the underfloor heating and the technology and operation of the heat pump. That’s why I would never choose a heat pump for a rental property. It has too many pitfalls and demands discipline and knowledge from the operator/tenant. Therefore, the question arises whether a pellet heating system might still be an option, or otherwise gas.
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