ᐅ Underfloor Heating and Air-to-Water Heat Pump in New Construction: Am I Inviting Problems?
Created on: 16 Jul 2021 18:03
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neo-sciliar
Hello everyone,
I have posted here several times before and have received a lot of really helpful advice. I have learned a lot. But reality is catching up with me: we are currently building a new house, and because of the builder, we are tied to a specific heating installer (alternatively, we could choose our own, but then we would have to find all the other tradespeople ourselves, including electrical, plumbing, and everything that follows). Since this is already contractually agreed, the matter is settled.
In my opinion, based on what I have learned here, he is doing everything "wrong":
1.) Viessmann air-to-water heat pump Vitocal 222-S with 7.2 kW, although the calculation shows only 5.5 kW needed
2.) Buffer tank to enable flow rate and prevent short cycling
3.) ERRs (electronic room regulators) in the main rooms (he wanted ERRs in all rooms, I limited it to the important ones)
4.) I saw on site today: heating circuits of varying lengths—from 30 m (98 feet) up to 120 m (394 feet). At least the spacing of the underfloor heating pipes is adjusted according to the room requirements, from 5 cm (2 inches) in the bathroom to 30 cm (12 inches) in the bedroom
Now my questions: Am I setting myself up for real problems, or is all this actually irrelevant (as he claims) and the system will still run properly? By properly I mean that a) it heats well and b) electricity consumption stays within reasonable limits (seasonal performance factor > 4.5, calculated at 4.9).
Best regards, Andreas
I have posted here several times before and have received a lot of really helpful advice. I have learned a lot. But reality is catching up with me: we are currently building a new house, and because of the builder, we are tied to a specific heating installer (alternatively, we could choose our own, but then we would have to find all the other tradespeople ourselves, including electrical, plumbing, and everything that follows). Since this is already contractually agreed, the matter is settled.
In my opinion, based on what I have learned here, he is doing everything "wrong":
1.) Viessmann air-to-water heat pump Vitocal 222-S with 7.2 kW, although the calculation shows only 5.5 kW needed
2.) Buffer tank to enable flow rate and prevent short cycling
3.) ERRs (electronic room regulators) in the main rooms (he wanted ERRs in all rooms, I limited it to the important ones)
4.) I saw on site today: heating circuits of varying lengths—from 30 m (98 feet) up to 120 m (394 feet). At least the spacing of the underfloor heating pipes is adjusted according to the room requirements, from 5 cm (2 inches) in the bathroom to 30 cm (12 inches) in the bedroom
Now my questions: Am I setting myself up for real problems, or is all this actually irrelevant (as he claims) and the system will still run properly? By properly I mean that a) it heats well and b) electricity consumption stays within reasonable limits (seasonal performance factor > 4.5, calculated at 4.9).
Best regards, Andreas
J
JansEigenheim16 Jul 2021 23:16What design temperatures were used for calculating the underfloor heating? It should be around 35-30°C (95-86°F) supply temperature. It would be better to have something closer to 30-29°C (86-84°F) with NAT.
A lot of correct points have already been made here. However, it is unlikely to be efficient. The annual performance factor seems overly optimistic; a more realistic value is around 3 with air source and proper design.
Specifically, the different lengths should be recalculated to achieve uniform circuit lengths (is there a room-by-room heating list available?). Whether NO (normally open) or NC (normally closed) thermostats are used doesn’t matter much if you disconnect or unscrew them. NO thermostats are less common and significantly more expensive based on what I’ve found so far. Additionally, I don’t think it’s smart to only have the main rooms controllable, because this means that rooms meant to stay cooler, like utility rooms, will be heated as long as the pump is running.
There are also quick schematics available for heat pumps without a buffer tank, if I’m not mistaken.
Specifically, the different lengths should be recalculated to achieve uniform circuit lengths (is there a room-by-room heating list available?). Whether NO (normally open) or NC (normally closed) thermostats are used doesn’t matter much if you disconnect or unscrew them. NO thermostats are less common and significantly more expensive based on what I’ve found so far. Additionally, I don’t think it’s smart to only have the main rooms controllable, because this means that rooms meant to stay cooler, like utility rooms, will be heated as long as the pump is running.
There are also quick schematics available for heat pumps without a buffer tank, if I’m not mistaken.
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nordanney17 Jul 2021 07:40borxx schrieb:
It probably won’t be very efficient. The annual performance factor also seems overly optimistic; realistically, about 3 can be expected with air-source and proper design. Could you please explain why?
borxx schrieb:
I would specifically have the different lengths recalculated to have a uniform length of the loops (room-by-room heating layout, correct?). A uniform length throughout is a frequently repeated mantra—around 100m (330 ft). That’s also accurate for the site. However, as always, it’s more of an ideal to achieve 110% efficiency.
But it’s absolutely not a problem if, for example, some short loops are used for the corridor and/or guest bathroom. That doesn’t matter at all. And even longer loops are not a big deal with today’s heat pumps, since basically every heat pump can provide sufficient flow rate. Even for 120m (390 ft) loops, which can occur due to the floor plan.
neo-sciliar schrieb:
The spacing of the underfloor heating pipes is adapted to the demand in the room, from 5cm (2 inches) in the bathroom up to 30cm (12 inches) in the bedroom. What kind of demand do you have in the bedroom if 30cm (12 inches) spacing is sufficient? Or, conversely, what is the supply temperature to actually get any heat into that room?
Otherwise, it seems someone has at least put some thought into it, even if the implementation is not 100% perfect (see buffer tank).
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neo-sciliar17 Jul 2021 08:32The heating load was calculated per room based on 35/30. In the bedroom, we basically don’t need any heating.
Again: I have no influence over the heating technician. He is beyond any arguments, and the general contractor trusts him. If it were up to me, we would already have switched from Viessmann to a Nibe or AiT. Without a buffer in the supply line.
Again: I have no influence over the heating technician. He is beyond any arguments, and the general contractor trusts him. If it were up to me, we would already have switched from Viessmann to a Nibe or AiT. Without a buffer in the supply line.
Regarding the annual performance factor, there is a heat pump consumption database (for those who want to look it up) where many members of a certain pink forum diligently enter their data. That would be my basis for the statement that values of 4.5 or even almost 5 are very optimistic; in recent years, the average has been around 3.4, often with systems that are probably more optimized than what is planned here. My concern is about expectations and why the heating engineer will likely never guarantee a factor of 4.5.
Yes, the pumps are capable of that. On the other hand, from a cost/benefit perspective, in my opinion, it is one of the most sensible measures. Every additional heating circuit adds material costs (manifold, thermostat, switching actuator...) and, in the long term, more electricity consumption for pumps. Even if it only saves a few watts continuously, that easily leads to a pretty decent hourly wage for about 2 extra hours of planning effort.
Don’t worry if you can’t change anything anyway. In the end, it might just mean 10 or 20€ more per month for heating, which probably won’t be noticeable in the overall context.
Yes, the pumps are capable of that. On the other hand, from a cost/benefit perspective, in my opinion, it is one of the most sensible measures. Every additional heating circuit adds material costs (manifold, thermostat, switching actuator...) and, in the long term, more electricity consumption for pumps. Even if it only saves a few watts continuously, that easily leads to a pretty decent hourly wage for about 2 extra hours of planning effort.
Don’t worry if you can’t change anything anyway. In the end, it might just mean 10 or 20€ more per month for heating, which probably won’t be noticeable in the overall context.
Of course, circuits that are too short are not good. With return-controlled heat pumps, thermal short-circuiting occurs at the latest, causing the heat pump to shut off even though the rooms with longer circuits still require heating.
Design it properly—ONCE. Then continuously gain efficiency afterward.
It doesn’t matter what the heating installer says. YOU are paying, and the construction will be done according to YOUR requirements. Once they’ve got their money through the general contractor, they’re gone and you’ll be left chasing after them.
Request a room-by-room heating load calculation, then have the underfloor heating designed with similarly sized heating circuits, NO buffer tank, and use wall heating instead of a ladder-type radiator in the bathroom.
Design it properly—ONCE. Then continuously gain efficiency afterward.
It doesn’t matter what the heating installer says. YOU are paying, and the construction will be done according to YOUR requirements. Once they’ve got their money through the general contractor, they’re gone and you’ll be left chasing after them.
Request a room-by-room heating load calculation, then have the underfloor heating designed with similarly sized heating circuits, NO buffer tank, and use wall heating instead of a ladder-type radiator in the bathroom.
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