I am currently in the process of renovating our souterrain basement, starting with my future “mancave”. As opposed to the rest of the house, the basement is not insulated at all, with external walls 36 cm of concrete bricks and an uninsulated foundation (20 cm concrete slab according to the original building documents).
I will add 5 cm of insulation to the external walls, as well as 1 cm below the flooring I plan to put in. Nevertheless, the required heating power will be strongly decoupled from the external temperature, as most of the walls are either to an adjacent unheated storage room external to the house or to internal unheated basement rooms. Furthermore I suspect heat loss to the floor is more significant that through the walls. I recently measured required heating power in this room with an electrical heater, and while I needed 750 W at 0°C outdoor temperature, this only dropped to around 550-600 W at almost 10°C. I suspect this varies more seasonally than with daily temperature swings as ground temperature changes.
My problem is integrating this thermal behaviour with the rest of my quite well insulated house. Pure weather compensation keeps temperatures around 21°C in the house from -10°C (32°C flow) to 10°C (26 °C flow).
I basically need a solution that can work within these constraints, as I don’t want to increase flow temperatures. The rest of the house has type 33/22 radiators with fans, but I don’t think I can reach the output modulation I need just by varying fan speeds. I need more or less constant heat output despite varying flow temperatures. A further complication is the dT, which is of course bounded by the room temperature, so at 10°C outdoor temperature I only have a max delta of 6K to work with when targeting 20°C indoor. What other options do I have? Fan coils? Special heat pump radiators? The existing type 22 radiator in this basement room gets me to a maximum of 17°C with 10 fans at full blast; and I can’t tolerate that kind of noise.
I could of course add infrared geating elements, but my heatpump has so much headroom in power that it feels like a complete waste to not utilize it as much as possible.
To make a long story short - how do I get between 500 and 1000 W of heat out of very low flow temperatures; more or less decoupled from the actual flow temperature?
I would like to directly connect the emitter to my existing manifold in the basement, which allows individual pipe flow rate settings. I could vary flow rate there, but are there systems that allow a true quantitative electronic control of flow rate?
Maybe a smart trv that you could either use as is? If you have a big enough radiator the trv will just maintain the room temperature, it’s not like your whole heating system will be messed up by it.
Or a smart trv controlled by something like HA if that’s your thing, ie you understand it
I do have smart TRVs but in my experience the window of actual flow rate control beyond on-off is very limited. But that’s actually a good idea; if there were any really quantitative systems that would be even better.
My heat pump is always running, there are no off-times during the heating season. I would like to have the basement as a continuous extra load as this will allow my heat pump to finally operate in its modulating region. Currently, it is very much oversized and always cycles. Having this extra heat loss in the basement is just enough to allow continuous operation when <°C. So an on-off control will be bad as I need continuous heat pump load.
My Daikin is twice as big as I need but never cycles.
What I do have is something akin to your basement, a conservatory that has a wildly different heat loss to the rest of the house, just like your basement.
But i am not too concerned about it’s temperature so just live with what I get.
In your case, if you fitted a trv in the basement, whilst the basement needed heat it would help reduce the cycling.
Once the base is warm enough to close the trv and remove the load, you are no worse off than you are now.
Look at it this way, if the heat demand of your basement is zero because it is warm enough and the heat pump cycles, there is no difference to how it is now, you cannot manufacture a heat demand that does not exist.
This is true, but only in a time-averaged manner. A TRV - if only operating in a binary on/off fashion will overshoot temperature, close down flow and then wait until a hysteresis is reached to activate flow again. This cycling will interact with the heatpump controls and the heatpump might just match the heating cycle of the TRV. On a not-so-terribly-oversized system like mine, this will not matter but I’d really like to get to a continuous operation regime as it also increases comfort in the house - no more temperature oscillations with cycling.
Fit a massive K3 rad or two in there, with a load of 140mm fans underneath, and call it a day.
Or the money-gun option might be routing channels in the concrete floor for embedding UFH pipes, with zero insulation underneath, and using the entire slab (and some of the earth underneath) as a giant thermal store.
I heated for a week straight. It took more than three days to equilibrate. That’s also how I saw that there is barely any dependence on outdoor temperature.
I’m expecting a 100-200 W reduction from the external wall insulation. The floor insulation is mostly for comfort. I’m having real issues getting a good estimate as only 20% of the heat loss is towards exernal walls. I’ve got no real clue how to accurately estimate heat loss into the ground.
I have a similar setup, souterrain basement whose heating load is decoupled from outdoor temperature/rest of the house. Its never been a problem for me; the basement temperature can change noticeably, but its not a lot.
Its very much self-regulating: low-temp rads put out significantly less heat as the room temp rises, and unless your basement is hermetically sealed off from the rest of the house, the warmer air will rise.
So, when outside temps suddenly drop, it gets pleasantly warm down there, which is perfect on a cold day, until equilibrium is reached and its back to normal.
The opposite happens when a warm-front comes through, basement temps drop a bit. I rather be outside on a nice day than in the basement anyway… but even here, as room temp drops, the rads will put out more heat as dT increases, so the room temp doesn’t actually fall that much, especially if rads are oversized (mine aren’t), then I imagine it would be even less an issue.
I have TRVs on the rads in the basement, but leave them fully open 100% of the time. Its never gotten so warm that I needed them.
Its most noticeable in the spring when air temps rise quickly but the ground stays frozen for a while.
My temperature swings are also bigger than yours probably:
Climate: -24C design temp,
Basement walls: ~65% below-grade, ~35% exposed to outside air,
Basement rads: slightly under-sized,
Insulation: ~2cm rigid foam underfoot, ~5cm rigid foam + ~10cm mineral wool batts on the walls.
An oversized rad with TRV is the way to go, in my opinion. Keep it simple, let it self-regulate.
I have two thoughts. When I learned to be a solar installer we were taught that the best value was to put money into conserving energy as opposed to generating more energy. I think the same is true here; more insulation.
My other thought is on a dehumidifier. You don’t want things to get wet. Which spawns a third thought. Consider heat recovery ventilation (HRV) This technology makes the inside like outside but warm and, when done right, significantly reduces energy costs. My experience was in a 150 sq M well insulated house which was heated with a wood stove using one 1/2m x 15cm round log a day.
Your basement almost describes my whole house before modification. Solid 230mm brick walls and a solid concrete floor in the kitchen. The wall insulation is sheets of 50mm PIR stood up against the wall and held in place with roofing laths screwed to the wall every 400 mm, The laths are 20mm thick so with a sheet of 12mm plasterboard on top you have a very well insulated decoration ready wall with a useful 20mm gap into which you can route the wiring for your man cave. (thanks to building control for this tip). Tape the joins between the boards to get continuous seal on the foil facing and you get a vapour barrier as well.Floors done with waterproof 20mm marmox boards which are load bearing once tiled and can be tiled on easily. Laminate flooring would work also.Heat recovery ventilation works wonders, is ace at keeping any condensation issues at bay, you no longer need noisy ventilation fans in bathrooms and you can seal up trickle vents. (note if you have open fires or gas appliances you will need expert advice, otherwise its a DIY possible job.The only downside is that it is so good at distributing air around the house that the whole house tends to end up at the same temperature. It should assist with your radiator balancing issue, as any excess heat in the man cave will just get moved elsewhere.
Passive house model uses a U=2.0 for solid floors, so wall to soil conduction will be similar. I like Nigel’s 20mm solid flooring insulation for the thermal comfort aspect, cold feet being unpleasant. You might consider insulation to the unheated rooms too because the wall and air in there will be in good thermal equilibrium with the soil
