Heating a House with Two Heat Sources - Page 1
Forum section: electronics / general

author: Alti
author_rank: Frequent Contributor
timestamp: March 17, 2020, 07:41:57 pm
content: What do you think about a concept of a modern house heated by two heat sources:primarily by a low power and highly efficient electric heat pump (time lag inevitable)complemented by relatively high power electric infrared emitters (super fast)?So when you are out, everything is turned off (0W) but when you want to enter the room, infrared preheats the room in seconds and then the heat pump takes over.The goal is to reduce the energy consumption as no energy is consumed when room/house is empty*. Occupation depends on circumstances (office, church etc.) but lets focus on a house and assume a typical working family.

author: james_s
author_rank: Super Contributor
timestamp: March 17, 2020, 07:50:40 pm
content: At least in the USA where forced air heat is the norm, heat pumps already typically have electric resistance supplemental heat and any kind of forced air heat tends to warm the place up pretty quickly. Don't forget another significant aspect though, heating all the objects in the room. You could heat the air very quickly but if the sofa you sit on and the furniture and objects around you are cold you'll still feel cold. Also many people have pets so it's important to think of them too, you don't want the dog or cat to be cold while you're out of the house. I have my heat dial back several degrees at night and when nobody is home but I don't want it to ever get below about 60F.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 17, 2020, 08:23:18 pm
content: To keep the overall energy need low one should have good insulation. With good insulation the temperature will not drop very fast. So at least for a normal home with would be more constant temperature anyway. Also if the insulation at the outside is much better than between the rooms, one would end up with little difference between the rooms. Gradient between rooms can be a problem anyway, as the could rooms will concentrate the humidity. If this is a problem depends on the area and general humidity level.Compared to a heat pump IR is relatively low efficiency (e.g. 1/3 ... 1/6 of the heat pump). It may help for a short time - but only short time, to avoid peak power from the heat pump. This would be more like the cases the control did not work as expected.

author: Alti
author_rank: Frequent Contributor
timestamp: March 17, 2020, 09:33:23 pm
content: Quote from: james_s on March 17, 2020, 07:50:40 pmOk, thanks, this looks to me like the same concept but with different lag.Well, I meant more like seconds, not minutes.It is a tradeoff between heat consumption and comfort. The shorter this lag is, the more you can save energy (theory).Quote from: Kleinstein on March 17, 2020, 08:23:18 pmWell, what about if the insulation at the outside is same as in between the rooms? The idea is not to tweak an existing house but to create a design that saves energy by not using it when the room is not occupied. Of course if the house has all rooms 100% occupied 24/7 then this is a mute concept.As for comment on good insulation - I must say that if the room is 50% unoccupied with half of the regular insulation then it will consume same energy as the one that is 100% occupied, regular insulation. Under assumption the ramp up and ramp down with the temperature is insignificantly short and does not cost and does not create other problems (is comfortable).So, it is not the "good insulation" but "good product of insulation*occupancy" that matters in above concept.BTW, how much time do you spend in bedroom per 24h? If it is like most of us then either you need the third of the insulation or you are wasting 2/3 of the energy.

author: Ccandrews
author_rank: Contributor
timestamp: March 19, 2020, 06:48:01 am
content: When we built our house we made a few excellent decisions regarding the HVACWe put in a geothermal heat pump that uses a huge underground liquid loop for its outside reservoir. Summer or winter the temperature of that loops stays about the same so the efficiency of our system is fairly constant.we used hydronic heating in our floors and each room is its own zone. Cold bedrooms, warm bathrooms, comfortable living areaswe have a de-superheat heat exchanger on the heat pump so in the summer the reject heat goes into our domestic hot water pre heat tankswe use the geothermal heat pump to take the domestic hot water up to about 115 degreesF and from there electric to the final temperaturewe insulated all the interior wallswe put in a heat recovery ventilator that transfers nearly all the heat from the exhaust air into the incoming fresh airThe one thing I missed when designing the system is that I should have entirely encompassed the septic tank with the geothermal loop since that is where the bulk of the energy is wasted via hot water down the drain whose energy could have been recovered.For decades it bugged me that my wife will run the heat in the morning and the air conditioning in the afternoon. Now I just smile and know that when she flips on the AC she is just making the hot water for my next shower. It has surely added years to my life.

author: mzzj
author_rank: Super Contributor
timestamp: March 19, 2020, 08:50:00 pm
content: I'm assuming that you are from country without real winter.1. 0W is not enough to keep the house from freezing if you have any sort of winter at all. OK you could keep the house on "standby" with 500...1000W.2. fast heating leaves all surfaces cold to touch and generally uncomfortable feel for 1-2hours. If your normal room temperature is +23c you could lower the standby setting to something like +18c3. AFAIK in many countries electric company charges you extra if you put large peak load on system.cutting the ventilation off when there is no occupancy and indoor CO2+moisture levels are enough low could be one way to do it. Ventilation uses suprising amount of heating energy.

author: Alti
author_rank: Frequent Contributor
timestamp: March 22, 2020, 08:39:48 pm
content: Quote from: Ccandrews on March 19, 2020, 06:48:01 amOk, thank you for the input. That means you most likey have a heat source with inertia counted in minutes. Can you ramp up (air) temperature in a room by 5degK in 5 seconds? If not then you have to keep +-constant temperature in zones during whole heating season. Maybe modulating those zones day/night with slow ramp up and down. But the trick described in opening post won't work with only heat pump, it is too slow.Quote from: mzzj on March 19, 2020, 08:50:00 pmCentral EU, -15degC happens sometimes. My question is a generic one. I do not ask for a solution for a specific house or location but more about the concept of two sources thatcomplementeach other in a domain of: power installed, time response, efficiency and installation cost.Heat pump / IR1kW / 50kW500s / 5sCOP~5 / COP~110k€ / 1k€Regarding 3 questions:1: Cars work this way - you do not leave the engine idling in winter when you are at groceries. But I get it, there are limits to this 0W concept to avoid condensation, thermal stress, freezing your flowers, etc.2: That is another challenge. I think this "comfort perception" is a function of the specific heat of the walls, thermal conductivity, construction etc. If that is a rock castle it may not get comfortable till spring but if the walls are made out low thermal conductivity material, may we talk about seconds under 50kW beam?3: My energy provider does not. 50kW for 10 seconds costs same as 5kW for 100 seconds.

author: SolarMan
author_rank: Contributor
timestamp: March 30, 2020, 04:08:54 pm
content: I think that the very best solution would be to turn the heat pump on about an hour before the family is due to arrive home (using an automatic timer/mobile app).Where timers/remote control is not available, I think your solution makes a lot of sense, especially in poorly insulated houses where the cost of running the heat pump all day could be very high.On the other hand, heat pumps are generally recommended only for homes that have decent insulation to begin with (at least this is the official advice in Ireland, seehttps://www.seai.ie/publications/Homeowners-Guide-To-Heat-Pump-Systems.pdf). Of the two people I know with heat pumps here, both only run the heat pumps at night (cheaper night rate power). Their homes are well enough insulated to retain the heat throughout the day.