Air to water heat pump
redbird2010
4 years ago
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sktn77a
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Need recommendations for air sourced cold climate heat pumps
Comments (29)Re: Symie “Can any one of you answer the question of how to install a HP without the need for backup or fossil fuels? That was the original question.” I see you’ve already made your choice, that’s great. As you have already chosen a gas system, I’ll try to give you the short answer. An Air-Source Air-to-Liquid HP utilizing Variable Speed Compressor technology (VRF) & Enhanced Vapour Injection (EVI), that you already indicated that you know something about, is the choice of HP able to operate at very low Outdoor Temperatures averaging a ‘Seasonal’ COP fairly close to that of geothermal - without the need of a ground loop (geothermal is still the Gold Standard - but at a price). The indoor distribution is via hot or chilled water feeding in-floor radiant, heat emitters (radiators) fan coils units to change indoor temperatures quickly (heating or cooling), hydronically fed central fan coil units (to condition an entire floor), chilled beams or any combination there of. The way the Defrost Mode can work without backup is that in heating mode, the only mode requiring Defrost, is that a hydronic system employs the use of a buffer tank that stores hot water. The buffer tank can have many functions besides the prevention of short cycling (as when one small zone such as a bathroom in-floor radiant zone or even just a hydronically heated towel warming rack calls for heat), depending on design of the system. It can be configured that during Defrost Mode, the thermal energy stored in the Hot Water Buffer Tank is diverted and used to defrost the HP condenser coil while simultaneously continuing to heat the home, as there is enough stored thermal energy to do both. Depending on the design of the buffer tank system there might be as much as a 5˚F -10˚F drop in temperature of the stored hot water - but that temporary drop in water temperature would hardly be felt in the home because unlike a ‘Conventional’ Air-Source HP that completely switches over to Air-Conditioning, the Hydronic system might see that drop in buffer tank stored water from possibly 120˚F to say, 110˚F - not enough to feel any real difference in the home for perhaps the 20-minutes it takes to defrost and even less so with a system designed with all emitters operating at a design water temperature of 110˚F. Afterwards, the buffer tank quickly recovers when the HP fully switches back to heating. Keep in mind that when doing things the ‘Conventional’ way you still have at least 2-separate systems, such as a gas furnace and an air-conditioner. The system described above can be 1-fully integrated system for space heating, air-conditioning, Domestic Hot Water production - all with 1-source of energy, 1-utility entrance and 1-bill. It can also be designed to perform all functions all at the same time. “Current HVAC has 88K BTU and can't keep up as we get down toward single digits and 3 ton cooling which struggles to keep up over 90 degrees.“ Given your situation, I personally would be looking to do something quite different. While you should be able to sort out your HVAC challenges with conventional forced air technology, I would be concerned that some issues while ameliorated were not quite resolved leaving me unhappy. I might therefore choose water knowing that if I could deliver the right temperature water to all distribution points within the envelope, an easy task with proper design, that I could with the right emitters and fan coils, control the temperature in all parts of the home - heating and air-conditioning. Keeping to a specific temperature, water is easier to control than airflow. A modern water ECM circulator (pump) might drawing 50-watts (small incandescent light bulb) for the whole house instead of a ½-HP Blower Motor. Hydronics are much easier to zone and control than forced air. A 1-inch insulated pipe might be easier to install than duct work. "A given volume of water can absorb almost 3500 times a much heat as the same volume of air, when both undergo the same temperature change.” 3/4"tube = 20"x12" duct 3/4"tube = 18" ø duct Having said all this, I would still insist on an electric boiler backup in case of a real Emergency, such as a Compressor Lockout Condition or if for any reason the HP could not keep up with the envelope or DHW heat loss, if that were part of the design - but not for reasons of Defrost! While I’m not on-site to first hand evaluate your situation, if this were my home, I would look to do something cutting edge and radially different, rather than ducted forced air that has given you no real satisfaction. Please keep in mind - I am NOT trying to sell you anything. A HP Hydronic conversion would be a much more expensive Premium solution! ‘Think Water’ (But don't drown in the details) IMPO SR...See MoreDaikin heatpump crazy high stand-by power consumption
Comments (15)Re: David Cary “Wouldn't a "crankcase heater" be thermostatically controlled so not likely to be continuous. It would seem to be an incredibly lazy design if that were not the case.” So far I have been unsuccessful in locating Carrier schematics that include crankcase heaters, although I’m not investing much time to do so. I know that our geothermal HP does have one and remember calling and questioning the president and chief design engineer (about 20-years ago) about not only its inclusion in the design but that in particular it being a waste of energy because it is not temperature controlled (always ‘ON’) and that in most geothermal designs it’s just not needed in that the compressor in a geothermal HP is located inside the conditioned space of the building envelope. He agreed and remarked that in all his years of being in business no one had ever challenged the legitimacy of the design, he was not complaining, just suggesting no one had drilled that deeply into the schematic. My background is in electronics long before ever getting involved professionally in geothermal was what I told him. In fairness, I would speculate that these off the self compressors used in this design all included crankcase heaters because the manufacturer could not predict where or in what application they might be used and separate production runs (with & without heaters) would not be cost effective. Our geothermal HP is an R-22 reciprocating compressor design. Subsequent models of the same series with r410a Scroll compressors, no longer indicate any crankcase heaters. Back to your question. I would imaging that temperature control of any crankcase heater would be a logical requirement, if needed at all, for Energy Star accreditation. That seems to me to be a no-brainer, as well as controls that require a current draw below 5-watts and perhaps below even 1-watt in ‘stand-by’ mode for Energy Star certification. However things are probably further complicated by systems having to power remote illuminated T-Stats and blower fans that might always be ‘ON’ even at a minimum flow rate to circulate the air, humidify the air in heating mode and filter the air year round for better IAQ. IMPO SR...See Morereplace steam boiler or convert to hot water/forced air?
Comments (8)You need to make sure that whichever HVAC contractor you choose does a legitimate (ie, not fudged) heat load calculation. It's a calculation that considers a number of factors specific to the size of the home, its rooms, and its construction and not the least of which being where your home is located, to determine how much heat needs to be produced to keep the home comfortable when it's cold outside. Rule of thumb and rough approximation were used in the past and rounded up with the result that other than homes built by conscientious tradespeople like in the last 10 years, most homes have waaay larger heating and cooling equipment than they need. More isn't better, oversized equipment produces less comfort at greater cost than when the right sizes are determined and installed. Again, good luck....See MoreHas anyone done 'staple up' for air to water radiant heat pump system?
Comments (23)Remember that you can use any hydronic technique like Warm Board for under floor radiant tubing method. You don‘t have to do in-slab if you don’t want to. Nordic air-to-water is another option if you don’t want to do geothermal. The advantage of any Nordic air source heat pump is that there is less equipment outside. That contributes to a longer life cycle and it is ‘local’ for you. I believe the federal government will contribute $5k for geothermal so that covers a lot of the drilling cost. You might also choose a geothermal triple function HP with forced air heating & cooling AND full capacity hot water for radiant heat and DHW production if your budget permits. You didn’t mention any details of your new home as to sizes or floors or your electrical rate. BTW: We have a Nordic geothermal heat pump (Montreal) for almost 20 years. Hasn’t failed yet and I don’t know anyone with a similar size house that heats for le$$! IMPO SR...See MoreMatt McLagan
4 years agonexp
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4 years agoSpringtime Builders
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