Log in
Register
Home
Forums
New posts
Search forums
What's new
New posts
New profile posts
Latest activity
News
Members
Current visitors
New profile posts
Search profile posts
Features
Log in
Register
Search
Search titles only
By:
Search titles only
By:
New posts
Search forums
Menu
Install the app
Install
Reply to thread
Home
Forums
Off Topic
The Basement
Home building/living suggestions wanted.
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Message
<blockquote data-quote="Ryan Lantzy" data-source="post: 73354" data-attributes="member: 7"><p>Re: Home building/living suggestions wanted.</p><p></p><p></p><p></p><p>Typically you have three options for a ground sourced heat pump. Slinky coil beds in a pond of sufficient depth, slinky coil beds buried under the frost line, or "wells" for lack of a better word. Usually each 100 feet length of slinky coils provides 1 ton of cooling or heating. One vertical well is typically the same. There needs to be good contact between the coils or well elements and the earth for them to remain efficient. (Pond based systems are pretty easy to get high efficiency out of because the water provides 100% slinky coil surface coverage.)</p><p></p><p>Pretty much anyone can get this to work on any size of land, though wells cost a little more (figure $1500-$2000 per well). Slinky coils are cheaper, and if you can operate a backhoe and call your state utility commission to get get gas lines, electrical lines, etc. marked, it's pretty simple. Wells require much more specialized equipment.</p><p></p><p>Air source units really don't "stop working" below a certain temperature. The coefficient of performance (COP) declines as the the temperature differential goes up. Eventually it gets to a point where its just as effective as resistance heating (1:1). The maximum theoretical COP is calculated based on temperature differential, but currently the most efficient systems top out between 4 to 4.5:1. Most currently installed systems are between 2.5 and 3.5:1. Cycle time greatly affects efficiency which is why an oversized system can be so detrimental to your energy use. Not only does it take more input to drive a bigger compressor, the unit doesn't hit max efficiency until the cycle is in full swing. Once it gets there, it heats the air up fast, and shuts off. This is typically referred to as "short cycling." If the unit is large enough, and puts out enough BTU at this point, you still may not need resistance heating - but you probably aren't saving much money either. You can do a load estimation on your house and determine how many BTUs/hr your house loses on the coldest day and design for that. Although, for the sake of efficiency, I've read designing for worst case is not ideal. Basically, on the 95th percentile days you want your heat pump running almost all day long, just keeping up with losses. Then on the coldest days, you turn on an auxiliary heat source to get you through (heat strips, a fire place, whatever).</p><p></p><p>The systems can (and do) freeze up frequently, but this is why they have a defrost cycle. The defrost cycle for the outdoor part just runs the refrigerant cycle in reverse (A/C mode), stealing a little heat away from your house. Usually the fan shuts off during this part so you don't get blasted with cold air, but it depends on the system. What you DON'T want is your indoor coil freezing up because most systems don't have defrost sensors or defrost cycles for the indoor coils. However, frozen coils are almost always caused by three things: a grossly over sized A/C unit, an undersized air handler and/or ducting, or a very dirty filter. You can also freeze them up by setting the indoor temp too low.</p><p></p><p></p><p></p><p></p><p>Time based control is one of the things that new Nest thermostat relies on. It has sensors to monitor activity in the home (people passing by, etc.) and smarts to measure the lag of the HVAC system and time of day changes from solar input. Then it adjusts the heating/cooling cycle to make sure the house is comfortable when you are there and livable but probably not comfortable when you are not.</p><p></p><p></p><p></p><p>It is for this reason specifically that I oppose government incentives on wind and solar at this point rather than spending it on basic research. The efficiency is just not there yet, but may be if we put more time into research and making some breakthroughs.</p></blockquote><p></p>
[QUOTE="Ryan Lantzy, post: 73354, member: 7"] Re: Home building/living suggestions wanted. Typically you have three options for a ground sourced heat pump. Slinky coil beds in a pond of sufficient depth, slinky coil beds buried under the frost line, or "wells" for lack of a better word. Usually each 100 feet length of slinky coils provides 1 ton of cooling or heating. One vertical well is typically the same. There needs to be good contact between the coils or well elements and the earth for them to remain efficient. (Pond based systems are pretty easy to get high efficiency out of because the water provides 100% slinky coil surface coverage.) Pretty much anyone can get this to work on any size of land, though wells cost a little more (figure $1500-$2000 per well). Slinky coils are cheaper, and if you can operate a backhoe and call your state utility commission to get get gas lines, electrical lines, etc. marked, it's pretty simple. Wells require much more specialized equipment. Air source units really don't "stop working" below a certain temperature. The coefficient of performance (COP) declines as the the temperature differential goes up. Eventually it gets to a point where its just as effective as resistance heating (1:1). The maximum theoretical COP is calculated based on temperature differential, but currently the most efficient systems top out between 4 to 4.5:1. Most currently installed systems are between 2.5 and 3.5:1. Cycle time greatly affects efficiency which is why an oversized system can be so detrimental to your energy use. Not only does it take more input to drive a bigger compressor, the unit doesn't hit max efficiency until the cycle is in full swing. Once it gets there, it heats the air up fast, and shuts off. This is typically referred to as "short cycling." If the unit is large enough, and puts out enough BTU at this point, you still may not need resistance heating - but you probably aren't saving much money either. You can do a load estimation on your house and determine how many BTUs/hr your house loses on the coldest day and design for that. Although, for the sake of efficiency, I've read designing for worst case is not ideal. Basically, on the 95th percentile days you want your heat pump running almost all day long, just keeping up with losses. Then on the coldest days, you turn on an auxiliary heat source to get you through (heat strips, a fire place, whatever). The systems can (and do) freeze up frequently, but this is why they have a defrost cycle. The defrost cycle for the outdoor part just runs the refrigerant cycle in reverse (A/C mode), stealing a little heat away from your house. Usually the fan shuts off during this part so you don't get blasted with cold air, but it depends on the system. What you DON'T want is your indoor coil freezing up because most systems don't have defrost sensors or defrost cycles for the indoor coils. However, frozen coils are almost always caused by three things: a grossly over sized A/C unit, an undersized air handler and/or ducting, or a very dirty filter. You can also freeze them up by setting the indoor temp too low. Time based control is one of the things that new Nest thermostat relies on. It has sensors to monitor activity in the home (people passing by, etc.) and smarts to measure the lag of the HVAC system and time of day changes from solar input. Then it adjusts the heating/cooling cycle to make sure the house is comfortable when you are there and livable but probably not comfortable when you are not. It is for this reason specifically that I oppose government incentives on wind and solar at this point rather than spending it on basic research. The efficiency is just not there yet, but may be if we put more time into research and making some breakthroughs. [/QUOTE]
Insert quotes…
Verification
Post reply
Home
Forums
Off Topic
The Basement
Home building/living suggestions wanted.
Top
Bottom
Sign-up
or
log in
to join the discussion today!